THE ENZYMATIC BASIS FOR THE RAT-LIVER 6-HYDROXYMELATONIN SULFOTRANSFERASE ACTIVITY

Understanding 6-hydroxymelatonin (6HM) sulfation is deemed important t o explaining normal and oncostatic actions of the pineal gland. Here w e identify the enzymatic basis for this sulfation in rats. First, a qu antitative assay was designed for measuring hepatic 6HM sulfotransfera se (6HMST) activity. The assay was then used to identify a male domina nt sexual dimorphism wherein liver from males contains double the 6HMS T per g or per 100 g body weight seen in females. Examination of other rat tissues showed that most in vivo 6HM sulfation was likely to occu r in liver. In addition, DEAE-Sephadex chromatography of liver cytosol indicated that 80-90% of the 6HMST activity in both sexes was due to an enzyme we named 6HMST II. A minor 6HM sulfotransferase (6HMST I) el uted from the columns prior to the main enzyme. 6HMST II, purified add itionally, was shown to convert 6HM to a product that appeared to be 6 HM sulfate (6-sulfatoxymelatonin). The enzyme was inhibited by Na+, K, Zn2+, and Cd2+. Its pH optimum was 7.80 +/- 0.30. Comparisons are ma de between 6HMST II, dopamine sulfotransferase II, and aryl sulfotrans ferase IV.