GSSG + NADPH + H+ 2GSH + NADP+ (a) Calculate G for the glutathione reductase reaction in the direction shown, using E values from

GSSG + NADPH + H+ †’ 2GSH + NADP+
(a) Calculate ˆ†G°€² for the glutathione reductase reaction in the direction shown, using E°€² values from Table 14.1.
(b) Suppose that a cell contained an isoform of glutathione reductase that used NADH instead of NADPH as the reductive coenzyme. Would you expect ˆ†G°€² for this enzyme to be higher, lower, or the same as the corresponding value for the real glutathione reductase? Briefly explain your answer.
(c) Given what you know about the metabolic roles and/or intracellular concentration ratios of NAD+ /NADH and NADP+ /NADPH, would you expect ˆ†G (not ˆ†G°€²) for this enzyme to be higher, lower, or the same as ˆ†G for the real enzyme under intracellular conditions? Briefly explain your answer.

TABLE 14.1 Standard reduction potentials of interest in biochemistry Oxidant Acetate CO2 2H 2e Succinate+ CO2+ 2H+ + 2e- Acetate 3H+2e Femedoxin (oxidized e 2H 2e -Ketoglutarate+ CO2+ 2H+2e Acetoacetate 2H2e Pyruvate CO2H 2e NAD + + H+ + 2e- NADPt H+ 2e Lipoate (oxidized)2H 2e 1,3-Bisphosphoglycerate 2H 2e Glutathione (oxidized)+ 2H+ + 2e- FAD (free coenzyme)2H 2e Acetaldehyde 2H +2e Pyruvate2H 26 oxaloacetate + 2H + + 2e- Reductant Pyruvate H20 a-Ketoglutarate H20 Acetaldehyde H2O Femedoxin (reduced) E" (V) -0.70 -0.67 -0.60 0.43 -0.42 -0.38 -0.35 -0.33 -0.32 0.32 -0.29 -0.29 -0.23 -0.22 -0.20 -0.19 lsocitrate B-Hydroxybutyrate Malate NADH NADPH Lipoate (reduced Glyceraldehyde-3-phosphate P 2 Glutathione (reduced) FADH2 Ethanol Lactate Malate 2 2 Oz (superoxide) Glutamate H2O FADH2 (enzyme-bound) -0.16 O2+ e a-Ketoglu FAD (enzyme-bound) 2H 2e Methylene blue (oxidized)+ 2H+ + 2e Fumarate2H+2e tarate NH4 2H 2e 2 -0.14 0 to -0.30 0.01 0.03 0.04 0.06 0.07 0.23 0.25 0.29 0.30 0.36 0.42 0.55 0.77 0.82 ethylene blue (reducea Succinate QH2 Ascorbate Cytochrome b (+2) Cytochrome c1(+2) Q2H2e Dehydroascorbate2H 2e Cytochrome b (+3) e Cytochrome ci(+3) e Cytochrome c (+3e Cytochrome a (+3)e 02 2H+ + 2e- Fericyanide2e NO3 (Nitrate) 2H2e Cytochrome a2(+3)e Fe (+3)e O22H2e 2 Cytochromec (+2) Cytochromea (+2) H202 Ferocyanide NO2 (Nitrite)+H2O Cytochrome a (+2) Fe(+2) H2O 2 2