Sodium ion-translocating decarboxylases.
The review is concerned with three Na(+)-dependent biotin-containing decarboxylases, which catalyse the substitution of CO(2) by H(+) with retention of configuration (DeltaG degrees '=-30 kJ/mol): oxaloacetate decarboxylase from enterobacteria, methylmalonyl-CoA decarboxylase from Veillonella parvula and Propiogenium modestum, and glutaconyl-CoA decarboxylase from Acidaminococcus fermentans. The enzymes represent complexes of four functional domains or subunits, a carboxytransferase, a mobile alanine- and proline-rich biotin carrier, a 9-11 membrane-spanning helix-containing Na(+)-dependent carboxybiotin decarboxylase and a membrane anchor. In the first catalytic step the carboxyl group of the substrate is converted to a kinetically activated carboxylate in N-carboxybiotin. After swing-over to the decarboxylase, an electrochemical Na(+) gradient is generated; the free energy of the decarboxylation is used to translocate 1-2 Na(+) from the inside to the outside, whereas the proton comes from the outside. At high [Na(+)], however, the decarboxylases appear to catalyse a mere Na(+)/Na(+) exchange. This finding has implications for the life of P. modestum in sea water, which relies on the synthesis of ATP via Delta(mu)Na(+) generated by decarboxylation. In many sequenced genomes from Bacteria and Archaea homologues of the carboxybiotin decarboxylase from A. fermentans with up to 80% sequence identity have been detected.
Buckel
W
W
Laboratorium für Mikrobiologie, Fachbereich Biologie, Philipps-Universität, D-35032, Marburg, Germany. buckel@mailer.uni-marburg.de
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism; D002262:Carboxy-Lyases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002414:Cations, Monovalent; D003653:Decarboxylation; D004734:Energy Metabolism; D043586:Methylmalonyl-CoA Decarboxylase; D008956:Models, Chemical; D011522:Protons; D012964:Sodium / Q000737:chemistry / Q000378:metabolism*
D001426:Bacterial Proteins; D002414:Cations, Monovalent; D011522:Protons; C024582:N1'-carboxybiotin; D001710:Biotin; D012964:Sodium; D002262:Carboxy-Lyases; C023060:glutaconyl CoA decarboxylase; C021916:oxaloacetate decarboxylase; D043586:Methylmalonyl-CoA Decarboxylase