Abstract
Procedures for the precise assay of human platelet phenol sulphotransferase activity were determined. The coefficient of variation of the assay was 5.8% when the enzyme activity was expressed per 108 platelets, and was 9.4% when it was expressed per mg soluble platelet protein. Mean platelet phenol sulphotransferase (PST) activity in samples from 102 randomly selected adults was 1.2 ± 0.4 units/108 platelets (mean ± S.D.), with a range from 0.2 to 2.9. The mean activity for umbilical cord blood platelet PST was 0.93 ± 0.3 units/108 platelets (mean ± S.D., n = 27). The substrate used routinely for the assay was 3-methoxy-4-hydroxyphenylglycol (MHPG). There was a significant correlation between the formation of MHPG sulfate by individual platelet preparations and the formation of sulfated product with each of the following substrates: tyramine (r = 0.92, n = 21); dopamine (r = 0.82, n = 16); 5-hydroxytryptamine (r = 0.94, n = 20); acetaminophen (r = 0.77, n = 17); and alphamethyldopa (r = 0.77, n = 17) (p <0.001 for each). Platelet PST activity correlated significantly with human renal cortex PST activity (r = 0.54, n = 20, p <0.02). The correlation coefficient between platelet PST activity and jejunal mucosal enzyme activity in eight patients was 0.67. These results raise the possibility that human platelet PST activity measured with MHPG as substrate might reflect the enzyme activity in other tissues and the degree of sulfate conjugation of a variety of substrates.