GAMMA-GLUTAMYL-TRANSFERASE ACTIVITY IN HUMAN PLATELETS - QUANTIFICATION OF ACTIVITY, ISOENZYME CHARACTERIZATION AND POTENTIAL CLINICAL RELEVANCE

Gamma-glutamyltransferase (GGT) activity in human platelet sonicates w as 13.6 u/g of protein (range: 7.9-25.0) in 13 healthy, non-smoking, f emale volunteers; corresponding values in 16 males were: 20.3 (10.1-26 .0), These values differed significantly (p = 0.034). Platelet and ser um GGT activity correlated significantly (p < 0.04). Platelets seem to contain only the isoenzyme GGT 4, Part of this enzyme activity is in the form of aggregates or linked with membranes/proteins. This activit y is released by Triton X-100 and trypsin and migrates as GGT 4, Serum GGT activity, a measurement in routine use, could be influenced by GG T released by platelets, It is therefore of interest that serum GGT ac tivity can be increased in clinical conditions (e,g, myocardial infarc tion, diabetes, peripheral vascular disease) associated with platelet hyperactivity, Platelet GGT may influence intracellular S-nitrosogluta thione (a putative nitric oxide donor) levels, Potential associations between serum GGT activity and platelet function indices deserve inves tigation.