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

The coimmobilisation 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 l(-1) L-malate and strongly reduced NADP(+)-requirement (< 0.025 mmol l(-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. (C) 1998 Elsevier Science B.V. All rights reserved.