magine that in a metabolic pathway, one of the steps involves the oxidation of s

Question

magine that in a metabolic pathway, one of the steps involves the oxidation of saturated compound to an unsaturated compound, with the concomitant reduction of the cofactor FAD to FADH2 as shown below: R-CH2-CH2-R' + FAD <----> R-CH=CH-R' + FADH2 Imagine further that G°´ for this reaction is 0 kcal/mol. Given this scenario, what would be the equilibrium concentration of FADH2 (expressed in mM to the nearest tenth of a unit) if a biochemist started with a solution that contained 0.01 M each of R-CH2-CH2-R', FAD, and FADH2 (but no R-CH=CH-R'), along with 20 nM concentration of the enzyme that catalyzes the reaction?

Explanation / Answer

R-CH2-CH2-R' + FAD <----> R-CH=CH-R' + FADH2

G° = -RTlnKeq = 0

or, Keq = 1

or, [R-CH=CH-R'][FADH2]/[R-CH2-CH2-R'][FAD] = 1

suppose at equilibrium [[R-CH=CH-R] = [FADH2] = x

x * (0.01 + x)/ (0.01-x) ^2 = 1

or, x^2 + 0.01x = 0.0001 - 0.02x+x^2

or, 0.03x = 0.0001

or, x =0.0033

[FADH2] = 0.01 + 0.0033 = 0.0133 M

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