Isolation and characterization of a trypsin inhibitor from lima beans

Abstract

1. 1. The purification of a lima bean protein fraction of high trypsin-inhibiting activity is described. The active protein was freed from inert crystallizable protein. 2. 2. The inhibitor shows remarkably high sulfur (5.5%) and cystine (16%) contents. Preliminary amino acid analyses are presented. 3. 3. The inhibitor is relatively resistant to denaturing conditions. It is not attacked by pepsin or papain. 4. 4. The average molecular weight of the concentrate was approximately 10,000 by osmotic pressure and ultracentrifugal analysis. 5. 5. The inhibitor is not inactivated by extensive esterification of its carboxyl groups, or by iodination and coupling of its phenolic and imidazole groups. Blocking of part of the amino and amide or guanidyl groups, sulfation of the hydroxyl groups, or extensive reduction of the disulfide bonds destroys its activity. 6. 6. Marked differences exist between the properties and essentiality of groups of the lima bean inhibitor and those of ovomucoid and the soybean inhibitor.