Biodegradability of Synthetic Branched Polypeptide with Poly(L-lysine) backbone

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Abstract
A detailed investigation is reported about the biodegradation of poly[Lys(DL-Alam)], m .apprx. 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 M, or the endopeptidase trypsin, on 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.