Resistance of alpha-globulin from Sesamum indicum L. to proteases in relationship to its structure.

alpha-Globulin, the high-molecular-weight protein fraction from Sesamum indicum L., was hydrolyzed to low-molecular-weight protein and peptides by pepsin, while its resistance to hydrolysis by group-specific enzymes, trypsin or alpha-chymotrypsin, was very high. The protein showed definite structural changes after proteolysis, especially after peptic hydrolysis, as evidenced from various biophysical data. The sedimentation velocity pattern of alpha-globulin hydrolyzed by trypsin or alpha-chymotrypsin indicated reduction in the percentage of 11S component, while the pepsin-hydrolyzed sample was devoid of any 11S component, indicating the absence of a native protein molecule. The fluorescence emission spectra of the various hydrolyzed alpha-globulin showed a red shift in the fluorescence emission maximum. The red shift was maximum with alpha-globulin hydrolyzed by pepsin and minimum with the trypsin-hydrolyzed sample. The far-ultraviolet-circular dichroic measurements indicated that most of the ordered structure of alpha-globulin was absent after pepsin hydrolysis, while after trypsin and chymotrypsin hydrolysis conformational changes were less.