Tryptic fragments of phaseolin from protein isolates of Phaseolus beans

Crystalline and amorphous protein isolates from white kidney and navy beans (Phaseolus vulgaris) and baby lima and large lima beans (Phaseolus lunatus) were subjected to tryptic hydrolysis. The hydrolysis was monitored by the nitrogen solubility index (NSI) and reverse phase-high performance liquid chromatography/mass spectrometry (RP-HPLC/MS) analysis of the hydrolysates. The results of the NSI and RP-HPLC showed that the tryptic fragments of the crystalline isolates possessed higher solubility properties than the fragments of the amorphous isolates. The results of the MS study of phaseolin peptides in the RP-HPLC fractions of the hydrolysates showed that trypsin-specific bonds located in β-structured regions of β-phaseolin are resistant to tryptic hydrolysis, and that the most susceptible bonds to trypsin hydrolysis are located in regions not directly involved in the formation of secondary structural units, but in regions of disordered structure, or in regions interconnecting secondary structural units. Some trypsin-specific bonds located within α-helical structures were also cleaved by trypsin hydrolysis.