gamma-Aminobutyrate aminotransferase activity in blood platelets of six species

1. The kinetic parameters of gamma-aminobutyrate aminotransferase (GABA-T) were studied in washed blood platelets from cat, dog, horse, man, mouse and rat. 2. Wide differences were found in the maximal reaction velocity (Vmax) of GABA-T in blood platelets of the six species. 3. A significant increase in the activity of GABA-T was found in the blood platelets of adult rats as compared to those of young rats. 4. However, there was no significant difference in the activity of platelet GABA-T between male and female rats. 5. The activity of human platelet GABA-T estimated in platelet-rich plasma from healthy male subjects was found to be decreased in the presence of plasma and albumin. 6. The decrease was due to the specific binding of the cofactor pyridoxal phosphate to plasma albumin.