Cloning of a novel monoamine oxidase cDNA from trout liver.
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.
Chen
K
K
Department of Molecular Pharmacology and Toxicology, School of Pharmacy, University of Southern California, Los Angeles 90033.
Wu
H F
HF
Grimsby
J
J
Shih
J C
JC
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D003001:Cloning, Molecular; D018076:DNA, Complementary; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008969:Molecular Sequence Data; D008995:Monoamine Oxidase / Q000235:genetics*; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid; D014337:Trout
D018076:DNA, Complementary; D008996:Monoamine Oxidase Inhibitors; D008995:Monoamine Oxidase