Page 353 - Thermodynamics of Biochemical Reactions

Chapter 9 Redox Reactions

9.1 Calculate the standard apparent reduction potentials for 298.15 K at pHs 5, 6, 7, 8, and 9 and ionic strengths 0,0.10, and
0.25 M for the following biochemical half reactions and plot their pH dependencies at 0.25 M ionic strength.
(1) O2 (aq) + 4e-= 2H20
(2) O2 (8) + 4e-= 2H2 0
(3) O2 (aq) + 2e-= 2H2 O2
(4) O2 (8) + 2e-= 2H202
(5) cytochrome cox+ e-= cytochrome cred
(6) pyruvate + 2e-= lactate
(7) acetaldehyde + 2e-= ethanol
(8) FMN,, + 2e-z Fm,,d
(9) retinal + 2e-= retinol
(10) acetone + 2e-= 2-propanol
(1 1) NAD,, + 2e-= NADred
(12) NADP,, + 2e-= NADP,,,
(13) f erredoxin,, + e-= f erredoxin,,d
(14) acetylcoA + 2e-= coA + acetaldehyde
(15) 2e-= H2 (g)
(16) 2e-= H2 (aq)

9.2 Calculate the apparent equilibrium constants K at 298.15 K and pHs 5,6, 7, 8, and 9 for the following four reactions and
plot the base 10 logarithm of K versus pH:
(1) N2 (8) + 8 ferredoxinred= 2 ammonia + H2 (g) + 8 ferredoxin,,
(2) N2 (aq) + 8 ferredoxinred = 2 ammonia + H2 (aq) + 8 ferredoxin,,
(3) 2 ferredoxinred= H2 (8) + 2 ferredoxin,,
(4) 2 ferredoxinred= H2 (aq) + 2 ferredoxin,,
Note the ionic strength is not mentioned because the reference reactions and the dissociation of NH4 do not depend on the
+
ionic strength. Note that the apparent equilibrium constaants of the first two reactions change by a factor of 10 when the pH
is changed 0.10 in the neutral region.

9.3 Calculate the standard apparent reduction potentials of the following half reactions involving carbon dioxide at 298.15 K,
pHs 5, 6, 7, 8, and 9 and ionic strengths of 0, 0.10, and 0.25 M and plot them versus pH at ionic strength 0.25 M.
(1) C02 tot + 2e- = formate + H2 0
(2) C02 (g) + 2e- = formate
(3) COz tot +pyruvate + 2e- = malate + H2 0
(4) COz (g) +pyruvate + 2e- = malate
(5) C02 tot + acetylCoA + 2e- = pyruvate + CoA + H2 0

9.4 Calculate the change in binding of hydrogen ions in the following 10 biochemical half
reactions at 298.15 K, pHs 5, 6, 7, 8, and 9 and ionic strengths of 0, 0.10, and 0.25 M. Plot the change in binding at ionic
strength 0.25 M versus pH.
(1) C02 tot + 2e-= formate + H2 0
(2) C02 tot + acetyl-CoA + 2e-= pyruvate + CoA + H2 0
(3) ketoglutarate + ammonia +2e- = glutamate + H2 0
(4) pyruvate + ammonia +2e- = alanine + H2 0
(5) pyruvate + C02 tot + 2e-= malate + H2 0
(6) cystine + 2e-= 2 cysteine + H2
(7) citrate + CoA + 2e-= malate +acteyl-CoA + H2 0

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