Yoshida Ken-ichi, Yamaguchi Masanori, Morinaga Tetsuro, Kinehara Masaki, Ikeuchi Maya, Ashida Hitoshi, Fujita Yasutaro
Department of Agrobioscience, Graduate School of Agricultural Science, Kobe University Kobe 657-8501, Japan.
J Biol Chem. 2008 Apr 18;283(16):10415-24. doi: 10.1074/jbc.M708043200. Epub 2008 Feb 28.
The iolABCDEFGHIJ operon of Bacillus subtilis is responsible for myo-inositol catabolism involving multiple and stepwise reactions. Previous studies demonstrated that IolG and IolE are the enzymes for the first and second reactions, namely dehydrogenation of myo-inositol to give 2-keto-myo-inositol and the subsequent dehydration to 3D-(3,5/4)-trihydroxycyclohexane-1,2-dione. In the present studies the third reaction was shown to be the hydrolysis of 3D-(3,5/4)-trihydroxycyclohexane-1,2-dione catalyzed by IolD to yield 5-deoxy-d-glucuronic acid. The fourth reaction was the isomerization of 5-deoxy-D-glucuronic acid by IolB to produce 2-deoxy-5-keto-D-gluconic acid. Next, in the fifth reaction 2-deoxy-5-keto-D-gluconic acid was phosphorylated by IolC kinase to yield 2-deoxy-5-keto-D-gluconic acid 6-phosphate. IolR is known as the repressor controlling transcription of the iol operon. In this reaction 2-deoxy-5-keto-D-gluconic acid 6-phosphate appeared to be the intermediate acting as inducer by antagonizing DNA binding of IolR. Finally, IolJ turned out to be the specific aldolase for the sixth reaction, the cleavage of 2-deoxy-5-keto-D-gluconic acid 6-phosphate into dihydroxyacetone phosphate and malonic semialdehyde. The former is a known glycolytic intermediate, and the latter was previously shown to be converted to acetyl-CoA and CO(2) by a reaction catalyzed by IolA. The net result of the inositol catabolic pathway in B. subtilis is, thus, the conversion of myo-inositol to an equimolar mixture of dihydroxyacetone phosphate, acetyl-CoA, and CO(2).
枯草芽孢杆菌的iolABCDEFGHIJ操纵子负责肌醇的分解代谢，该过程涉及多个逐步反应。先前的研究表明，IolG和IolE是第一步和第二步反应的酶，即肌醇脱氢生成2-酮基-肌醇，随后脱水生成3D-(3,5/4)-三羟基环己烷-1,2-二酮。在本研究中，第三步反应被证明是由IolD催化的3D-(3,5/4)-三羟基环己烷-1,2-二酮水解生成5-脱氧-D-葡萄糖醛酸。第四步反应是由IolB催化的5-脱氧-D-葡萄糖醛酸异构化生成2-脱氧-5-酮-D-葡萄糖酸。接下来，在第五步反应中，2-脱氧-5-酮-D-葡萄糖酸被IolC激酶磷酸化生成2-脱氧-5-酮-D-葡萄糖酸6-磷酸。IolR是已知的控制iol操纵子转录的阻遏物。在该反应中，2-脱氧-5-酮-D-葡萄糖酸6-磷酸似乎是通过拮抗IolR与DNA的结合而作为诱导剂的中间体。最后，IolJ被证明是第六步反应的特异性醛缩酶，将2-脱氧-5-酮-D-葡萄糖酸6-磷酸裂解为磷酸二羟丙酮和丙二酸半醛。前者是已知的糖酵解中间体，后者先前已被证明可通过IolA催化的反应转化为乙酰辅酶A和CO₂。因此，枯草芽孢杆菌中肌醇分解代谢途径的最终结果是将肌醇转化为磷酸二羟丙酮、乙酰辅酶A和CO₂的等摩尔混合物。
