L-myo-inosose-1 as a probable intermediate in the reaction catalyzed by myo-inositol oxygenase.
L-myo-inosose-1 as a probable intermediate in the reaction catalyzed by myo-inositol oxygenase.
复制标题
L-myo-inosose-1 可能是肌醇加氧酶催化反应中的中间体。
DOI：
10.1021/bi00370a065
复制
发表时间：
1986
期刊：
影响因子：
2.9
通讯作者：
Hamilton,GA
中科院分区：
文献类型：
--
作者：
Naber,NI;Swan,JS;Hamilton,GA
Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802 Received April 8, 1986; Revised Manuscript Received June 24, 1986 abstract: In previous investigations, it was necessary to have Fe (II) and cysteine present in order to assay the catalytic activity of purified hog kidney myo-inositol oxygenase. In the present study it was found that, if this purified nonheme iron enzyme is slowly frozen in solution with glutathione and stored at-20 C, it is fully active in the absence of activators if catalase is present to remove adventitious H202. With this simpler assay system it was possible to clarify the effects of several variables on the enzymic reaction. Thus, the maximum velocity is pH-dependent with a maximum around pH 9.5, but the apparent Km for myo-inositol (air atmosphere) remains constant at 5.0 mM throughout a broad pH range. The enzyme is quite specific for its substrate myo-inositol, is very sensitive to oxidants and reductants, but is not affected by a variety of complexing agents, nucleotides, sulfhydryl reagents, etc. In other experiments it was found that l-myo-inosose-1, a potential intermediate in the enzymic reaction, is a potent competitive inhibitor (K,= 62 µ), while other inososes and a solution thought to contain D-glucodialdehyde, another potential intermediate, are weak inhibitors. Also, both a kinetic deuterium isotope effect (kH/kD= 2.1) and a tritium isotope effect (kH/kj=7.5) are observed for the enzymic reaction when [1-2H]-and [1-3H]-myo-inositol are used as reactants. These latter results are considered strong evidence that the oxygenase reaction proceeds by a pathway involving L-myo-inosose-1 as an intermediate rather than by an alternative pathway that would have D-glucodialdehyde as the intermediate. The other evidence suggests that the catalytically active form of the enzyme is a reduced species that can be reversibly converted to a catalytically inactive oxidized form but that higher valence states of the iron are probably involved during catalytic turnover, especially in the alcohol to ketone step.
