Principles of Biochemistry
`
`ALBERT L. LEHNINGER
`
`THE }C)Hf\‘S H()PKII\.'S UI\’I‘v'ERSI'l"Y
`
`SCI-IDOL OF I\-VIEDICINE
`
`WORTH PUBLISHERS. INC.
`
`Amgen Exhibit 2006
`Apotex Inc. et 211. V. Amgen Inc. et 211., IPR2016-01542
`Page 1
`
`

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`Page 2
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`

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`This material may be protected W COP‘/l'lEl“ law (Tme 17 U5‘ Codel
`
`4137
`
`CHAPTER 1 7
`
`Electron Transport, Oxidative
`Phosphorylation, and Regulation
`of ATP Production
`
`Now we come to the culminating events in cell, respiration.
`electron transport and oxidativn phosphoryiation. All the enzy-
`matic steps in the oxidative degradation of carbohydrates, fats.
`and amino acids in aerobic cells converge into this final stage
`of cell respiration. in which electrons ilow from organic sub-
`strates to oxygen, yielding eiiergy for the generation of ATP
`from ADP and phosphate.
`An approximate calculation will show the quantitative im-
`portance of oxidative phosphorylation in the human body. A
`normal 7U—kg adult male in a business or:cupation requires
`about 2800 kcal of energy per day. This amount of energy can
`be yielded by the hydrolysis under standard conditions of
`about 2800/27.3 = 384 mol or 190 kilograrns of ATP. However.
`the total amount of ATP actually present in his body is only
`about 50 grams. In order to furnish chemictal energy for body
`needs, the 50 g of ATP must be broken down into ADP and
`phosphate and resyrittiesized again thousands of times in the
`course of a day. l\1lDl‘£3OV(3!‘. the rate of ATP turnover in the body
`must also vary greatly. from its rnininial rate during sleep to its
`maximal
`rate during extreme muscular activity. Oxidative
`phosphorylation is not only a vital, continuous process. but its
`rate must be rogulaterl over a very wide range.
`
`Electron I~'io~;-v from Etiuiistrates to Cl'X_Vf_§f}l1
`is the Sriunre of :‘[t"'P l'Iii.izrgy
`
`Figure 17-1 shows the overall organization of electron trans-
`port and oxidative phosphorylation. In each turn around the
`citric acid cycle. four pairs of hyclrog-(an atoms are removed.
`from isocitrate, mketriglutarate. succinate. and malate, by the
`action of specific dehydrogonases. These hydrogen atoms at
`some point donate their electrons to the electron-transport
`chain and become H‘
`ions. which escape into the aqueous
`medium. The electrons are transported along a chain of
`elect1‘oii—(:arrying molecules until they reach i'i‘_t’i_t_3I_t:‘Vl_1_t‘t’_J_i_T1_ti_‘_t_1_CtV;g_.
`
`Page 3
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`

`
`468 PART 1i Biraezmrgtzticrs andf\.e1e1,abrJIis111
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`Figgizm 17-?
`Tfm flzztr sf1e',~c:! r)_f1'esp1'rutr'on. 5j'1um'11;4 Hm
`0r~r';__g,r'rr uf Hm pairs :),1'f1y(fr:;~,-",1:-:11 mrmh Ft?-
`l’1’1Dt«'f.?[i fry (’ft§>h‘.‘dmgmm$t?5‘. with l1':ms_f':.c:' of
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`Hwir Q mi:tmn_~: [20 "] to NM‘ 1*:It}e7fI‘m1-mn1$;)t'11‘I
`ti:J'1m'n. which carrJ'es them to r,";.\'}.,‘,g',c::a_ .Hr.~d1n::—
`Man of each umm of oxygen reqL1i1‘e5 26'
`“r
`ZH I-}nerg_\" see! frrae d u ri Hg trtlnspmt of r‘;
`prgtir of electrons _fr(m1 _\3.-"~.|JH In cf1xA\'gz‘:21 is
`hLIrne:a'seu‘ 10 cause the Lrcjtzpfted rzynthesis of
`ifmsu Inm‘e.=r:u1z.=s nf ATP fmm ADP and phw.-€-
`phutu In the f,1rr)[1E_£S5 0_f'rJx1"dv:1tI'\'e phos-
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`shown here in nbb1‘m>iuted f0r.n1.
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`lfbiquimme
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`Fytotzhronle C.
`13.
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`1:‘.
`Cylmihrome
`nxidase
`
`ADP
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`+ p‘,
`
`ATP
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`ADP
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`Page 4
`
`

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`lrtist
`rrarlieai“ fmm the
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`patliweiy leading to the terminal t-Eleflfrfltl &1fI(I{:1]‘.]l0I‘. mx).~'gt3I1.
`The m«;pii‘at0r_\r (,il1,8.it1 ucntsists of a (~$t}I‘it).‘u' of pmtnins with
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`to CII2\’},'gt:3T1.
`the czmtiplecl sytttlmsis of
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`The tliree segments of the mspir;—,itor_\«" txhaiii that pmvidu €,3t1(£I‘gj,:'
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`Electron Transport and Uxidatiw: Pll0S]}l‘ttJI!'}v'lE1llDI1 Take
`Place in the lunar Mitocxllnndrial Membrane
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`l‘f:':—
`In e1_1l<arjt»'0tic cells Iiearly all the spt:t:ih£: tl€l't:¢'(l]‘CJgE¢I],flSEtS
`quired in the U>=:idati01'i tin“ pyimivatti and (]1,l1t3T fuels via the citric
`acid cycle are lzjcatecl in the inttzmal c,:m1ip;irt1iis3nt ()fl”l"tltOCl1OI]-
`dria. the r_11_a_trix_ [Figtire '17-2].
`'1'h<,;~. mim:tmn~treinst'erri.ng mole-
`czulezs of the rt;a.s‘pir;—itcJry chain and the ti:nzyIi’1t.e 11mlcar,:ule,2s that
`S\’Iltl’1E)SilZE7} ATP fmm ADP and ptmstizhattiz em: c':1nbnclrlr:tl in the
`inmzr immihrziim. F114,-its; at the tiitritz aciirzl. cjstzle. such as pyrii-
`vate, must pass from the t:jutrJs0l. whem lllt-3_t-’ are forlimrl.
`through both mit0c:lmm'lrial nminliranes into the intrzrtial ma-
`trix compartment. wltama
`tlm_\_r are atztetl upcm by (lt3‘l1}’—
`tlrogeiiases. Similarly.
`the ADP torment
`train ATIV’ during
`ens3rg_V~reqL1i1"i11g acztivititrs in the (:_Vt(J$-'.Dl niust pass into the mi-
`ttachrmdrial matrix. to be ]”8[Jl1t']St}l1t'Jl‘jtFlitt(3t'l
`tu ATP. The new
`ATP formed must then pass back to thee uytasol. Special mem-
`brane t1‘a11spm"t systenis [_pagt: 4515‘)
`in the inner mitochonclrial
`membrane promote not only flu: tmtry of pyrtivatiae and other
`fuels inln the 1']ttll',)('2l‘iOl1[ll'lEt but alsu the cmtry 0l:pl1D5|Jl,'l‘d1E} and
`ADP and tl‘It,? exit of ATP (luring oxirlativn pt1c1sphnry|ati0ti..
`
`Page 5
`
`

`
`47!)
`
`I‘.-\R'I‘
`
`J: Bineiiergtztics and Metabcmern
`
`l"igti1':2 1.7-.2
`The l1im;iit:mir't,:nl nrrutr.:m_t' r1_frnitor:l1(:n-
`t'iI'icI, 5imn'ing the iumrinn r;:_t' the t.’,‘I1Z_t,-'tI1E?.‘,-3 at
`the r.'itrIc' mziti !..‘_‘."tJll,‘. the electrnn—tn‘:ns4pm"t
`(:llr1itt:;. the iaiizt'rtit;*s r,:titui_t'7.ing oxidutive
`phnspltoryintinn. and the inI‘n:rnr.1l pool of
`CtJ&‘l1Z_\-‘E1185. Tim inner mr;2ml)rune of ti single
`liver l'I1iif.J{.‘l‘t{}I1riJ'i(JH Imiy have met '1tf1.llfJU
`sets tit ulu(:irmz—|'mn5pnrt rshctins and !\,TP
`$_t-'rrti1etrimr iltrnitttztrima. The m_1n1ber'r.rt'.~';eIs is
`prnpmtionni tn the area at the inner mem-
`bmnrz. Heart rnitcrchrmriria. which have very’
`nro_t'use cjrietne nnri thus U much it‘r1”,_£',BT nren
`raj’ inner ntemhrnrie. C'DJ'1i{lili amr 3 times {is
`mrm_t' stats of e'1im‘:tmn-tmImport Systcertts as
`live-Jr“ mitr,mhmn'iriu:L The intermit peel off
`E08212}-‘[7185 and internmr,iinIr,=s is tLim:ti0ncill_v
`separate frmn the r‘:ytn:;nJ'iz: peel. See
`Chapter 2 fur r.9tl'i4.~r rietnils of Fl'1iif)Cll{J'I1[lI'i[Il
`.‘:'iflJ{.‘i[[l'€~,3.
`
`inner’ rnernbrmier
`It contains the elet;tr0n—trEinSp:‘Jrt
`chains. simtginate (l(a"l'l_\’Ei]‘(,)g[3I'tflSt‘..
`ATP-synthesizirtg en7._\r:ne5. anti
`several mern,l.:ran,e tremspnrt
`sysients. It is impei7Ineal)le.=. tn
`Innst small inns.
`
`Matrix;
`
`The matrix t,:utnpe1:'tn1er1t tzgmtains
`most at the citric m,:ir_i cf,-‘rxle
`en7.j.'mes, the pyruvate
`dehytlmgenase system. the Fatty
`acid nxiclatien systeni. and many
`()il'1.F,:J‘ t2I‘1Z_\~'m(‘.S. It also tznntains '
`ATP. AITIIP, AMP. [Jiu_a5pl1:itn,
`NAD. NAIJPt and c:(>t:n7.ytne A,
`Also present are K’. Mtg”.
`and Caz".
`
`[Tristae
`
`W
`
`(Jitter ineiiihmm;-:
`it
`is fnzt‘,-!.\-' ptzrmeable
`tn nmst small nmlerzulns
`and inns and mntains
`smite rmzymes.
`
`inlrzuizristril
`space
`
`Inner
`membrane
`
`ADP
`‘l’ P.’
`
`ATP
`
`Matrix space
`
`lnturanenibmne suture:
`it ttnntains aczlenylate
`kinase and nther ezizymes.
`
`ATP s_t'r1tlmtas;r~ molecules:
`Their base pieces are located within
`the inner meinbrane. ATP is made
`in the matrix as Sl1CtWI1.
`
`The inner mitochondrial membrane is thus a cninplex struC—
`ture. containing the electron-carrier rnnleculee, a number of 611‘
`zymes. and several membrane transport systems. which 811-
`together make up 75 percent or more of the total l]‘lC3I1ilJI'El1'19
`Weight, the remaincler being lipid. The inner membrane has -‘fin
`intricate. rnnsait: structure whose i,nteg1‘ity is essential for 115
`life-stipporlitig activity‘ in generating ATP‘
`
`Piletitm:1u"I't'2}11si't'n‘t‘i11;; Reatztinns ,=‘ta‘u:
`ffixiilattimviietiiltztiett t?.e;aCtinI3+~:
`
`Although we have extilninecl some enzy1ne—catal_Vzetl l‘t}at‘.[i[‘JI15
`in which ltyclrogen atoms or electrons are tramferretl frmn en:
`1n0it:r,:L1le In another, we must new review the properties 0
`
`Page 6
`
`

`
`(:nM='r|n1 '1?
`
`l7.lect.run Transport. Oxitlative l’hrJ:+pl1orylaIlor:. mul Regulation of .r*’5.'|‘P l’md,uction 471
`
`such reactions in :1 more quantitative way: Chernicnl reactions
`in which electrons are transferred from one molecule to an
`other are called oxirlcxtion-reclirctfon reorttions [also oxidore~
`cluctions or redoét
`T i1-lHo1ir:rii11.g niolecnle
`in stilchlla rezictionlilsmcfalletl-the rerl u i'orEnli1(:i:i:r1t; the
`elm.‘tron—n:1t:c:c;Jllng molecule is
`(J.>{lt_llzlIlg,ML1g(;‘ltF-U1‘ (JXl(,lf11il.
`it WR”e_d’filcing anti
`n3EHi}fi11'g
`ager1t.5;mt'u1ictiEf?s.
`c:§fi'u’g?f:%:
`reductnni~oxirloni pairs [redox pairs]. just as article and bases
`fnln Ellllar:iEfBase: pairs [page 78). Recall that in
`acid-base reactions we can write the general equation
`
`Proton donor 7:: H "
`
`proton acceptor
`
`in redox reactions we can write a similar general equation
`
`Electron donor :r— e“ + electron. mjtceptol‘
`
`A specific example is the reaction
`
`Fe“ is: e’ + Fe”
`
`in which the ferrous 1011 We“) is the electron donor and the
`ferric ion {Fe“"] the electron acceptor. Together l'*'e“"" and Fe“
`constitute a conjugate redox pair.
`Electrons are transferred f_rTfn one molecule to another in
`one of four different ways:
`
`1. They may be transferred directly as electrons. For example,
`the Fe“”‘—i*‘e"“
`rcclox pair can transfer an electron to the
`Cu*—CL1'""‘ redox pair:
`
`Fe”‘‘ + Cu“ —> Fe“ + Co’
`
`2. Electrons may he lransferred in the form of hydrogen atoms.
`Recall that a hydrogen atom consists of a proton (H"] and a
`single electron (e‘].
`in this case we can write the general
`equation
`
`Alrlg +4 A + 21:?" + 2H‘
`
`where AH; is the hydrogen {or electron] donor, A is the hy-
`drogen acceptor, and Al'lg and A together constitute a con-
`jugate reclox peir, which can reduce the electron acceptor B
`by transfer of H atoms:
`
`AH? + B ?'> A “t EH2
`
`3. Electrons may be transferred from an electron donor to an
`acceptor in the form of a hydride ion [=ll‘]. which bears two
`electrons, as in the case ol5‘l*:lWAD—linl'{ed dehyclrogenases [see
`page 236].
`
`Page 7
`
`

`
`472 P.-H21‘
`
`[I
`
`l'ti4‘;ene:';,:,etics and M4’.-tal';olis:rn
`
`4. Electron transtier also takes place when there is a cl.irect cum
`hination of an organic reductant with oxygen. to give a pl-Ud_
`not in which the oxygen is covalently incorporated. as in the
`oxidation of a hyclrocarlimn to an alcohol:
`
`R—c1~c + got —> i<—t::i-c—-oii
`
`In this reaction the lijxdrocarlion is the electron donor and
`the oxyg(:,i1 atom is the electron acceptor.
`
`All four types of electron transfer occur in cells. The neutral
`torni reducing ecjuimlerit
`is coinrnonly used to designate a
`si11gle' tEJeWt participating in an oxidoreduction,
`whether it is in the form of an electron per se, a liydrogen atom,
`a hydride ion, or takes place in a reaction with oxygen. to yield
`an oxygenated product. As we shall see. in mitochondrial elec-
`tron transport electrons are transferred in different forms, as
`hydride ions, as hydrogen atoms. and. in the later steps cata-
`lyzed ti); (,:ylOCl1I‘CII"flBS, as electrons.
`Because biological fuel molecules usually undergo enzy~
`matic dohjgclrogenation to lose two reducing equivalents at a
`time. and because each oxygen atom can accept two reducing
`equix-'ale1'1ts, it is customary to think of the un.it of biological ox-
`idalions as a pair of reducing equivalents passing from sub-
`strate to oxygen.
`
`Eacli Conjugate Retlox. Couple Has a
`(Iharacteristic Standard Potential
`
`The tenclency of a conjugate acid-base pair to lose a proton
`reversibly is given by the dissociation constant K {Page ml‘
`Similarly. the tendency of a given conjugate redo): pair to 1059
`an electron can also be specified, quantitatively hjc a constant.
`the standard oxiclotion-reduction potential E’). This is defined
`as th TllH7t?iHT?§i\7?n by a responslvfl
`electrode placed in a solution containing both the electron
`donor and its conjugate electron a(;ceptor at 1.0 M concentT3*
`tion. 2:3"’CI_. and pH = ?.U [Figure 17-3]. The electrode must lie
`able to accept electrons from the electron donor and Clflllale
`theni to the conjugate electron acceptor. Such an electrode H11‘
`niersed in a mixture of the conjugate redox pair coustitut85 3
`troll
`:ell. In order to determine its emf it must he electricalll’
`Efiiiiectecl to a rejterenco liolficell whose emf is known llllgule
`t,7—3j. The t1ltirWcfi(%_r_ell?ErE‘I11ce_"h_Eilf-cell
`is the l1_\t't't1‘0.i%9" elm-
`ll‘U(,lE.‘. which has an emf arlaitrarily-’ set at zero \«‘l*Tt‘E‘-_tlMl—-"
`V
`ls
`in equilibrium with '1.Uatrn Hg gas at 25"(I at pH 0. At DH 7- holl-
`ever. the l1_VClr0E—’.en electrode has an emf of i-0.41 V lfigure
`'l 7-3 .
`Itlis the convention in biochemistry,-' to express the stflllllafil
`potentials of conjugate reclox pairs as rectutrtion Ittffiienjillwl-1
`whicli assign imzreasirigly negative values t"E_i_"s:i7s‘t5ii1sl13"‘”ig_
`an increasing |er’irleiic)..' to lose electrons. and inr_:reasi11?»l3’P0S
`
`Page 8
`
`

`
`
`
`ffjg[i;'r- J7-It
`
`:1_f'I‘lw .~‘lt.‘I](lt1i'tl rer,ilIir:tJ'nr1 pu-
`.\ler.L»“z1raamrenl
`f,_.;;ej:2l.
`'lln_".';olz1tioi1 Ii'{}Illttll?li1_§;‘ the mr'_\'rI,Jre
`of 1.1.1 Xi u.\;iu,lim-ll uml rmlm;'cr.l tr,m'r'I.a' of tin‘
`”’,{fU;t-
`:_;.=:iuplr: to l,}(?‘ nxmniriml is plormi in
`llitf!‘t_11li1 1.'e,s.=;sel.
`'i‘l1e elecIroz‘J'e.
`ll§w‘LJIilll_1’ plut-
`inum.
`is ;.‘tJ.'2lli,3tL"l1,‘tl by on l;"XI€.'rmi1l
`4,:ir‘c:uit
`to
`G p,2_r‘en:.-i1r;i> ln:l_t'-col l of ca
`t't.?(|'().\' esouple of
`knotm potential [at the left}. Wu‘ ultirmzte
`ref(.‘t‘I;?tii'P cell or the li_1"o‘roger: 4.-ler:irot,ie, o
`pl-utlliltfil electrode in r;onr,oct witlt LU .,\/ll I-ll
`[j_¢1._, pH [1] mm‘ .s:rtur.rztet;l with ii._.gos at 1.1]
`atm. ‘.'.‘l?l('7lt is nrhitr'nriiy rissigzwerl n :a‘tom:lorri
`pm:;nriol at (H1. Tim eler.'trorlr:5 con e;icci':;zt
`gr rlonnte eler:Irr_;nns to the reolorc couple in
`each II‘-‘ill, o',epr:izr,lin_g izpon their i'e.~;per_:tiwr
`potentir,:l.<. A Stlll l'zri:i_;;e cmttoining o .wotL1-
`mterl Kill mlution prm=io'e.~; on e?lectrir.:ul con-
`nection l‘mm*een the text cell mm‘ the i‘t‘:/t'er-
`ence mil.
`i;'le:i.'tr'om* will _J'To1\' from the 1:23!
`electa‘oalr_- to the I'P_l"(3t‘f‘,‘J'Ir;Z‘E r;ler:tro4.le. or irir:r,.-
`verse.
`'.:"n the E‘.\Zi[.‘fltt'Jl c:irr::uit, in u <1‘iz'et.:tioi:
`depending upon the rrrloliwa electron "pmrav
`sure" or gworentiol otthr: two cells, but
`alwrns ft’-:'::11 the cell of more I1!1‘gf.1llt'(.* to the
`cell c)_tmuI'{.‘ }]1(l.Ex‘lil'n’(.‘ potential. Front the
`ohsertml einf and the known emf of the
`refertjrltflf m:-ll. the r;n1_‘t"r2_f'tl1:e test well mn-
`tuining llm t'(.H.lDX couple is ol3ior'nerl_
`
`r.:IMP'J‘t:i< ti‘
`
`I,-Ilu:ac;tron 'l‘r.'i::spt'n‘t. {)7-;icl/miw I‘|‘m.e;nl1or_\*l;ition. Eittll islegulation oi ATP l3mrl‘.1t,:f,ion 473
`
`Uti\"l{:t! fin‘
`:'iIe;as11ring; zanit
`
`H,
`
`1'11] itlilt} Kt}! .-solL1tion
`
`
`t<e':ierenc:e ltoli-cs.-ll of
`l~:nown emt. The
`ultim.--ite .<,+t:—m(la1‘t'l is
`the l‘i_1.'r;l1‘:1,ge11 electrode
`HlJLJ“.‘(). in which H3
`gar: at H! atm is
`eqiiilihrntetl at the
`electrmle with l M
`ll". to give an
`Eli‘lIit1“€!!'}.' emf of
`U1] V. The hf.
`of tlw l1_\"{lI'(')‘b'E,’l"1
`tZl()[Il1‘t)f'l(:‘ at [all 7.[l
`is
`U,-ti V.
`
`"i"eet h:ili—r;ell
`coiutatinirig i.'vi
`z,:onc:entrz:ti,on_~; of
`the [J\'t(ll7.Bf.l and
`retlucecl .«;_necies
`of the rotlox
`couple to he
`f.'.I‘(Eii'i1li"IU(l.
`
`tive values to systems having an incgreasing terirleilcy to accept
`electrons. The terms .s'tandord reduction potential, standard
`potential, and stonrjiorrl rntidrit'ion:reduction pcftentiol aieusetl
`iTt_e1“f.'hEi11geabl3t'.
`'
`V
`V
`l
`V
`l
`7'”
`V
`Table 17-‘! gives the standard reduction potentials of a
`number of conjugate redox pairs important in biological elec-
`tron transport. They are listetl in order of increasing potential.
`in the order of ciergreasing tendency to lose electrons. Thus
`conjugate rodox pairs havi11g relatively negative standard po-
`tentials tend to lose electrons to those lower in the table. which
`have more positive standard potentials. For example, when the
`iSUf:liI‘E1l(3/'05-l(8'[OglUtafiile + CO2 couple is present in 1.0 M cron-
`oentrations it has a standard potential P3,} of -=~ (1.38 V. This reclox
`couple tends to pass electrons to the redox couple NAI3I~I/NADT.
`which has a relatively more positive potential, in the presence of
`isocitrate (lehydrogenaso {page 445]. Conversely, the strongly
`positive stanclard potential of the water-oxygen couple. 0.82 V.
`indicates that the water molecule has very little tendency to lose
`eleclrom; to form molecular oxygen. Put another way, molecu-
`lar oxygen has a very higlt affinity for electrons or hydrogen
`atoms. Although standard potentilals are given in units ofvolts.
`they are often expressed in rnillivolts for coiweniettce. ——_
`
`Page 9
`
`

`
`474 PART ll Birgeiitrrgeticn and Metabolfsni
`
`Tolile 17-1 The Standarrt Retitictirm Potentials Hf. of Seine tflorijugatz: Redgx
`ijouples PHrtic:ipatin,r; in (,):><id-ativrz Metabolisnrt
`
`Reriox couple
`
`Suiiie .«;L1lssti';stt'* t;uL1pli.*.~J
`-4- 2e’ --~> pyrtivate + COA
`Arjety-‘l-(_‘.m\
`+- CD3 + 2H‘
`o~Ketogl,iit+iretr: + {JCJ2 + 2H" + fie ——> isocitrate
`3-}’l1o5pl1oglyr:oro}.-'l phosphate + 2!!‘ + 2:} —>
`gl};ceral(leliycle ;;t—phospl'ia,te -r P;
`Pymvate 4- 2H -4- 2e — -> lactate
`Uxailoacetate + 2H‘
`2e’ v—-9 rnalnte
`Fmnrirate + 2H‘
`! Zen‘ ~—w> si1:::r;:inatt':
`
`l::t!lt]]}t3l't€fi1lS til‘ ll1t,' ultr(,tmH-tré:mi;m1't izliziin
`EH" + 21*’ —-—-'- H_.
`l\'AD‘” + H‘
`F Zr?
`l\."A[Jl4’"" + H‘
`*1‘ 2::
`
`-—+ NADH
`-
`-4- NAUPH
`
`NAUH dehytirtggtenase {F-‘MN forrn] 4- 2li“‘ + 26'‘ :>
`NADPI rlrzhydrogenese [F.\'1l\'t‘l,;. fo1‘mt
`
`5;,
`
`-5143
`-0.33
`
`-1129
`—g.1g
`—u_1g
`+£1.03
`
`*[l.4’t
`-0.32
`"1132
`
`-0.30
`
`‘
`l
`
`.
`
`’
`
`i
`3
`
`l
`
`;
`'
`
`+0.04
`+0.9?
`
`+0.23
`
`+0.25
`+0.29
`+0.55
`4-0-82
`
`Uliiquinmic 7 2H’ + 2e’ —v ubiquinol
`Cytoclironie b (ox) + e —> cytochrome b {red}
`
`Cytochrome C1 [ox] 4-
`
`1,!
`
`-~—-> cytociirorrie tr,
`
`[ymrlt
`
`——-==-+ cjutoohronie r; [red]
`ra
`tI_\'tor:lirome C fox] 4-
`Cytochrome (1 [ext t (2 —-v> C}/tochroiiie (.1 (red)
`Cytochrome (13 tux) + e” —Jr cytochrtirmz -13 [Ted]
`in. + in 1» 20" ——~ mu
`
`+ Assuming ‘1 M concentmtions of all mrnponents, pH = 7.0, and 25”C. Half-
`rezictiomi which express the affiriit}; of each system for electrons are shown.
`The more me alive the E4. the lower the affinity of the systein for electrons.
`Conver5elj.,z tie more positive the E’, of a eystreni. the greater its electron af-
`finitjg. Thus electrons tend to tlnw from one redo): couple to another in tha
`direction of the more positive system. Two landmark potentials [color] are for
`the H-¢f2H" couple and the I-i2(_l;’%t}2 couple.
`
`ltlI‘iv!I€*EIiE3i‘}:§f.‘
`
`tilieiiiges Pttrrtztiiiigiziriy Eiectron 't'reiris-;i’-me;
`
`The E5 values of various redox couples allow us to predict the
`direction of flow of electrons from one redox couple to another
`when both are press-n.t under standard conclitions and a catalysl
`is available. Electrons usually will not flow from one redflx
`couple to aiiotliei‘ unless 8 catalyst or enzyme is present to
`accelerate the process; the catalyst, however, does not aiter the
`direction of flow or affect the fine] equilibrium attained. Llnclef
`such conclitions. elecztmns will tend to flow from a relatively
`clectronegative conjugate rodox pair, such as NADFIINAW
`[M3 = — (1.32 V],
`to more eletitmptisitive electron zit:ccpt0T5*
`such as 1‘educed (:3-‘tt)clirmi1e cftixidized cytochrome if
`llstl :
`+0.23 V}. Similarly.
`tlie}; will also tend to flow from the C?"
`tochrome C reclox pair to the watermxygen pair [E3 -= ‘t (3-32 Vl’
`The tenrlency for electrons to How from electronegatiw: toward
`eloctropositive systeiiis is the result of the loss of free €I1f3T33l‘
`sl[‘1[;t'3 electrons always tend to move in such a direction that the
`free energy of tho reacting system decreases. The great” lhe
`t‘tiffe1‘e1ice in the standard pottjantials between two rerlox Palrs’
`
`Page 10
`
`

`
`CIiM"I‘ER '17
`
`ltllectron Transport. Oxirlative Pbosphor}-'latiuIi. and Regulntimi of All’ l’rorluc.;l,ion -175
`
`the greater the free-energy loss as electrons pass from the elec-
`tronegative to the electropositive couple. Therefore. when elec-
`trons flow down the complete electron-transport chain from
`NAD1-I [E5 = —~ 0.32 V] to oxygen [E3 : +0.82 V], via the sev-
`eral
`electron—carrying molecules of
`the electron—transport
`chain. they lose a large atnount of free energy because the dif-
`ference between the standard potentials of the redox pairs
`NADH/NAD‘ and H20/$02 is relatixlely great.
`Let us now calculate exactly how much free energy will be-
`come available as a pair of electrons passes from NADIJ to ox-
`ygen. The standard-free-energy change of a reaction in which
`there is a transfer of electrons is given by
`
`AG” : —n.§5 _'\E,'.
`
`where AG“ is the stancla1‘d—free~energy change in calories, 11 is
`the number of electrons transferred, 9}‘ is a constant called the
`fcirggox [23,Ut32 cal/V-moi], and A55 is the clifference between
`the standard potential of the electron-donor system and that of
`the electron-acceptor system. All components are assumed to
`be at 1.0 M concentration at 25°C and pH 7.0. The standard-
`freeenergy change as a pair of electron equivalents passes from
`the NAIJH/NAB" pair {E4} = -0.32 V]
`to the H20/{<02 pair
`[E5 = +0.82 V} is thus
`
`AG“ = —2(23.oe2][o.s2 — [—o.32)] = -52.5 kcal
`
`The 52.6 kcal of free energy released as a pair ofeleotrons passes
`from NADH to oxygeli under standard conditions is clearly
`more than enough to bring about the synthesis of three mole-
`CLllBS of ATP, which requires input of .3[7.3) = 21.5} kcal under
`standard conditions.
`
`in the same way. using the expression AG“ = — ob?’ M253}. we
`can calculate the free-energy changes for individual segments
`of the electron—trar1sport chain from the clifferences in the
`standard potentials of the electromrlonating redox pair and the
`electron-accepting pair. Figure 17-4 is an energy diagram
`
`— (1.4 a
`
`— 0.2-
`‘
`
`t[:.t,"!l
`
`f\'AtJH—>I£
`ZEN
`
`i
`I-‘.‘»<tt\'
`
`2e"
`
`=.
`“IJ
`
`-
`
`I')ire(;tim'1 at electron flow :4;
`
`Page 11
`
`Figure 2?»:
`The direction of How of electrons mm‘ the
`energy‘ relorlonsliips in the respimtory rrlmln
`‘Pf mltoclmriazlrirr. E—FMN l‘t',‘f'Jl'E.‘.h‘8I1lS NAIJII
`dBh_VC1‘1”og::-rnise. Q is tJlJlqtlll1(}t1!-I, end 1). Cl.
`C. anrl a rejJt'ese11t C1-'lI,1f,Jl1I‘IJITl€S. Note that
`there are three steps [colored arrows) in the
`ele:;Iron~tmnsport chain in which relatively
`large (lt?Ct”[?{l)4St2'h' in _tre.i':
`t’.‘t1t,3I‘g}‘" occur as eter-
`”°”9 l’J€IHs. Tl1esr:- ore the steps that pruritlte
`lrfle enr3r';4_\' for A’l"1’ A‘.’l~‘{t]t]1E3I.(l:I-l.|;A
`Tobie
`17‘1lUr the lit". vrtlues for tlie electron cm-ri-
`ers.
`
`

`
`Sl'1(‘J'WlI']g [ii the stantlarci potentials of some of the electron car.
`riers oi’ the respiratory chain. [2] the direetioii of electron flow,
`which is always "rimvnhill“ toward oxygeii. and [3] the rela-
`tive l'ree—energy cliaiige at each step. Note that there are large
`free-eriergy clecrezisras in three of the steps along the electron.
`transport chain. These are the energy—tzonserviiig sites that pm.
`vitle t:i1r:i‘gy for ATP synthesis.
`
`There Are Many Electron Carriers in the
`Electron-Traiisport Chain
`
`The respiratory chain of mitochondria contains a large number
`of eler:ti‘on-rterrgring proteins that act in sequence to transfer
`electmns from substrates to nxygeii. Although Figure 17-1
`shows the respiratory chain to have seven electron ca rriersi this
`is an ‘ril)bI‘E3‘\»"l,E]i(3Cl representation. There are 15 or more chemical
`groups in the electron-traiispert chain that caii accept and
`transfer reducing equivalents in sequence, suiiiinarized in Fig-
`ure '17-5.
`
`Note the several, diiTere1it idncis of elet_:tmn—carrying groups.
`associate:/l with proteins. They inclucle i_i_ic:'itiIioiriide
`all
`mienine riirrimleotirit: {NAB}. active with various clehycirogen-
`jlcrvin mcmonucleotirle [i’;\I'lN'}. in NADH ciehytiregeriase:
`tibiqriiimne er ceenz_ime Q, an isoprenoid lipici—solL1ble qui—
`none. which functions in association with one or more proteins;
`two different kinds of iron-containing proteins, the imn~sulfur
`
`centers {Fe—S] and the trjvtochromes: and copper of CElln?“tFGme
`third lI11,}Jt)I‘tE11]$E1T?tl1.Eii nearly all tiFelectron~
`lca1*rj,.-'ing proteins of the chain are water—insoluble and are em-
`l)t;3ClClE‘,[l in the inner initochontirial membrane.
`
`The Pyridiiie l'\3uoleotides Have a Collecting Function
`
`Most of the electron pairs entering the respiratory chain arisfl
`from the action of tleliyclmgeneses that use the cnerizytilefi
`i\2AiJ‘ or l\'Ai.)P‘ [Figure t7—t3) as electron acceptors. As 61 gr01IP
`they are (iesignateci
`the i\:’AD[P]-linked tieli_v(lrogr:iit,rs:§. W9
`liave already met several sncli Ciel1j.’ti]“l3gE,3I1EtS€.S
`in our discus‘
`sions oi" gi};r:oirysis and the Citric acid cycle. but niaiijy more fife
`kriown. Some important ones are listed in Table '17-2. All cata-
`lyze reversible reactinn.~; of the following general types:
`
`Ret,ir.ir:ecl substrate t NM)"
`
`E]XiLiiZE3t'l substrate + l\'-A]'Jt'i
`
`-+ H’
`
`l{etim;eL'i sul,1.sir‘att-:
`
`V-‘ i\'r\i)P'
`
`oxiclizenl st1hstr:_1te
`
`i\Al1IPil
`
`*’ H
`
`The great 1najorit}.= of the py"riciiiie—iinl<er.l rieliydrcigeiiases £1-T3
`ss}.)er,:it'ir: for NAIJ‘ [,'1“alile '17-2]. liowevei‘. certain otliers reftmle
`NADP' as electron ar:c:ept0r. sucli as glucose t.i—rJli:9siJl}Qf_fjjl£'
`i‘ttr'n[li‘(J§f.§(‘I?{I;H,'t? {page 4:37]. A very few. srcll as glrilflrrhiritc (l0_l_Ll"'
`,§4t‘.*rir{._<e.
`€,IFiI'1 react with either NAB“ or N/\l)P‘ [TflTT)iTt,3_T‘7'2]'
`
`
`
`Page 12
`
`476 PAIt'I'
`
`1:
`
`lil(J£?i1tj]“g(':iiCSHlltli‘»-irziiilitilifiiitt
`
`Q." the
`{li
`lmisi
`
`i’i,g_;Lit‘c'.* £7-33
`'l'l‘rz.~ r;:u13i}Jlt3tr'- Sill at t*lm‘:tr'm'i 1,'riJ‘i'I'ta
`I'espir'¢‘itzir_i‘ rimin. in site 1 there r.Il..
`five zi1'_f:r’ee*eni
`iroii-su,l_ti.ir r,:er-,g,p,-:,g In sit»: 3
`Iltm‘r.+ ere [WU rli,t‘ytere':r1t
`l‘r,:II'i'I'I.‘~, of t,".'lI11tl‘l1I‘£Il?‘r(j‘
`h, with riijtfererit
`li}J,l'IlAfJb5‘t1‘}JlirJ21 fl(.?t]l\’.‘1'. us
`irell as an imri-siil_t‘Lti' center lii.H‘iit't('1l
`te‘r,ziri
`those in site ‘1.
`in sit
`
`i Il'im'{' v.“ir‘r“'
`itmu t':r.J}JpPr
`lens in r:ru‘u'i|iv.m tn tZ_\‘ir.ItIltI"r)H1HH ti fiitii #15.
`Tim ;m':r.i::t> st:-:;iiernr:z: rmrl _i‘Lrn<:tinn at till the
`reriox centers is mat i<nrm=n with rr=rtrn'ntj.‘.
`
`
`
`Sill]:-'ill‘z’2lE3
`
`Site ‘S
`
`I
`
`Site 2
`
`Site is
`
`
`
`tie”
`Uzi“
`
`E’),
`
`

`
`cit.-\i=1‘1:Iz 17 ljlectron 'l‘rar15;:mJ‘t, Oxitlative Pliospliorylation. and Regulation of ATP Prodimtign 477
`
`
` contains
`
`a phosphate
`group in this
`position
`
`[3]
`
`Figure 174:”
`Nicotinomicie nrilmiine clirtttcleotide [ii/\T]‘t]
`and nicotinoinidc rzdeiiinn r_linLn:leoticlo
`phosphate (l\3ADP"). ta] Oxirlized }'orms
`{NAD” and NAlJP‘}. i’\‘icntinomirltz [shaded]
`is a vitamin of the B‘ cotnplex tpcige 255}
`and is the portion of the molecule partici-
`pating in m'er;fron transfer.
`fh} Reduction of
`the nicotmmmr,t'e ring of I\lAlJ' by substrate.
`The two redu.r:in,g equivalents ore troiislerretl
`fmm the szil).sti‘ate [clesigiioiml RCHQUH] to
`NAB’ in the forrn of o liydride ion [Ill ].
`The other l1_'r'Cl1”()gtJl"l removed fmrn the Still-
`stmte lie-,r.'mizes HT
`
`(ill
`I
`‘”
`R
`
`(:—:\‘n
`
`(,1
`
`:3‘:
`Ht.‘
`"‘
`ll
`H(,,).,___ mt H o
`'“:N‘’
`.
`l
`R
`
`"
`
`it
`
`r -—(,—wN!L
`II
`t!
`“
`cn o
`
`4:
`‘
`<—'‘
`1*
`
`H
`
`:{ :”
`
`HIZ
`1]
`Hc,
`
`N’
`5
`R
`
`mo
`
`NADH
`
`{bl
`
`Some pyridine—linl<.ed dehydrogenases are located in the cy-
`tosol. some in the mitochondria. and still others in both. Cyto-
`solic deliydrogenases can react only with cytoeolic pyridine
`nucleotides; siniilarly. initochondrial dehyolrogenases gener-
`ally react only with niitochondrial pyridine nucleotides in the
`matrix. The cytosolic and mitochondrial pools of NAD and
`NADP are separated by the inner I‘l'lllUCl'|,UI1Cl1"lE!l mernbrane,
`which is impermeable to these coenzymes. We shall come heck
`to this point later.
`The most
`important NAD—linkecl dehydrogenases func-
`tioning in carbohydrate catabolism are gilyceraldehyjde pl‘lQS-
`chute. ci_e;h.y_ctreg::L1a_§§ and lrictgttt:
`ii,§i,*3l1t:<ir0s.r?r_19§e of
`the
`glycolytic system, located in the cytosol, and 1g§1rgggtrg_dgy—
`ggggengge, present
`in the mitochondria [Table 17-2). Three
`NAD—linl<ecl dehydrogenases participate in the citric acid cycle
`in the IT1liOCl1On(lFla:l§§_1'_J__(;if_l:§fi3, gr-ke_tcgg_lr_4to<i;gr_t_e, and inolotem-;Le_—
`l_1yi;;l_i1ggeIictses. Other mitocllondrial dehydrogertases of impor-
`tance are ,3__-liydroiiztic
`
`Table 1722 Some important Reactions Catalyzed by NA!T}[P]-Linked
`Dehgwlrogenastzsa
`
`.“~3;‘tI]-linktrtl
`
`Isocitrate + .\JAD'' :;
`
`(X-l(E3lIC3gl11tElI'&1if: + CD2 + NADH + H“
`a—KetoglL1tarele + Co!/\ 4- NAD‘-' 1.1“
`suz;r;inyl—Cr)I\ + £202 + NADH -'— H’
`l‘~.’A[J‘” : oxaloacetztte
`NAIJH + tit
`L-Malate ~.’—
`Pyruvate + ("Jo/X + NAT)“ ef-
`acetyl-CJUA + CD2 +» NADH + H’
`Cl_vceralrlcl1_yt_le 3—phosphate + P,- + MAD 1
`tilktliphosphoglycerate 4- NADH + H*
`l.actat.ri + NAB‘ H: pyru.vate '9 NADII 4- H‘
`':“1ill’—liI1l‘ucl
`
`Isocitrete + NAUP‘ """
`wketoglutarate + CD3 + NADPH <1’ H‘
`Glucose 6—pl1osphate
`NADP’ :
`t‘z—p}iosphogluconete + l\EA1’1Pl‘i + H‘“
`
`VA!) or IX‘.-Kill’
`
`L—Glutamate + Il2(J + NAIF {.7\lAlJP'} T:
`gr-Vketoglutarate + NH; + NADH [,NADPH) + H”
`
`t‘ M = mitochondria and (I = rgytosrial.
`
`Location+
`
`M
`
`M
`M and C
`
`M
`
`(J
`{ll
`
`M and [I
`
`C
`
`M
`
`Page 13
`
`

`
`478 mm‘ H Bi0et1eI'gt':tir:s and Metabt')]i§1n
`
`f*"z'ggt11'c- JFA7
`Thee r.::)IJ‘etttitt;—; ftmrrtirm nil‘. NM} and