[Diphenoloxidases: presence in the membrane of human erythrocyte (author's transl)].

Diphenoloxidases, enzymes which accelerate the auto-oxidation of epinephrine and Dopa, have been described by one of us in blood platelets. Earlier we identified these enzymes in different animal species and particularly in human red blood cells. With the object of localising these enzymes and of understanding their function in vivo, we separated the ghosts of red blood cells according to the method described by Fairbanks G., Steck, T.L. and Wallach, D.F.H. (1971) (Biochemistry 1, 2606) and using the protease inhibitors diisopropylfuorophosphate (DFP) (10(-3) M) and 6-aminocaproic acid 10(-2) M in sodium phosphate buffer, 5 X 10(-3) M (pH 8). These ghosts, totally free of haemoglobin, were first of all pulverised in liquid nitrogen then treated ultrasonically. The supernant shows the presence of a band of diphenoloxidase activity on starch gel electrophoresis and two bands on isoelectrofocusing in polyacrylamide gel pH 5 to pH 8 after incubation with 0.02 M Dopa, 0.076 M Tris, 0.005 M citric acid, 0.004 M magnesium, pH 8.7 for 2 h at 37 degrees C. These enzymes differ from (Na, K)-ATPase in that they are neither inhibited by DFP (10(-1) M) nor by EDTA (10(-2) M) but are inhibited by lead acetate 10(-2) M. Like (Na, K)-ATPase diphenoloxidases are present at membranes level. The role in vivo of these diphenoloxidases in ATPase activity of red blood cells is discussed.