Human platelet phenol sulfotransferase: stability of two forms of the enzyme with time and presence of a racial difference

Thermolabile (TL) and thermostable (TS) forms of human platelet phenol sulfotransferase (PST) were measured over various periods of time. TL PST was assayed with dopamine as the substrate and TS PST was measured with phenol and with p-nitrophenol. Levels of TL and TS PST from the same subjects did not change significantly over 1 day, 1 week, 4 weeks, and 8.5 months. Interassay coefficients of variation of PST activities over 3-4 weeks measured in samples from 8-12 subjects with dopamine, phenol and p-nitrophenol were 13.96%, 13.60% and 13.30%, respectively. There was a significant correlation between PST activity measured in the same samples with phenol and with p-nitrophenol (r = 0.946, n = 18, p <0.0001). TS PST activity measured with p-nitrophenol was significantly higher (p <0.0001) in platelets from 51 black subjects than the level of TS PST in samples from 52 white subjects (0.72 ± 0.06 vs 0.42 ± 0.04 units/10⁸ platelets, respectively; mean ± SEM). These results demonstrate the 'stability' of the levels of both forms of the enzyme with time. They also point out the usefulness of a reproducible assay for the detection of a racial difference in the levels of TS PST.