Membrane-protease interactions. III: A consideration of the difference in binding potential of pancreatic proteases to erythrocytes and erythrocyte ghosts.

Trypsin and chymotrypsin readily bind to human erythrocyte ghosts and to resealed right-side-out ghosts, but not to intact erythrocytes, as followed with [3H]trypsin and [3H]chymotrypsin and with cold proteases in a caseinolytic assay. The proteases freely reacted with casein in the presence of intact cells. Trypsin activated trypsinogen over an 8-hr time course at a faster rate in the presence of erythrocytes than in the absence thereof, after a slight initial delay. Trypsinogen did not bind to intact erythrocytes, thereby behaving comparably to trypsin. These results suggest that different microenvironments exist about the erythrocyte ghosts and the intact erythrocytes, thereby permitting the proteases to bind to the former but not to the latter. Hence, in the absence of considerable ghosts in circulating blood, which may mask the binding site of the proteases, the proteases may be more readily accessible for interaction with circulating serpins, leading to inactivation of the proteases and protection from their degradative potential. The presence of the serpins in circulating blood may assist in the control of the degradative power of the pancreatic proteases in pancreatitis and may negatively modulate such processes as thrombosis, activation of the complement system, and vascular remodeling.