Studies on Human Serum β1-Lipoprotein

Abstract 1. Exhaustive digestion of native human serum β1-lipoprotein by either trypsin or pronase resulted in the hydrolysis of only a fraction of the potentially susceptible peptide bonds. However, hydrolysis of the lipid-free protein by these enzymes was more nearly complete. 2. Peptide maps of the products of tryptic digestion indicated that a specific segment of the polypeptide chain of the native molecule was attacked. This was supported by the observation that the amino acid composition of the soluble products resulting from either tryptic or pronase digestion differed significantly both from the parent molecule and from the residual large polypeptide component. 3. The histidine residues present in the segments attacked by trypsin or pronase were also those which were most readily modified by chemical reagents.