Table 10.5 Standard reduction potentials of some important biological halt-react
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Table 10.5 Standard reduction potentials of some important biological halt-reactions Reduction half-reaction Acetyl CoA + CO2 + He) + 2e9 Pyruvate + CoA 2 He + 2ee--H2 (at pH 7.0) E (V) 0.48 0.43 -0.42 0.38 Lipoyl dehydrogenase (FAD) + 2n® + 2e'9 Lipoyl dehydrogenase (FADH2) -0.34 -0.32 -0.32 0.29 0.28 -0.23 -0.22 -0.22 -0.20 -0.18 Ferredoxin (spinach). Fe -F a-Ketoglutarate + CO2 + 2 H + 2e-Isocitrate NADp@ + H + 2ee. NADPH Lipoic acid+ 2 H+2e Dihydrolipoic acid Thioredoxin (oxidized) + 2H. + 2e Thioredoxin (reduced) Glutathione (oxidized) + 2 H + 2ee_2 Glutathione (reduced) FAD + 2 He+ 2e FADH2 Acetaldehyde + 2 He + 2ee.-ethanol Pyruvate + 2n® + 2e® Lactate Oxaloacetate +2 H®+2e- Malate Cytochrome bs (microsomal). FC + e-Fe Fumarate + 2n® + 2e9 Succinate ubiquinone (Q) + 2 HB + 2ee--QH2 Cytochrome b (mitochondria), Fe+F Cytochrome c1, Fe, + ee-r" Cytochrome c, Fe+ e Fe Cytochrome a, Fe+ e Fe Cytochrome f, Fe ee--Fe Plastocyanin, Cu2+ + e Cu 0.02 0.03 0.04 0.08 0.22 0.23 0.29 0.36 0.37 0.42 0.43 0.77 0.82 1.1 Photosystem I (P700) 202 + 2 H+ 2e- H20 Photosystem II (P680)Explanation / Answer
1. The half cell reactions are,
NAD+ + H+ + 2e- ---> NADH Eo = -0.32 V
FMN + 2H+ + 2e- ---> FMNH2 Eo = -0.22 V
So,
Eo = -0.22 - (-0.32)
= 0..10 V
FRee energy change dGo is,
dGo = -nFEo
with,
F = Faraday constant
n = number of electrons
So,
Free energy change,
dGo = -2 x 96500 x 0.10/1000
= -19.30 kJ
The energy is not enough to make a molecule of ATP from ADP and Pi.
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