Comparative Studies on Four Sulfhydryl Endopeptidases ("Ficins") of Ficus glabrata Latex

Five sulfhydryl endopeptidases were purified to homogeneity from commercial preparations of Ficus glabrata latex. One of these corresponded to ficin isolated from the same source by Englund, King, Craig, and Walti (Biochemistry, 7, 163 (1968)). Each of these enzymes appeared to consist of a single polypeptide chain, of 25,000 to 26,000 molecular weight, with amino-terminal leucine. They displayed very similar specificity and kinetic properties towards the B chain of oxidized insulin, casein, and synthetic ester substrates. The enzymes showed differing retention behavior on cation exchangers, different mobilities in polyacrylamide gels, reproducible differences in amino acid composition, particularly in the content of arginine and tyrosine, and distinct peptide maps. The tryptic peptide maps strongly suggest that these enzymes share a high proportion of common regions in their amino acid sequences. They do not appear to arise by cleavage of a common precursor.