Abstract

Ethyl D-cysteinate is a potent competitive inhibitor (K_i = 3.5 × 10^--⁷M) of aminopeptidase M. D-cys-teine and ethyl L-cysteinate inhibit more than two orders of magnitude less effectively. Inhibition studies on several n-alkyl esters of D-cysteine reveal an optimum at the n-butyl ester (K_i = 1.8 × 10^--⁷M). The results are consistent with the hypothesis that the thiol group coordinates to Zn⁺² at the active site and the alkyl group occupies the hydrophobic binding site for the side chain of the amino-terminal residue of substrates. Cytosolic leucine aminopeptidase is not significantly inhibited by ethyl D-cysteinate.