Amino acid sequence of chymotrypsin inhibitor ECI from the seeds of Erythrina variegata (Linn.) var. Orientalis.

The amino acids of the chymotrypsin inhibitor (ECI) from the Erythrina variegata seeds have been sequenced. The sequence was solved by analysis of peptides derived from the protein by enzymatic digestions with trypsin and Staphylococcus aureus V8 proteinase, as well as by chemical cleavage with o-iodosobenzoic acid. The ECI consists of 179 amino acid residues with a pyroglutamic acid as the N-terminal residue and has a calculated molecular weight of 19,791. Comparison of this sequence with the sequences of the two trypsin inhibitors, ETIa and ETIb, from the E. variegata seeds shows that about 60% of the residues of ECI are identical to those of ETIa and ETIb and that the reactive sites, Arg63, in ETIa and ETIb change to Leu64 in ECI.