[Influence of temperature on enzyme activity determination in serum : L-aspartate aminotransferase isoenzymes]

The influence of temperature on activity assays of the isoenzymes of L-aspartic aminotransferase in described. For this purpose, isolated human isoenzymes were added to inactivated serum. Half-saturation constants were determined at 17.8 degrees C, 25 degrees C, 30 degrees C, and 37 degrees C, and the substrate saturation and pH curves were recorded. The cytoplasmatic (c) and mitochondrial (m) GOT showed temperature-dependent differences in the half-saturation constants for the substrates L-aspartate and 2-oxoglutarate. For both isoenzymes pH 7.4 is considered the optimum regardless of the temperature of measurement, and Tris-HCl is the optimal buffer. In the Arrhenius plot there is a bent at 27 degrees C for both isoenzymes. Thermal denaturation as a possible reason for this deviation from the linearity in the Arrhenius plot could be ruled out.