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New Chromophoric Peptide Substrates for Chymosin (Rennin)

Equipe de Recherche n°15 CNRS, Institut de Biochimie Universite Paris-Sud, 91405 Orsay Cedex France

¹ To whom requests for reprints should be addressed.

ABSTRACT

Kinetic studies on the hydrolysis by chymosin (rennin) of the chromophoric hexapeptide substrates-. H-Leu-Thr-Phe(NO₂)-Nle-Ala-Leu-OMe, H-Leu-Ala-Phe(N0₂)-Nle-Ala-Leu-OMe, and H-Leu-D-Ser-Phe(N0₂)-Nle-Ala-Leu-OMe allow us to conclude that the (ß-OH group of Ser₁₀₄ residue of the physiological substrate (k-casein) is involved in the interactions between chymosin and its substrates. To contribute to effectiveness of these interactions the seryl residue has to be in the L-configuration

Kinetic studies of the hydrolysis of penta-, hexa-, hepta-, and octapeptide substrates, the structures of which are close to the sequence around the Phe₁₀₅-Met₁₀₆ bond of k-casein, show that elongation of the peptide chain produces a significant increase of the rate of hydrolysis of the sensitive bond. The best substrate synthesized is the octapeptide: H-Pro-His-Leu-Ser-Phe(N₂)-Nle-Ala-Leu-OMe.

The study of the effect of pH on the kinetic parameters of the hydrolysis of the hexapeptide H-Leu-Ser-Phe(NO₂)Nle-Ala-Leu-OMe shows that the
ratio is dependent on the ionization of two carboxyle groups of the enzyme, the pK of which are 3.3 and 5.7.

Comparative study of the hydrolysis of H-Leu-Ser-Phe(N0₂)-Nle-Ala-Leu-OMe and H-Leu-Ala-Phe(N0₂)-Nle-Ala-Leu-OMe by chymosin, bovine, and porcine pepsins also is reported.