To investigate the mechanism of phytohemagglutinin (PHA) susceptibility or resistance to the action of proteolytic enzymes, its in vitro proteolysis by trypsin was studied. It was found that Ca (2+) gives resistance to the native PHA molecule to trypsin proteolysis. In the absence of Ca (2+) trypsin performs a thorough hydrolysis of PHA. At the first stage of trypsin hydrolysis of PHA the formation of a relatively stable high molecular mass product occurs (PHA-T) as a result of non-co-operative proteolysis. At the second stage, the degradation of PHA-T occurs, and this degradation is performed by parallel co-operative proteolysis. This type of proteolysis differs from the action of trypsin on phaseolin, the main storage protein from common bean ( Phaseolus vulgaris L.). The implications of Ca (2+)influence of PHA hydrolysis by trypsin are discussed.

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