Some kinetic characteristics of erythrocyte alanine aminotransferase phenotypes

The activity of alanine aminotransferase (ALT) phenotypes was determined in 148 hemolysates of the Serbian population. The highest activity was obtained for phenotype ALT 1 (0.614 U/g Hb), intermediate for ALT 2-1 (0.475 U/g Hb), and the lowest for ALT 2 (0.395 U/g Hb). To explain the differences in catalytic activity between the ALT phenotypes, some kinetic characteristics were investigated. No difference in heat stability and calculated activation energies for ALT phenotypes could be detected. Addition of pyridoxal 5'-phosphate to the reaction system did not increase the catalytic activity. For the catalytic activity of all three phenotypes, a broad pH optimum in the range 7.1 to 7.6 was found. The Tris/HCl buffer concentration of 140 mmol/liter was optimal. The Michaelis-Menten constants for L-alanine as substrate were 2.462 mmol/liter for ALT 1, 1.965 mmol/liter for ALT 2-1, and 2.698 mmol/liter for ALT 2. For another substrate, 2-oxoglutarate, Km values were 0.299, 0.208, and 0.202 mmol/liter, respectively.