Yukio Shimura

Kinetic assay of enzymes with an ammonia gas-sensing electrode : Part 1. Dynamic responses of the sensor

Abstract The input-response relationship of an ammonia gas-sensing electrode was studied with special emphasis on its potential application to kinetic assay of enzyme activity. The transfer function of the electrode was determined from stepwise changes in sample ammonia concentration. A mathematical expression for the electrode response to a linear increase in ammonia concentration (a simulated signal for an enzyme reaction under zero-order conditions) was derived. This expression showed reasonable agreement with xperimental results. Optimal conditions for enzyme activity determinations are discussed.

Kinetic assay of enzymes with an ammonia gas-sensing electrode : Part 2. In situ monitoring of serum leucine aminopeptidase

Abstract A kinetic assay for serum leucine aminopeptidase with an ammonia gas sensor is described. The time course of ammonia formation in the reaction, l -leucine amide → l -leucine + NH 3 is directly monitored by the sensor under zero-order kinetic conditions. The initial total ammoniacal concentration in the sample was adjusted to 50 μM to keep the response at a sufficiently high level for accurate monitoring. The reaction rates determined agreed with those found by a conventional method to within 6%.