Chen K, Wu H F, Grimsby J, Shih J C
Department of Molecular Pharmacology and Toxicology, School of Pharmacy, University of Southern California, Los Angeles 90033.
Mol Pharmacol. 1994 Dec;46(6):1226-33.
A trout liver monoamine oxidase (MAO) cDNA was cloned by screening a cDNA library with a human MAO-A cDNA probe. The trout MAO cDNA encodes 499 amino acids, with a molecular mass of 56.6 kDa. The deduced amino acid sequence of trout MAO shows 70% and 71% identity with those of human MAO-A and MAO-B, respectively. Trout MAO contains the pentapeptide sequence Ser-Gly-Gly-Cys-Tyr, to which the cofactor FAD is covalently bound. Transient expression of the cDNA in COS-7 cells shows that trout MAO oxidizes both serotonin [5-hydroxytryptamine (5-HT)] and beta-phenylethylamine (PEA), unlike human MAO-A and MAO-B, which oxidize only 5-HT and PEA, respectively. The Km for 5-HT is similar for trout MAO (130 +/- 17 mM) and human MAO-A (68 +/- 4 mM). The Km for PEA is similar for trout MAO (12.5 +/- 2.0 mM) and human MAO-B (1.5 +/- 0.2 mM). When 5-HT is used as a substrate, trout MAO is more sensitive to clorgyline (IC50, 2.8 +/- 0.2 x 10(-8) M) than deprenyl (IC50, 1.0 +/- 0.1 x 10(-6) M), a result similar to the inhibition selectivity of human MAO-A. However, trout MAO is less sensitive to clorgyline than is human MAO-A (IC50, 5.8 +/- 0.1 x 10(-10) M). Trout MAO is less sensitive to deprenyl (IC50, 4.6 +/- 0.3 x 10(-7) M) than is human MAO-B (IC50, 1.4 +/- 0.1 x 10(-9) M) when PEA is used as the substrate. These results indicate that trout MAO displays substrate and inhibitor selectivities that are not identical to those of either MAO-A and -B, and it therefore represents a novel type of MAO. The structure of trout MAO will provide insights into the substrate and inhibitor selectivities of the MAOs.
通过用人单胺氧化酶A（MAO - A）cDNA探针筛选cDNA文库，克隆了虹鳟鱼肝单胺氧化酶（MAO）的cDNA。虹鳟鱼MAO cDNA编码499个氨基酸，分子量为56.6 kDa。推导的虹鳟鱼MAO氨基酸序列与人类MAO - A和MAO - B的氨基酸序列分别具有70%和71%的同一性。虹鳟鱼MAO含有五肽序列Ser - Gly - Gly - Cys - Tyr，辅因子黄素腺嘌呤二核苷酸（FAD）与之共价结合。该cDNA在COS - 7细胞中的瞬时表达表明，与人类MAO - A和MAO - B分别仅氧化5 - 羟色胺[5 - 羟色胺（5 - HT）]和β - 苯乙胺（PEA）不同，虹鳟鱼MAO能氧化5 - HT和PEA。虹鳟鱼MAO对5 - HT的米氏常数（Km）（130±17 mM）与人类MAO - A（68±4 mM）相似。虹鳟鱼MAO对PEA的Km（12.5±2.0 mM）与人类MAO - B（1.5±0.2 mM）相似。当以5 - HT为底物时，虹鳟鱼MAO对氯吉兰（IC50，2.8±0.2×10⁻⁸ M）的敏感性高于司来吉兰（IC50，1.0±0.1×10⁻⁶ M），这一结果与人类MAO - A的抑制选择性相似。然而，虹鳟鱼MAO对氯吉兰的敏感性低于人类MAO - A（IC50，5.8±0.1×10⁻¹⁰ M）。当以PEA为底物时，虹鳟鱼MAO对司来吉兰（IC50，4.6±0.3×10⁻⁷ M）的敏感性低于人类MAO - B（IC50，1.4±0.1×10⁻⁹ M）。这些结果表明，虹鳟鱼MAO表现出与MAO - A和 - B不同的底物和抑制剂选择性，因此它代表了一种新型的MAO。虹鳟鱼MAO的结构将为深入了解MAO的底物和抑制剂选择性提供线索。
