Stereospecificity of peptidyl dipeptide hydrolase (angiotensin I-converting enzyme).

The stereospecificity of peptidyl dipeptide hydrolase [EC 3.4.15.1] was investigated. Six free and N-blocked alanyl peptides containing D-alanine were synthesized and tested as substrates. Their susceptibilities were determined by measuring Ala-Ala release by cation exchange column chromatography. Their Michaelis constants, Km values, and velocity maxima, Vmax values, were also determined. The enzyme showed high stereospecificity for an amino acyl residue in position 3 from C-terminus: it had an absolute requirement for the alanyl residue of the L-configuration in this position. An alanyl residue of the L-configuration in position 1 or 2 increased, but was not essential for activity. The enzyme showed little stereospecificity for an alanyl residue in position 4 from the C-terminus.