Masakazu Hoshi

Biosensor system for continuous flow determination of enzyme activities. I. Determination of glucose oxidase and lactic dehydrogenase activities

Abstract A biosensor system for continuous flow determination of enzyme activity was developed and applied to the determination of glucose oxidase and lactic dehydrogenase activities. The glucose oxidase activity sensor was prepared from the combination of an oxygen electrode and a flow cell. Similarly, the lactic dehydrogenase activity sensor was prepared from the combination of a pyruvate oxidase membrane, an oxygen electrode, and a flow cell. Pyruvate oxidase was covalently immobilized on a membrane prepared from cellulose triacetate, 1,8-diamino-4-aminomethyloctane, and glutaraldehyde. Glucose oxidase activity was determined from the oxygen consumed upon oxidation of glucose catalyzed by glucose oxidase. Lactic dehydrogenase activity was determined from the pyruvic acid formed upon dehydrogenation of lactic acid catalyzed by lactic dehydrogenase. The amount of pyruvic acid was determined from the oxygen consumed upon oxidation of pyruvic acid by pyruvate oxidase. Calibration curves for activity of glucose oxidase and lactic dehydrogenase were linear up to 81 and 300 units, respectively. One assay could be completed within 15 min for both sensors and these were stable for more than 25 days at 5°C. The relative errors were ±4 and ±6% for glucose oxidase and lactic dehydrogenase sensors, respectively. These results suggest that the sensor system proposed is a simple, rapid, and economical method for the determination of enzyme activities.

Microbial sensor system for nondestructive evaluation of fish meat quality

A microbial sensor system consisting of the bacterium (Alteromonas putrefaciens) immobilized within membranes, a flow cell, an oxygen electrode, peristaltic pumps, a buffer tank, a thermostatically controlled bath and a recorder, was constructed for the nondestructive quality evaluation of bluefin tuna. The chemical compounds on fish meat surfaces which are the indicators of fish meat quality were rapidly determined by using the proposed sensor system. Fish meat quality was determined from the rate of current decrease of the sensor. Good correlations were obtained between fish meat quality and sensor response. One assay could be completed within one minute.

Determination of dehydroascorbic acid by an enzyme sensor system with a parallel flow cell

Abstract An enzyme sensor system was developed for the determination of dehydroascorbic acid and L-ascorbic acid. The system was constructed from a parallel flow cell separated by a dialysis membrane, an immobilized ascorbate oxidase membrane, coupled to a Clark-type oxygen electrode, and L-cysteine, which was present as a reductant. The method is based on the reduction of dehydroascorbic acid to L-ascorbic acid with L-cysteine in a parallel flow cell. One assay for dehydroascrobic acid could be completed within 8 min. Linear calibration curves for dehydroascorbic acid and L-ascorbic acid were observed in the range of 20 mM–100 mM and 2 mM–20 mM, respectively.