Adali O, Carver G C, Philpot R M
Department of Biology, Middle East Technical University, Ankara, Turkey.
Exp Toxicol Pathol. 1999 Jul;51(4-5):271-6. doi: 10.1016/S0940-2993(99)80004-9.
This study was carried out to investigate the molecular basis for modulation of recombinant FMO3-catalyzed activity by the tricyclic antidepressants, imipramine and chlorpromazine. A mutant of human liver FMO3 (T428R) was formed by site-directed mutagenesis and characterized along with the native enzyme in order to elucidate a possible structure-function relationship. Functional properties of native and T428R human FMO3s were studied with methimazole as substrate. Both enzymes catalyzed the S-oxidation of methimazole with the same Km value. Imipramine modulated the activities of the native and T428R human FMO3s differently; the activity of the native FMO3 was increased at all concentrations, whereas the activity of the mutant enzyme was inhibited at concentrations above 300 microM. Chlorpromazine activated the native enzyme at all concentrations of methimazole but activated the mutant enzyme only at high substrate concentrations. The direction (activation or inhibition) and extend of modulation of FMO3 activity is not only dependent on the concentration of the modulator, it is also dependent on the substrate concentration. This study confirms our previous findings with FMO1 that position 428 is important in the interaction of the FMO with modulators.
本研究旨在探究三环类抗抑郁药丙咪嗪和氯丙嗪对重组FMO3催化活性进行调节的分子基础。通过定点诱变构建了人肝脏FMO3的一个突变体（T428R），并将其与天然酶一起进行表征，以阐明可能的结构-功能关系。以甲巯咪唑为底物研究了天然和T428R人FMO3的功能特性。两种酶催化甲巯咪唑的S-氧化反应时具有相同的Km值。丙咪嗪对天然和T428R人FMO3活性的调节方式不同；在所有浓度下天然FMO3的活性均升高，而突变酶在浓度高于300 microM时活性受到抑制。氯丙嗪在所有甲巯咪唑浓度下均激活天然酶，但仅在高底物浓度下激活突变酶。FMO3活性调节的方向（激活或抑制）和程度不仅取决于调节剂的浓度，还取决于底物浓度。本研究证实了我们之前对FMO1的研究结果，即428位在FMO与调节剂的相互作用中很重要。
