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  • Title: Regulation of rat pineal hydroxyindole-O-methyltransferase: evidence of S-adenosylmethionine-mediated glucocorticoid control.
    Author: Sandrock AW, Leblanc GG, Wong DL, Ciaranello RD.
    Journal: J Neurochem; 1980 Sep; 35(3):536-43. PubMed ID: 7452273.
    Abstract:
    Rat pineal hydroxyindole-O-methyltransferase is controlled similarly to adrenal medullary phenylethanolamine N-methyltransferase. S-adenosylmethionine (SAM), the in vivo cofactor utilized by the enzyme to convert N-acetylserotonin to melatonin, protects this methyltransferase against tryptic proteolysis in vitro. Furthermore, in vivo studies suggest that the nucleoside itself is controlled by glucocorticoids. Hypophysectomy decreases hydroxyindole-O-methyltransferase levels as compared with control animals, while dexamethasone and SAM administration restore enzyme levels toward control values. In vitro proteolytic studies further demonstrate that, although N-acetylserotonin does not stabilize the enzyme against trypsinization, this substrate acts synergistically with SAM to confer greater stabilization than observed with SAM alone.
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