Evidence for a role of tyrosyl residues in cell membrane permeability.

In the presence of tyrosinase, red blood cells are Ipsed. Lysis follows an enzyme-mediated reaction, with the amount of lysis being proportional to the tyrosinase concentration. Cyanide, which inhibits tyrosinase, prevents lysis of the red blood cells by tyrosinase. Heat-denatured tyrosinase has no effect on red blood cells. Tyrosinase also exhibits a pronounced effect on the permeability of isolated rat diaphragms. Glucose uptake is inhibited 28 to 44 % whereas glycine uptake is stimulated 50% by tyrosinase. Ehrlich ascites cells, in the presence of tyrosinase, show decreased viability as measured by eosin dye uptake. These data strongly suggest that the tyrosyl residues of the protein layers of the cell membrane are involved in the maintenance of cell membrane integrity.