Catalyzes the conversion of L-arginine into 2-ketoarginine via transamination. L-arginine is the best substrate, but it can also use L-lysine, L-methionine, L-leucine, ornithine and L-glutamine, which indicates that it may have a broader physiological function in amino acid catabolism. L-arginine + pyruvate = 5-guanidino-2-oxopentanoate + L-alanine kcat is 38.6 sec(-1). Optimum pH is 9.0. Optimum temperature is 42 degrees Celsius. Amino-acid degradation; L-arginine degradation. Homodimer. Induced by L-arginine in the absence of ArgR, via the AruR/AruS two-component regulatory system. Belongs to the class-I pyridoxal-phosphate-dependent aminotransferase family.