CHARACTERIZATION OF ESTRONE SULFATASE ACTIVITY IN HUMAN THROMBOCYTES

Estrone sulfatase is an important enzyme which catalyzes the productio n of estrone from estrone sulfate in a variety of human and animal tis sues. We report, for the first time, on the presence of estrone sulfat ase activity in thrombocytes from human blood. Incubation of [H-3]estr one sulfate in the presence of human thrombocyte lysates resulted in t he formation of [H-3]estrone as assessed by two-dimensional TLC. Estro ne sulfatase activity was localized in the mitochondrial-microsomal fr action in thrombocytes from human blood. The enzyme was thermostable a nd had an optimum pH of 5.60 in acetate buffer. The highest activity w as obtained in the presence of 0.1% of either Nonidet P-40 or Triton X -100. Phosphate ions (1 mM) inhibited the enzyme activity by 64% and s imilar effects were observed in the presence of platelet-free plasma. Endogenous inhibitors had no effect on the observed enzyme activity un der assay conditions as evidenced in this study. The apparent K(m) val ue was 3.16 +/- 0.08 muM for [H-3]estrone sulfate and V was 188.5 +/- 2.6 (mean +/- SEM, n = 22) pmol . mg protein-1.h-1. Comparison between two thrombocyte preparative procedures provided evidence that thrombo cyte estrone sulfatase activity should be measured in thrombocyte samp les representing the whole thrombocyte population. This parameter appe ared critical for accurate measurements of enzyme activity. The presen ce of estrone sulfatase activity in human thrombocytes provides a new non-invasive tool for the study of this activity both in physiological and pathological conditions which could be of potential clinical rele vance.