Electrochemical determination of γ-glutamyl transpeptidase activity and its application to a miniaturized analysis system

A novel method to determine the activity of γ-glutamyl transpeptidase (γ-GTP) was developed. γ-l-glutamyl-l-glutamate and glycyl-glycine were used as the substrates for γ-GTP. l-glutamate produced by the enzymatic reaction was measured with an amperometric l-glutamate sensor. Following the mixing of the substrate solution and a sample solution, the current generated on the l-glutamate sensor continued to increase at a constant rate. The method was used to construct a miniaturized analysis system for the determination of γ-GTP activity. The system consisted of the l-glutamate sensor formed on a glass substrate and a polydimethylsiloxane (PDMS) flow channel. Since the l-glutamate concentration in the solution increased as the solution was mobilized through the flow channel, a constant current increase was observed. The relation between the slope of the response curve and the activity of γ-GTP was linear between 35 U l−1 and 659 U l−1. The rate analysis in the micro flow channel minimized the influence of interferents. The reproducibility of the output of the micro system was found to be good with a relative standard deviation (R.S.D.) of 5.6% at 659 U l−1. The activities of γ-GTP in human serum samples were also determined and compared with values obtained with a conventional spectroscopic method. The values obtained by the two methods were consistent with a correlation coefficient of 0.953.