Conceptual Error in Determination of NAD+-Malic Enzyme in Extracts Containing NAD+-Malic Dehydrogenase 1

AUTOR(ES)

Outlaw, William H.

RESUMO

The typical procedure for determining NAD+-malic enzyme (EC 1.1.1.39) is to calculate the enzyme rate to be ΔA340/Δ time after the endogenous NAD+-malic dehydrogenase (EC 1.1.1.37) catalyzed reaction has reached equilibrium. This ignores the equilibrium shift of oxaloacetic acid and NADH during the course of the NAD+-malic enzyme reaction and causes an error that varies depending on the reagent [malate], [NAD+], pH and final [NADH]. For a ΔA340 of 0.02, the error is about 80% and for a ΔA340 of 0.30, 20%. We develop this argument, give supportive data and present a simple method to circumvent the error.

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