Enzymatic properties, tissue-specific expression, and lysosomal location of two highly homologous rat SULT1C2 sulfotransferases

We have isolated two highly homologous but distinct rat sulfotransferase cD NAs termed ratSULT1C2 and ratSULT1C2A encoding polypeptides of 297 amino ac ids each. The amino acid sequence of ratSULT1C2 is 84% identical to the hum an SULT1C2 and 81% identical to a rabbit SULT1C2 sulfotransferase. ratSULT1 C2 and ratSULT1C2A are 92% identical but differ in 22 amino acids. The majo rity of these amino acid substitutions in ratSULT1C2A is not found in the h uman and rabbit SULT1C2, which identifies ratSULT1C2 as the orthologue of t hese sulfotransferases, whereas SULT1C2A is a closely related but distinct enzyme, ratSULT1C2 and 2A sulfotransferases do not sulfonate steroids, dopa mine, acetaminophen, or cy-naphthol, but only p-nitrophenol. Prokaryoticall y expressed ratSULT1C2A is less active than ratSULT1C2. ratSULT1C2/2A mRNAs are abundant in kidney and less abundant in stomach and liver. The enzymes are expressed as 34-kDa polypeptides in rat kidney, liver, and stomach. In addition, a 28-kDa cross-reacting polypeptide is found in kidney only. Imm unohistochemistry revealed expression of ratSULT1C2/2A in the epithelial ce lls of the proximal tubules of the kidney, bile duct epithelia, hepatocytes , and the epithelium of the gastric mucosal glands. Although the cDNA predi cted amino acid sequence identifies both sulfotransferases as cytosolic enz ymes, in tissue sections, in the kidney cell line NRK 52, and in transientl y transfected BHK cells a considerable fraction of the enzyme was found in a granular perinuclear compartment. Costaining with a lysosomal marker in g astric mucosa tissue sections and cultured cells identifies these structure s as lysosomes. (C) 2000 Academic Press.