Preparation and analysis of peptide fragments produced by pepsin hydrolysis of human plasma albumin and their relationship to its structure.

Human plasma albumin was prepared and subjected to proteolysis by pepsin at pH2.45 at 25 degrees for 10min. with albumin/pepsin ratio 3000:1. Five peptide fragments were detected in the proteolysate by means of zone electrophoresis and gel filtration; these were separated and purified. Molecular weights, amino acid composition and disulphide bond content of the purified fragments were determined. The results show that a high proportion of the polypeptide chain of albumin appears to have a low cystine content, and at low pH values the molecule would be expected to have a considerable degree of freedom in its structure in these regions of the chain. A tripartite model for the structure of plasma albumin is proposed.