THE THRESHOLD MECHANISM OF THE CASCADE PR OTEOLYSIS CONTROL

The immune lysis rate of erythrocytes vs. the concentration of particu lar complement components was studied. It was found that in the presen ce of component C1 (but not C3) and factors B and D, the cells undergo lysis after the concentration of these compounds exceeds a ''threshol d'' value. The threshold molar concentrations of factors D and B excee ded 5- and 20-fold, respectively, that of component C1. The multiplici ty and different capacities of the thresholds allow the fragmentary ac tivation of cascade proteolysis at stretches between neighboring thres holds without the total realization of the final effect of the system (cell lysis, clot formation, etc.). The resulting peptideby-products ( bypass peptides) may possess their own biological activity. It is the generation of various bioregulators that appears to be the main functi on of;the cascade proteolytic systems functioning in the subthreshold regime.