nize" both residues forming the bond. Moreover, when different peptides containing the same terminal bonds are compared, large differences in reactivity are observed. Thus, with LAP, Ala, (ldll) is not digested under our conditions, Ala3 (ldl) is digested in trace amounts only, and Ala, (lddl) is digested at an appreciable rate. Yet all three peptides contain the N-terminal LD-type bond. Additional examples of this kind can be found in Table III. This is an indication that not only the nature of the bond hydrolyzed determines its susceptibility to cleavage, but that residues further removed also exhibit an influence on the rate of enzymatic attack. Similar findings with respect to the action of CP-A on ll bonds have been described in a preliminary communication . It was shown by comparing kinetic rate constants that the enzyme "recognizes" at least four residues in the substrate. This was deduced from the observation that the C-terminal bonds of the three tetrapeptides llll, dlll, and ldll are split at relative rates of about 100:10:1. Other proteolytic enzymes seem to behave in a similar manner. Papain was shown to interact simultaneously with five residues in the substrate . Results obtained re-cently in this laboratory indicate that trypsin and aspergillopeptidase B (Subramanian and Kalnitsky, 1964) recognize a sequence of five and seven residues, respectively, in a peptide chain.

No abstract

No abstract

No abstract