Expression and activities of sulfotransferase in rat brain

Sulfotransferase (SULT) has been found in the brain; however, the details of its function remain unclear. The present study aimed to elucidate the regional differences in the expression of SULT1 and SULT2 mRNA and SULT activities in the eight functional regions of the rat brain (cerebellum, cortex, hippocampus, medulla oblongata, midbrain, olfactory bulb, striatum, and thalamus). All SULT1 isoforms were detected in the medulla oblongata and thalamus. SULT2A1 mRNA was not observed in any of the eight regions, whereas SULT2B1a and SULT2B1b were found in all regions. The SULT2B1b mRNA expression level in the medulla oblongata was 1.7-fold higher than that in the liver. The sulfonation of p-nitrophenol and pregnenolone was detected in all regions. The kinetics of p-nitrophenol sulfonation in the cerebellum fitted to the substrate inhibition model (K_m = 37.6 nM, V_max = 2.72 pmol/min/mg, V_inh = 1.60 pmol/min/mg, and K_i = 0.87 μM). The pregnenolone sulfonation also exhibited substrate inhibition kinetics (K_m = 0.99 μM, V_max = 1.53 pmol/min/mg, and K_i = 54.67 μM). We clarified that SULT1 and SULT2 were expressed and had metabolizing capacities in the rat brain, suggesting that brain SULTs may be involved in metabolism of endogenous compounds and drugs.