Phenotypic variation in the phosphotransferase activity of human red cell acid phosphatase (ACP1)

Red cell acid phosphatase (ACP1) catalyses the transfer of phosphate from phosphate ester substrates to suitable acceptor alcohols such as methanol and glycerol. The rate of substrate turnover in the presence of acceptors is increased by the increment of the phosphotransferase reaction, thus allowing this activity to be measured. There is specificity with regard to acceptors: (a) polyols (e.g., glycerol) are better acceptors than the corresponding n-alcohols, and (b) polyol configuration and chain length determine acceptor activity. Ribitol was the most efficient acceptor found. Each of the three common ACP1 alleles is represented electrophoretically by two isozyme bands; the phosphotransferase activity of the anodal isozyme was found to be more than twice that of the cathodal isozyme. The extent of phosphotransferase activity is also genotype dependent. In the presence of 2 M glycerol, the relative phosphotransferase efficiencies for the three homozygote types were: ACP1 B = 3.7, ACP1 A = 3.4, and ACP1 C = 2.5. This pattern of B greater than A greater than C is the same as found for the modulation of ACP1 by purines and folates.