A novel pathway for L-citramalate synthesis in Rhodospirillum rubrum.
When [14C]propionate was incubated with a cell-free extract of Rhodospirillum rubrum in the presence of glyoxylate, ATP, CoA, Mg2+, and Mn2+, radioactivity was incorporated into mesaconate (MSA) as well as into beta-methylmalate (MMA) and citramalate (CMA). MSA was suggested to be an intermediate of the conversion of MMA to CMA based on the following observations. (i) When non-labeled MSA was added to the CMA-forming reaction system, radioactivity was trapped in MSA. (ii) When MSA was incubated with the cell-free extract, CMA was formed. (iii) The alpha-carboxyl group of CMA was shown to be derived from the beta-carboxyl group of MMA, implying that CMA was formed from MMA via MSA through successive dehydration and hydration. From the results of Sephadex G-10 column chromatography of the reaction products, beta-methylmalyl-CoA and mesaconyl-CoA were presumed to be involved in the reaction. A new CMA-forming metabolic pathway is proposed as follows: erythro-beta-methylamalyl-CoA leads to mesaconyl-CoA leads to MSA leads to L-CMA.
D006038:Glyoxylates / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D008293:Malates / Q000096:biosynthesis*; D008345:Manganese / Q000494:pharmacology; D011422:Propionates / Q000378:metabolism; D012247:Rhodospirillum rubrum / Q000378:metabolism*
D006038:Glyoxylates; D008293:Malates; D011422:Propionates; D008345:Manganese; C011729:citramalate; D008274:Magnesium