Specificity of papain-catalyzed transamidation reactions.

In the experiments reported in the present communication, these studies have been extended with special reference to the specificity of the enzyme toward the dipeptide used as replacement agent. It had been suggested (1) that the value of pKz’ of a dipeptide is a determining factor in the efficiency with which it can participate in a transamidation reaction at ‘a given pH. This suggestion has been examined by the determination of pK2’ for several dipeptides under the conditions of the enzymic tests and the comparison of the relative magnitude of these values with the observed efficiency of transamidation. Earlier data (1) had also indicated that, in addition to the pKz’ values, other factors that are important in determining the efficiency of a dipeptide as a replacement agent are the chemical nature of the R’ group and the configuration of the N-terminal amino acid residue. This aspect of the problem was investigated further by the use of a variety of dipeptides.