[The role of peripheral interactions in chymosin specificity]

Kinetic parameters for the splitting of model peptide substrates and chi-casein with chymosin have been interpreted on the basis of the three-dimensional structure of chymosin. Model peptide substrates contain a fragment of the chi-casein sequence in the region of the bond Phe-105--Met-106 splitted with the enzyme. It was shown that the possible reason of the enormous milk-clotting efficiency of chymosin may be partly associated with the electrostatic interaction of the positive charged segment 98-102 (His-Pro-His-Pro-His) of the substrate and outer loop of the enzyme which contains Glu-245, Asp-247, Asp-249, Asp-251.