Studies on the control of arginine hydrolysis in the liver of Merluccius gayi

1.1. The tissue content, subcellular localization and kinetic properties of arginase (l-arginine amidinohydrolase, EC 3.5.3.1) from the liver of the teleost fish Merluccius gayi, were investigated.2.2. The metal ion requirement of the enzyme was satisfied by Mn2+ and, to a much lower extent by Cd2+ and Co2+. The enzyme was markedly sensitive to inhibition by Zn2+.3.3. The optimum pH was 9.5 and the Km values for arginine were 1.7 and 10.3 mM at pH 9.5 and 7.5, respectively. These values were not altered in the temperature range of 9–37°C.4.4. The enzyme was markedly inhibited by branched chain amino acids and especially by isoleucine. A 50% inhibition was caused by 0.8 mM isoleucine, 2 mM leucine, 3 mM valine, 7.5 mM ornithine, 12 mM lysine or 22 mM proline.5.5. The enzyme was found localized in the mitochondrial matrix of the liver cells. It is suggested that the properties of arginase avoid an indiscriminate hydrolysis of argine and regulate the use of arginine as an energy source in the liver of M. gayi.