Glutaconate CoA-transferase from Acidaminococcus fermentans.

1. Glutaconate CoA-transferase catalyses the transfer of CoAS- from acetyl-CoA preferentially to (E)-glutaconate, but glutarate, (R)-2-hydroxyglutarate, acrylate and propionate are also good acceptors. No reaction was observed with (Z)-glutaconate and C4-dicarboxylic acids. 2. The product of the reaction of acetyl-CoA with (E)-glutaconate is the 1-isomer of glutaconyl-CoA, i.e. the thiol ester is conjugated with the double bond. Other results indicate, however, that with (R)-2-hydroxyglutarate as substrate both possible isomers are generated. 3. Glutaconate CoA-transferase was purified from cell-free extracts of Acidaminococcus fermentans to apparent homogeneity and crystallized. The relative molecular mass of the enzyme is approximately 275000. It consists of two different polypeptide chains (M, 32000 and 34000). On the catalytic pathway a thiolester is formed between CoASH and a carboxylate of the smaller polypeptide chain. 4. The structural and functional relationships between glutaconate CoA-transferase and other CoA-transferases are discussed. 5. Glutaconate CoA-transferase is also present in other bacteria fermenting glutamate via hydroxyglutarate. Experiments with an antiserum against the enzyme indicate that the transferase is necessary for the decarboxylation of glutaconate but not for the dehydration of (R)-2-hydroxyglutarate.