Lactate dehydrogenase catalyzes the reversible reaction: Pyruvate + NADH + H + L

ID: 180052 • Letter: L

Question

Lactate dehydrogenase catalyzes the reversible reaction:

Pyruvate + NADH + H+ Lactate + NAD+

The relevant half-reactions are:

NAD+ + H+ + 2e– à NADH E'° = –0.32 V

pyruvate + 2H+ + 2e– à lactate E'° = –0.19 V

A. In the overall reaction, indicate which species is being oxidized and which is being reduced.

Oxidized: ___________________________________

Reduced: ___________________________________

B. Calculate G'° for this reaction.

C. Calculate G for this reaction at standard temperature when [pyruvate] = 1 M, [lactate] = 0.1 mM, [NADH] = 1 M, and [NAD+] = 0.1 mM.

The oxidation half-reactions are:

lactate => pyruvate + 2 H+ + 2 e–, E°' = +0.190 V

NADH + H+ => NAD+ + 2 H+ + 2 e–, E°' = +0.320 V

The reaction with the more positive E°' is favored

calculation G'° for this reaction

:NAD+ + H+ + 2e– NADH E'° = –0.32 V

pyruvate + 2H+ + 2e– lactate E'° = –0.19 V

The Faraday constant, , is 96.48 kJ/V·mol.

Ans:

G'° = E'°(acceptor) – E'°(donor) = –0.19 V – (–0.32 V) = +0.13 V

G'° = –n E'° = (–2)(96.48 kJ/V·mol)(0.13 V)

G'° = –25.1 kJ/mol--------------answer

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