[Conformational aspects of peptide interaction with proteolytic enzymes. Effect of amino acid residue configuration on binding of stereoisomeric N-acetylleucyltyrosine and N-acetyltyrosylleucine methylamides with pepsin].

Ki, Km and kcat. constants which characterize the interaction with pepsin of a complete series of Ac-Leu-Tyr-NHMe and Ac-Tyr-Leu-NHMe stereoisomers are determined. In compounds, containing residues of different configuration, Ki was found to have higher values than Ki or Km in DD- and LL-dipeptides. The data obtained show that not only the rate of peptide bond hydrolysis but also the efficiency of the binding with the enzyme depend on the configuration of the amino acid residue. Differences in the efficiency of pepsin binding of diastereomers is a manifestation of differences in their conformational characteristics. Data on "secondary" binding sites of pepsin are used to account for a mixed type inhibition observed in some cases.