Determination of Activities of Lactate Dehydrogenase and α-Hydroxybutyrate Dehydrogenase in Serum Using a Membrane-Covered Plastic Formed Carbon Electrode

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A newly developed plastic formed carbon electrode (PFC electrode) produced a reproducible anodic current due to the oxidation of NADH at potentials less positive than those required by ordinary electrodes such as glassy-carbon electrodes. A dialysis membrane-covered PFC electrode produced steady-state currents linearly proportional to concentrations of NADH ranging from 5 to 1500μmol/l. The within-day variation for measurements was 3.1% for five runs at an NADH concentration of 100μmol/l. Activities of lactate dehydrogenase (LDH) and α-hydroxybutyrate dehydrogenase (HBD) in serum were determined by measuring the decrease in current due to oxidation of NADH for 3 min at 400mV and 37°C in Tris buffer of pH 7.5 containing 350μmol/l NADH and 2 mmol/l pyrurate, or 4 mmol/l α-ketobutyrate. Serum was diluted to yield a concentration one-fifteenth that of the sample. Measurements of activities obtained using this method agreed well with those obtained using UV method (r=0.993, of LDH and HBD n=15 for LDH; r=0.999, n=15 for HBD).