Biological and biochemical properties of crystalline and amorphous proteins from Phaseolus beans

摘要

Bipyramidal crystalline, spheroidal crystalline and amorphous proteins were prepared from following four seeds: white kidney, navy (Phaseolus vulgaris) beans; baby lima, large lima (Phaseolus lunatus) beans. A study of the biological properties of the proteins which exhibit the different microstructures, was carried out. The nature of tryptic inhibitory activity and alpha-amylase inhibitory activity were investigated. All protein showed both trypsin inhibitory and alpha-amylase activities; the kinetics of the alpha-amylase revealed non-competitive mechanism. The crystalline isolates showed lower trypsin inhibitory (TI) and alpha-amylase inhibitory (AI) activities than the amorphous isolates. The extents of tryptic hydrolysis (in vitro) were not related to TI indicating involvement of some other factors, in addition to trypsin inhibitory activity. Electropherograms of SDS-PAGE indicated that the major proteins of P. lunatus beans were more resistant to tryptic hydrolysis than the major fractions of the P. vulgaris. Phytate was found to have an effect on trypsin inhibition as well as on alpha-amylase inhibition; in the latter case, however, phytate complexed to protein was required for the inhibitory effect. There were no relationships between tannin content of the proteins and biological activity. Fractionation of bipyramidal crystalline and amorphous proteins by size exclusion chromatography showed that each isolate contained three fractions having approximate MW of 443,000, 200,000 and 150,000 daltons. The 200,000 MW fraction was a principal fraction. The fraction of 150,000 contained most of the trypsin inhibitory activity, alpha-amylase inhibitory activity was not detected in any of the fractions.