Biodegradability of synthetic branched polypeptide with poly(L-lysine) backbone

A detailed investigation is reported about the biodegradation of poly[Lys(DL-Alam)], m approximately 3, (AK) the common inside area of a branched polypeptide model system developed by our group over the last decade. Enzymatic hydrolysis was carried out by the exopeptidase aminopeptidase M, or the endopeptidase trypsin, or their mixture. Ion-exchange column chromatography, paper electrophoresis and thin-layer chromatography were utilised to achieve separation of metabolites. Breakdown products were identified by the aid of synthetic oligopeptides representing the potential fragments (DL-Ala2, DL-Ala3, Lys(DL-Alam), m = 1-3). The kinetics and the degree of enzymatic degradation were determined. The ratio of peptide/amino acid amounts in the hydrolysate was found to be 1.07 after 24 h treatment with aminopeptidase M, 3.0 with trypsin and 1.3 with aminopeptidase - trypsin mixture. The overall results indicated that the proteolysis of AK by an aminopeptidase M and trypsin mixture proceeds stepwise at multiple sites on the polypeptide chain. The degradation is significantly retarded as compared to that of alpha- or epsilon-polylysine. A mechanism of degradation is suggested based on the experimental results.