ANALYSIS OF GENE MUTATION IN THAI CAUSING FISH ODOR SYNDROME

我们检测了三甲胺（TMA）在人肝微粒体中的代谢。TMA n -氧化动力学参数的表观Km和Vmax值分别为45.9 μM和2.24 nmol/min/mg蛋白。已知的含黄素单加氧酶（FMO）抑制剂如甲巯咪唑和热处理均能抑制TMA的n-氧化，但细胞色素P450抑制剂SKF-525A不能抑制TMA的n-氧化。为了确定对TMA进行n氧化的FMO形式，测定了大肠杆菌中表达的人FMO1、FMO3和FMO5的TMA n氧化酶活性。FMO5无TMA n氧化酶活性。考察TMA n -氧化动力学参数时，FMO3的Vmax/Km值约为FMO1的355倍。我们分析了泰国可能的鱼臭综合征患者的FMO3基因。在2例患者的外显子3中发现了一种新的突变，即在265位（G265A）上从G到A的单碱基替换。突变的FMO3蛋白在58号残基上由缬氨酸替换为异亮氨酸（V58I），在沙门氏菌中表达时，TMA n氧化酶活性降低。我们得出结论，该突变的FMO3基因产生了催化活性降低的FMO蛋白。

We examined the metabolism of trimethylamine (TMA) in human liver microsomes. The kinetic parameters of TMA N-oxidation showed the apparent Km and Vmax values of 45.9 μM and 2.24 nmol/min/mg protein, respectively. The N-oxidation of TMA was inhibited by the known flavin-containing monooxygenase (FMO) inhibitors such as methimazole and heat treatment, but not by SKF-525A, cytochrome P450 inhibitor. To identify the FMO form responsible for the N-oxidation of TMA, the TMA N-oxidase activities of human FMO1, FMO3 and FMO5 expressed in E, coli were measured. FMO5 showed no TMA N-oxidase activity. The Vmax/Km value for FMO3 was about 355 times higher than that for FMO1 when the kinetic parameters of TMA N-oxidation was examined. We analyzed the FMO3 gene of Thai possible patients with fish-odor syndrome. A novel mutation, a single base substitution from G to A at the position of 265 (G265A), was identified in exon 3 of two patients. The mutated FMO3 protein with an amino acid substitution from valine to isoleucine at residue 58 (V58I) exhibited the reduced TMA N-oxidase activity when it was expressed in Salmonella. We conclude that FMO3 gene with this mutation produce the FMO protein that has reduced catalytic activities.