A bienzyme electrode for L-malate based on a novel and general design.

The coimmobilization of a NAD(P) + -dependent dehydrogenase with salicylate hydroxylase (SHL, EC 1.14.13.1) in front of a Clark-electrode yields a flexible new design for dehydrogenase based biosensors. The feasibility of the approach has been tested with malic enzyme (MDH, EC 1.1.1.40) as the dehydrogenase, resulting in a novel L-malate sensor. It had substantial advantages over the biosensor approaches reported earlier: effective re-oxidation of NADPH by SHL yielded an extended linear range from 0.01 to 1.2 mmol 1(-1) L-malate and strongly reduced NADP+ -requirement (<0.025 mmol 1(-1)), while the working stability was increased to more than 30 days. The results obtained from six real samples showed a close correlation with the standard enzymatic method. The presented scheme with SHL and the Clark-electrode can be employed together with any NAD(P)+ -dependent dehydrogenase.