Specificity of a cysteine proteinase of Entamoeba histolytica against various unblocked synthetic peptides.

The activity of highly purified cysteine proteinase of Entamoeba histolytica against different peptides of the sequence X-Gly-Phe-Phe was compared. The synthetic peptide Arg-Gly-Phe-Phe of the insulin B-chain was readily hydrolyzed yielding Arg-Gly and Phe-Phe as split products. Lys-Gly-Phe-Phe and Tyr-Gly-Phe-Phe were cleaved at rates of 20 and 4%, respectively. Val-Gly-Phe-Phe, Gly-Gly-Phe-Phe, Glu-Gly-Phe-Phe, and Ser-Gly-Phe-Phe were hydrolyzed at rates far below 1%. Gly-Arg-Phe-Phe, Gly-Phe-Phe, and Gly-Phe were completely resistant to the enzyme. Another good substrate was found in Arg-Gly-Leu-Hyp, which represents a model compound of a scissile site in collagen type I. Furthermore, peptide Arg-Arg-Phe-Phe was attacked by the enzyme releasing Arg-Arg and Phe-Phe. Compared with Arg-Gly-Phe-Phe at substrate concentrations of 2 mM the rates of hydrolysis of Arg-Arg-Phe-Phe and Arg-Gly-Leu-Hyp were 37 and 127%. The enzyme exhibited dipeptidyl peptidase activity against the nonapeptide Arg-Gly-Phe-Phe-Tyr-Thr-Pro-Lys-Ala releasing Arg-Gly.