Catalyzes the epimerization of L-isoleucine to D-allo-isoleucine and D-allo-isoleucine to L-isoleucine. Can also catalyze the racemization of many nonpolar amino acids, including leucine and valine. Does not have GABA aminotransferase activity. L-isoleucine = D-allo-isoleucine kcat is 502 sec(-1) with L-isoleucine as substrate. kcat is 939 sec(-1) with D-allo-isoleucine as substrate. Optimum pH is 5.0 for the forward reaction, and 6.0 for the reverse reaction. Optimum temperature is 50 degrees Celsius for the forward reaction, and 45 degrees Celsius for the reverse reaction. Homotetramer. Belongs to the class-III pyridoxal-phosphate-dependent aminotransferase family.