ON THE NATURE OF RAT HEPATIC AND MOUSE OLFACTORY SULFOTRANSFERASES

Rat hydroxysteroid sulfotransferase (HS-SULT) cDNAs, ST-40 and ST-20 a re 90% identical in amino acid sequences and show different substrate specificities toward dehydroepiandrosterone (DHEA), androsterone (AD) and cortisol (CS). ST-40 enzyme is active toward the three substrates, whereas ST-20 enzyme is preferentially active for CS, First we prepar ed mutants of well conserved histidine. lysine and asparagine by site- directed mutagenesis. Secondly we constructed 20 chimeric HS-SULTs by reciprocal exchange of five protein domains between ST-20 and ST-40 en zymes. The studies on the expressed mutant and chimeric enzymes indica te the importance of the C-terminal region for the substrate specifici ty and the involvement of multiple regions for the enzyme activities. Next we determined the genetic loci of ST-40 and ST-20 by fluorescence in situ hybridization. Biotinylated ST-20 and ST-40 probes gave a pai r of fluorescent spots on the same region of rat chromosome 1 and the loci of these genes were localized to the same chromosomal region of 1 q21.3-->q22.1. Finally we studied mouse olfactory phenol SULT (P-SULT) . It was immunolocalized in the cytoplasm of mouse olfactory sustentac ular cells and mouse nasal cytosols show high SULT activities toward p henolic aromatic odorants. We subsequently isolated a mouse P-SULT cDN A from mouse olfactory cDNA library. It encodes 304 amino acid polypep tide and is 94% identical with rat ST1C1 in amino acid sequences. (C) 1998 Elsevier Science Ireland Ltd. All lights reserved.