Compare the delta ΔG0' values for the oxidation of succinate by NAD+ and by FAD. Use the data given in Table 18.1 to find the E0' of the NAD+-NADH and fumarate-succinate couples, and assume that E0' for the FAD – FADH2 redox couple is nearly 0.05 V. Why is FAD rather than  NAD+ the electron acceptor in the reaction catalyzed by succinate dehydrogenase?

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Compare the delta ΔG0' values for the oxidation of succinate by NAD+ and by FAD. Use the data given in Table 18.1 to find the E0' of the NAD+-NADH and fumarate-succinate couples, and assume that E0' for the FAD – FADH2 redox couple is nearly 0.05 V. Why is FAD rather than  NAD+ the electron acceptor in the reaction catalyzed by succinate dehydrogenase?

 

TABLE 18.1 Standard reduction potentials of some reactions
Oxidant
Reductant
E, (V)
Succinate + CO,
a-Ketoglutarate
Acetaldehyde
Ferredoxin (reduced)
H,
NADH + H+
2
-0.67
Acetate
2
-0.60
Ferredoxin (oxidized)
1
-0.43
2 H+
2
-0.42
NAD+
2
-0.32
NADP+
ΝADPH + H ,
2
-0.32
Lipoate (oxidized)
Glutathione (oxidized)
Lipoate (reduced)
Glutathione (reduced)
2
-0.29
2
-0.23
FAD
FADH,
2
-0.22
Acetaldehyde
Ethanol
2
-0.20
Pyruvate
Lactate
-0.19
2 H*
H,
2
-0.00!
Fumarate
Succinate
2
+0.03
Cytochrome b (+3)
Dehydroascorbate
Cytochrome b (+2)
1
+0.07
Ascorbate
2
+0.08
Ubiquinone (oxidized)
Cytochrome c (+3)
Fe (+3)
½02 + 2 H*
Ubiquinone (reduced)
Cytochrome c (+2)
Fe (+2)
2
+0.10
1
+0.22
1
+0.77
H,O
2
+0.82
2.
Transcribed Image Text:TABLE 18.1 Standard reduction potentials of some reactions Oxidant Reductant E, (V) Succinate + CO, a-Ketoglutarate Acetaldehyde Ferredoxin (reduced) H, NADH + H+ 2 -0.67 Acetate 2 -0.60 Ferredoxin (oxidized) 1 -0.43 2 H+ 2 -0.42 NAD+ 2 -0.32 NADP+ ΝADPH + H , 2 -0.32 Lipoate (oxidized) Glutathione (oxidized) Lipoate (reduced) Glutathione (reduced) 2 -0.29 2 -0.23 FAD FADH, 2 -0.22 Acetaldehyde Ethanol 2 -0.20 Pyruvate Lactate -0.19 2 H* H, 2 -0.00! Fumarate Succinate 2 +0.03 Cytochrome b (+3) Dehydroascorbate Cytochrome b (+2) 1 +0.07 Ascorbate 2 +0.08 Ubiquinone (oxidized) Cytochrome c (+3) Fe (+3) ½02 + 2 H* Ubiquinone (reduced) Cytochrome c (+2) Fe (+2) 2 +0.10 1 +0.22 1 +0.77 H,O 2 +0.82 2.
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