title: Double-headed protease inhibitors from black-eyed peas. I. Purification of two new protease inhibitors and the endogenous protease by affinity chromatography.
abstract: Two new double-headed protease inhibitors have been isolated from black-eyed peas. The isoinhibitors can be purified to homogeneity with greater than 90% recovery in a four-step procedure by means of sequential affinity chromatography on trypsin-Sepharose and chymotrypsin-Sepharose affinity columns. The isoinhibitors both have molecular weights near 8,000 and both have the same NH1-terminal residue serine. Black-eyed pea chymotrypsin and trypsin inhibitor (BEPCI) has an isoelectric point of 5.1 and inhibits trypsin and chymotrypsin simultaneously. Black-eyed pea trypsin inhibitor (BEPTI) has an isoelectric point of 6.5 and inhibits 2 molecules of trypsin simultaneously. BEPTI binds to chymotrypsin-Sepharose above pH 6 but does not inhibit chymotrypsin in the standard inhibitor assay with 10-3  M substrate. These new inhibitors are distinct from the Ventura inhibitor isolated from Serido black-eyed peas. An endogenous seed protease has been isolated from black-eyed peas by affinity chromatography on soybean inhibitor-carboxymethylcellulose affinity columns. A protease-BEPCI complex has been isolated by ion exchange chromatography. A dual physiological function of inhibition and protection of the seed protease is suggested as a plausible role of seed protease inhibitors.
mesh_terms: D002846:Chromatography, Affinity; D002918:Chymotrypsin; D008970:Molecular Weight; D010447:Peptide Hydrolases / Q000302:isolation & purification; D010940:Plant Proteins / Q000302:isolation & purification*; D011480:Protease Inhibitors; D012639:Seeds / Q000378:metabolism*; D014357:Trypsin; D014361:Trypsin Inhibitors / Q000302:isolation & purification
chemical_list: D010940:Plant Proteins; D011480:Protease Inhibitors; D014361:Trypsin Inhibitors; D010447:Peptide Hydrolases; D002918:Chymotrypsin; D014357:Trypsin