Human brain sulphotransferase and glucuronyltransferase

The activities of cytosolic sulphotransferase (ST) and microsomal glucuronyltransferase (GT) were measured with 1-naphthol as the substrate in three frontal cortex, three temporal cortex, one parietal cortex, one occipital cortex and two cerebellar cortex specimens from human brain. The average activity was 11.7 +/- 4.2 pmol/min/mg protein/(ST) and 26.8 +/- 13.6 pmol/min/mg protein (GT). The kinetics of ST were studied varying the concentration of 1-naphthol in five brain specimens (temporal cortex, temporal subcortex, occipital cortex, cerebellum cortex and frontal cortex) whereas those of GT were studied in a sample obtained by pooling the microsomal fractions from the following eight brain tissues: one frontal cortex, four temporal cortex, one parietal cortex and two cerebellar cortex specimens. The Km of the first and second enzyme was 1.55 +/- 0.47 microM (mean +/- s.d.) and 121 microM, respectively. The Vmax values were 13.70 +/- 8.16 (mean +/- s.d.) pmol/min/mg protein (ST) and 103 pmol/min/mg protein (GT). Vmax/Km was ten times higher for ST than GT. These data suggest that ST is the predominant pathway at low concentrations of 1-naphthol whereas at higher concentrations, GT becomes the predominant pathway.