Sandrock A W, Leblanc G G, Wong D L, Ciaranello R D
J Neurochem. 1980 Sep;35(3):536-43. doi: 10.1111/j.1471-4159.1980.tb03688.x.
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.
大鼠松果体羟吲哚-O-甲基转移酶的调控方式与肾上腺髓质苯乙醇胺N-甲基转移酶类似。S-腺苷甲硫氨酸（SAM）是该酶在体内用于将N-乙酰血清素转化为褪黑素的辅助因子，在体外可保护这种甲基转移酶免受胰蛋白酶的蛋白水解作用。此外，体内研究表明，核苷本身受糖皮质激素调控。与对照动物相比，垂体切除会降低羟吲哚-O-甲基转移酶的水平，而给予地塞米松和SAM可使酶水平恢复至对照值。体外蛋白水解研究进一步表明，虽然N-乙酰血清素不能使该酶对胰蛋白酶处理产生稳定作用，但这种底物与SAM协同作用，比单独使用SAM能提供更大的稳定性。
