A novel oxalosuccinate-forming enzyme involved in the reductive carboxylation of 2-oxoglutarate in Hydrogenobacter thermophilus TK-6.
We have previously demonstrated that the reductive carboxylation of 2-oxoglutarate in Hydrogenobacter thermophilus TK-6 is not simply a reversal of the oxidative decarboxylation catalysed by isocitrate dehydrogenase (ICDH). The reaction involves a novel biotin protein (carboxylating factor for ICDH-CFI) and ATP. In this study, we have analysed the ICDH/CFI system responsible for the carboxylation reaction. Sequence analysis revealed a close relationship between CFI and pyruvate carboxylase. Rather unexpectedly, the rate of ATP hydrolysis was greater than that of isocitrate formation or NADH oxidation. Furthermore, ATP hydrolysis catalysed by CFI was dependent on 2-oxoglutarate but not on ICDH, suggesting that a carboxylated product is formed in the absence of ICDH. The product, which was detectable only at low temperatures, was identified as oxalosuccinate. Thus, CFI was confirmed to be a novel enzyme that catalyses the carboxylation of 2-oxoglutarate to form oxalosuccinate, which corresponds to the first step of the reductive carboxylation from 2-oxoglutarate to isocitrate. The CFI-ICDH system may also be present in mammals, where it could play a significant role in modulating central metabolism.
Aoshima
Miho
M
Department of Biotechnology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8567, Japan. aomiho@mail.ecc.u-tokyo.ac.jp
Igarashi
Yasuo
Y
D000255:Adenosine Triphosphate / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D004798:Enzymes / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D007521:Isocitrate Dehydrogenase / Q000378:metabolism; D007523:Isocitrates / Q000378:metabolism; D007656:Ketoglutaric Acids / Q000378:metabolism*; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010802:Phylogeny; D011766:Pyruvate Carboxylase / Q000378:metabolism; D017421:Sequence Analysis
D001426:Bacterial Proteins; D004798:Enzymes; D007523:Isocitrates; D007656:Ketoglutaric Acids; D000255:Adenosine Triphosphate; C034219:isocitric acid; D007521:Isocitrate Dehydrogenase; C039355:isocitrate dehydrogenase (NADP+); D011766:Pyruvate Carboxylase