New colorimetric micromethod for the estimation of gamma-glutamyl transpeptidase activity in biological samples.

A new colorimetric micromethod for the estimation of y-glutamyl transpeptidase activity has been developed, in order to obtain more reliable results with greater ease on smaller samples of a wider variety. Enzyme activity can be determined on 0.1 m/ of serum or less, or the equivalent of spinal fluid or tissue extracts, because the precipitation of proteins has been omitted. Therefore, correction for possible losses of the reaction product, -naphthylaminc, is no longer necessary and the chromogen can be diluted without the risk of turbidity, thus permitting the estimation of very low, as well very high enzyme activities. The method utilizes 2 different substrates, designed to determine peptidase and transpeptidase activity, respectively, the differentiation of which is of empirical significance. The clinical results suggests that y-glutamyl transpeptidase is a common name for a group of enzymes, some of which occur in an insoluble microsomal form, others in a soluble form. There is good evidence that the increased activation by glycylglycine is the result of an increased conversion of the microsomal enzyme to the soluble form and that the transpeptidation activity increases more readily than the peptidase.