Cecile Schattenkerk

Peptide substrates for chymosin (Rennin). Kinetic studies with peptides of different chain lenght including parts of the sequence 101–112 of bovine κ-casein

Kinetic parameters have been determined for the reaction between milk-clotting chymosin (EC 3.4.23.4) and a series of peptides (or their methyl esters) including the amino acid sequence around the enzyme-sensitive Phe(105)-Met (106) bond the bovine k-casein. In particular, the influence of the substrates chain length on the kinetic parameters has been studied. Evidence is presented that in the model peptides studied the sequence -Ser-Phe-Met-Ala with a further residue added to either end (in casu Leu(103) or Ile(108)) is necessary to induce any cleavage by the enzyme. When both the Leu(103) and Ile(108) residues form part of the peptide chain, a marked improvement of the substrate properties is observed. It is suggested that prolyl residues on either side of the sensitive peptide bond form additional sites for secondary enzyme-substrate interactions.

Peptide substrates for chymosin (Rennin) Kinetic studies with bovine κ-casein-(103–108)-hexapeptide analogues

Kinetic parameters have been determined for the reaction between chymosin (EC 3.4.23.4) and synthetic peptide analogues of the sequence Leu-Ser-Phe-Met-Ala-Ile around the chymosin-sensitive Phe(105)-Met(106) bond of bovine kappa-casein. From the present and earlier results it is concluded that a minimum length of the molecular backbone with three amino acid units on both sides of the scissile bond is required to make the peptide a good substrate for the enzyme. In addition, hydrophobic side chains in the positions 103 and 108, and particularly the hydroxyl group of Ser-104 contribute to the effectiveness of the enzyme-substrate interactions. The substrate properties are markedly influenced by changes in the steric and/or polar character of the amino acid side chains in the positions 105 and 106.

SYNTHESIS AND ACTIVITY OF ANGIOTENSIN ANALOGUES (MOSTLY HEPTAPEPTIDES) IN WHICH THE ARGININE MOIETY IS REPLACED BY SIMILAR RESIDUES OF VARIED STRUCTURE AND CONFIGURATION

Publisher Summary This chapter discusses the synthesis and activity of angiotensin analogues—mostly heptapeptides—in which the arginine moiety is replaced by similar residues of varied structure and configuration. The structure of the natural octapeptide is Asp-Arg-Val-Tyr-Ile-His-Pro-Phe. The heptapeptide obtained by omitting the first amino-acid residue is considerably active. However, the hexapeptide differing from the heptapeptide by lack of the basic arginine molecule has a strongly reduced activity. The positive charge at the end of the chain of the arginine residue of the heptapeptide plays a role in the binding of the molecule onto a certain receptor or in catalyzing a certain reaction. Factors, such as length and flexibility of the chain bearing the positive charge, can determine the ease and probability for the charged grouping to occupy the right position. Besides the guanidinium or ammonium group at the end of the side-chain, there is also present an α-NH3 group in the peptides. For good activity, the two positive charged groups must each occupy a definite position. This can be easily achieved with a terminal D-amino-acid residue than with its mirror image.