Leupeptin and chymostatin inhibit mammalian protein methylesterase activity

Abstract

Purified protein methylesterase (PME) from rat kidneys was incubated with ovalbumin-methyl esters and a series of protease inhibitors. All four inhibitors with C-terminal aldehyde, leupeptin, chymostatin, Boc-Gln-Leu-Lys-H and D-Phe-Pro-Arg-H completely blocked PME activity. Other inhibitors including, ∝ - 1 antitrypsin, soybean trypsin inhibitor, antithrombin III, phenylmethylsulfonylfluoride, aprotinin and limabean trypsin inhibitor had no significant effect whereas pepstatin, at high concentration reduced the enzymatic activity by 25%. The most potent inhibitors, leupeptin and chymostatin, had a Ki of 3.5 × 10 −8 and 5.4 × 10 −7 M, respectively. These inhibitors provide two new tools to study PME function.