PHOSPHATIDYLSERINE EXPOSURE AND AMINOPHOSPHOLIPID TRANSLOCASE ACTIVITY IN RH-DEFICIENT ERYTHROCYTES

Endogenous phosphatidylserine (PS) exposure and lipid transport activi ty have been investigated for seven unrelated cases of Rh-null erythro cytes. Endogenous PS exposure was measured by prothrombinase activity. Out of six cases studied, two Rh-null samples exhibited abnormal amin ophospholipid exposure, as suggested by the measurement of a lower Km of factor Xa for prothrombin, Aminophospholipid translocase activity w as measured through the transbilayer redistribution of spin-labelled a nalogues of phospholipids. Provided that incubation conditions allow t he maintainance of intracellular ATP level, no difference was observed between Rh,,ll and control erythrocytes, clearly indicating that the aminophospholipid translocase and Ph polypeptides are different molecu lar species.