Abnormal red cell membrane phosphatase activity in an unidentified congenital hemolytic anemia

The erythrocyte membrane contains a neutral phosphatase, which was studied with p-nitrophenyl-phosphate as the substrate. The enzyme was investigated in four members of the same family, suffering from a congenital spherocytic hemolytic anemia. Although the condition was transmitted as a dominant trait, it was not identified to the common hereditary spherocytosis. The phosphatase, instead of having a Michaelis-Menten kinetics, displayed a dramatically biphasic kinetics: substrate excess generated partial inhibition of the enzyme. We consider that such an abnormality, which was never encountered before, is a distinctive feature of a given type of congenital hemolytic anemia.