title: On the mechanism of sodium ion translocation by methylmalonyl-CoA decarboxylase from Veillonella alcalescens.
abstract: Veillonella alcalescens during lactate degradation developed an Na+ concentration gradient with 7-8 times higher external than internal Na+ concentrations in the logarithmic growth phase. The gradient declined to a factor of 1.9 in the late stationary phase. Methylmalonyl-CoA decarboxylase reconstituted into proteoliposomes performed an active electrogenic Na+ transport, creating delta psi of 60 mV, delta pNa+ of 50 mV, and delta mu Na+ of 110 mV. In the initial phase of the transport, the decarboxylase catalyzed the uptake of 2 Na+ ions malonyl-CoA molecule decarboxylated. During further development of the electrochemical Na+ gradient, this ratio gradually declined to zero, when decarboxylation continued without further increase of the internal Na+ concentration. The rate of malonyl-CoA decarboxylation declined initially during development of the membrane potential, but remained unchanged later on. Monensin abolished the Na+ gradient and increased the malonyl-CoA decarboxylation rate 2.8-fold. On dissipating the membrane potential with valinomycin, the internal Na+ concentration reached three times higher values than in its absence, and the decarboxylation rate increased 2.8-fold. Methylmalonyl-CoA decarboxylase catalyzed an exchange of internal and external Na+ ions in addition to net Na+ accumulation. The initial rate of Na+ influx was double that of malonyl-CoA decarboxylation. In the following, both rates decreased about twofold in parallel to values which remained constant during further development of the electrochemical Na+ gradient. Thus, Na+ influx and malonyl-CoA decarboxylation follow a stoichiometry of approximately 2:1, independent of the magnitude of the electrochemical Na+ gradient and are thus highly coupled events.
authors.affiliation: Mikrobiologisches Institut der Eidgenössischen Technischen Hochschule, ETH-Zentrum, Zürich, Switzerland.
authors.forename: W
authors.initials: W
authors.lastname: Hilpert
authors.forename: P
authors.initials: P
authors.lastname: Dimroth
mesh_terms: D002262:Carboxy-Lyases / Q000378:metabolism*; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D043586:Methylmalonyl-CoA Decarboxylase; D008954:Models, Biological; D011510:Proteolipids / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014678:Veillonella / Q000201:enzymology* / Q000254:growth & development
chemical_list: D008081:Liposomes; D011510:Proteolipids; C020485:proteoliposomes; D012964:Sodium; D002262:Carboxy-Lyases; D043586:Methylmalonyl-CoA Decarboxylase