Microbial degradation of physiologically active peptides by strain B-9.

The reaction of some physiologically active peptides with bacterial strain B-9 has been investigated. Bradykinin, β-endorphin, and [Leu(5)]enkephalin were quickly degraded, with half-lives of <5 min. Somatostatin, substance P, and angiotensin I were degraded relatively smoothly, with half-lives of 10 min to 1 h, whereas oxytocin and insulin were slowly degraded, with half-lives of 1 and 4 days, respectively. Vasopressin was barely degraded, with a half-life of >7 days. Linearized vasopressin, prepared by the reductive cleavage of the disulfide bond followed by alkylation with iodoacetamide, was degraded significantly faster than intact vasopressin, with a half-life of 2.5 h. A loop formed by disulfide bond formation was regarded as one of the degradation-resistant factors. Hydrolysis of the peptides in this study took place through cleavage of various peptide bonds, and the strain B-9 may bear similarities to the neutral endopeptidase in terms of its broad selectivity.