Amino acid sequence of lima bean protease inhibitor component IV. 1. Isolation and sequence determination of the tryptic peptides.

Abstract

Commmerical lima bean inhibitor was fractionated into four apparently homogeneous components as previously described by Jones, Moore and Stein in 1963.Reduced and alkylated component IV was hydrolyzed with tryspin and the resulting peptides were separated by ion exchange charomatography on Dowexs 50 X2 or gel filtration on Bio‐Gel P‐6. Where necessary, further purification of the peptides was carried out by paper chromatography, paper electrophoresis or a combination of both.Seven peptides were obtained in pure form and their compositions are reported here. The amino acid sequenceof six of these peptides was determined, using classical methods. When allowance is made for the occurence of two homologous peptides, presumably resulting from heterogeneity in the original protein preparation, the tryptic peptides isolated, account for the complete composition of the protein.In an attempt to obtain overlapping sequences the tryptic digest was also performed on the reduced, alkylated and guanidinated protein. Five tryptic peptides, including one containing homoarginine as the carboxy‐terminal residue, were isolated in pure form from the digest; their amino acid compositions are reported.