Electrochemical and Raman spectroscopic studies of the effect of lanthanide ions on the activity of mitochondrial malate dehydrogenase

Chronoamperometry based on the ‘diffusion’ layer concept of the convective system was used to assay the activity of mitochondrial malate dehydrogenase (MDH). When the enzyme-catalysed reaction was initiated by adding the enzyme MDH into a well-stirred nicotinamide adenine dinucleotide (NADH, coenzyme) solution, the enzyme activity could be indicated by the continuous in-situ decrease in the limiting steady-state oxidation current of NADH. The effects of some lanthanide ions on the MDH activity were monitored. The La3+, Ce3+ and Eu3+ ions could activate markedly the enzyme MDH as the concentrations were lower. The activation mechanism would be that the lanthanide ions could interrupt the binding of NAD+ to MDH by combining preferentially to NAD+. This mechanism was proposed on the basis of voltammetric and Raman spectroscopic studies.