Sulphotransferase and its substrate: adenosine-3'-phosphate-5'-phosphosulphate in human fetal liver and placenta.

The activity of sulphotransferase (ST) towards 2-naphthol and the concentration of its endogenous substrate adenosine-3'-phosphate-5'-phosphosulphate (PAPS) were measured in human fetal and adult liver and in the placenta. The activity of ST (mean +/- SD; nmol/min/mg protein) was 0.28 +/- 0.06 (fetal liver); 1.82 +/- 0.44 (adult liver; p less than 0.001) and 0.021 +/- 0.014 (placenta; p less than 0.001). The concentration of PAPS (mean +/- SD; nmol/g wet tissue) was 10.1 +/- 0.9 (fetal liver); 23.4 +/- 2.4 (adult liver; p less than 0.001) and 3.6 +/- 1.1 (placenta; p less than 0.001). Both ST and PAPS were higher in fetal liver than in placenta. The difference between fetal liver and placenta was more marked for ST than for its substrate. Such a consideration was also drawn when fetal and adult liver were compared. Thus, the activity of the ST rather than the concentration of its substrate seems to be the limiting factor in sulphation.