MOLECULAR-CLONING, EXPRESSION, AND CHARACTERIZATION OF A NOVEL MOUSE-LIVER SULT1B1 SULFOTRANSFERASE

A mouse liver homogenate was shown to contain enzymatic activities cat alyzing the sulfation of 3,4-dihydroxyphenylalanine (Dopa) and tyrosin e isomers with a pH optimum of 8.25, Western blot analysis revealed a 34 kDa protein exhibiting immunologic crossreactivity to antiserum aga inst rat liver SULT1B1 sulfotransferase. By employing the reverse tran scriptase-polymerase chain reaction (RT-PCR) technique, a 910-base pai r product encoding the putative mouse liver SULT1B1 sulfotransferase w as obtained. Using this PCR product as a probe, a cDNA containing the entire open reading frame of the mouse liver SULT1B1 sulfotransferase was cloned from a mouse liver Lambda ZAP cDNA library. The nucleotide sequence indicated it is a new enzyme. The deduced amino acid sequence exhibited 87,6, 72.3, 55.9, 54.2, 52.8, 51.1, and 49.4% identity to t he amino acid sequences of the rat liver SULT1B1 sulfotransferase, hum an thyroid hormone sulfotransferase, mouse phenol sulfotransferase, ra t liver phenol sulfotransferase, rat liver hydroxyarylamine sulfotrans ferase, mouse estrogen sulfotransferase, and rat estrogen sulfotransfe rase. Upon transfection of COS-7 cells with an expression vector (pcDN A3) harboring the cDNA encoding this new enzyme, a 34 kDa protein exhi biting immunologic cross-reactivity to antiserum against the rat liver SULT1B1 sulfotransferase was expressed. The recombinant sulfotransfer ase exhibited enzymatic activities toward Dopa and tyrosine isomers, a s well as dopamine and 3,3',5-triiodo-L-thyronine. Northern blot analy ses indicated the SULT1B1 sulfotransferase was predominantly expressed in liver, but not in the other ten mouse organs examined. Furthermore , the enzyme was found to be expressed in a developmental stage-depend ent manner, being at a very low level in liver samples from 1-day-old mice and then gradually increasing to the maximum level in liver sampl es from 4-week-old mice.