Measurement of L-Malate Using Immobilized Enzyme Reactors: Comparison of Results Obtained with Four Different Enzymatic Systems.

Abstract

For the measurement of malate by an enzyme sensor, we did a comparative study using malate dehydrogenase (MDH) alone, MDH and glutamate oxaloacetate transaminase (GOT) together, a malic enzyme (ME) that requires NADP as a cofactor, and MDH and NADH oxidase together. With respect to the response of each reactor to 0.5 mM L-malate, the systems using ME alone and MDH plus NADH oxidase gave high values. The ranges of measurements were 0.05-1.00 mM (MDH alone), 0.01-0.05 mM (MDH plus GOT), 0.01-0.50 mM (ME alone) and 0.02-1.00 mM (MDH plus NADH oxidase). In the system with MDH alone, however, reducing sugars in the sample interfered with measurements and it was impossible to use this system for practical analysis of fruit samples. By contrast, the systems using ME alone or MDH plus NADH oxidase were unaffected by the presence of reducing sugars and were suitable for analysis of samples. Thus, the MDH-NADH oxidase system is recommended for practical analyses of samples.