KINETICS AND INHIBITION BY SOME AMINO-ACIDS OF LACTATING RAT MAMMARY-GLAND ARGINASE

Some kinetic and regulatory properties of lactating rat mammary gland arginase were studied. At pH 7.4, i.e. at near-physiological condition s, there was evidence of inhibition by excess of substrate, with a K-m value of 9.5 mM, slightly lower than the value of 18 mM observed at p H 9.8 (maximum enzyme activity). A study was also made of the effects of proline, ornithine, lysine and certain branched-chain aminoacids on enzyme activity : lactating rat mammary gland arginase was strongly a nd competitively inhibited by lysine, ornithine and valine, with Ki va lues of 1.2 mM, 1.1 mM and 3.6 mM, respectively. Other aminoacids (pro line, isoleucine and leucine) also inhibited lactating rat mammary gla nd arginase, although to a lesser extent.