AbstractKinetics and mechanism of proteolysis of broad bean (Vicia fabaL.) legumin by trypsin in concentrated solutions at different enzyme‐substrate ratios (E/S= 1/40, 1/100, 1/200, 1/1000) were studied. By the method of HPLC it was established that during proteolysis process (E/S= 1/40) take place both protein content decrease in hydrolysate and change of its molecular mass (from 360 to 280 kD), which evidences for the mixed type of proteolysis, including cooperative and non‐cooperative mechanisms. Decrease ofE/Sfrom 1/40 up to 1/100–1/1000 leads not only to unproportional drop in proteolysis rate, but also to decrease of the relative contribution of cooperative proteolysis which is, possibly, connected with presence in protein molecule of at least two groups of attack sites, differentiating by their affinity with enzyme. Change of enzyme‐substrate ratio is accompanied also by change of subunit composition of product of non‐cooperative proteolysis (‘modified protein’) and also of temperature and enthalpy of its