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 Ψ of 60 mV, pNa+ of 50 mV, and 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.

Energy conservation by succinate decarboxylation in Veillonella parvula

“…It remained unclear, however, how the Na+ gradient thus established could be exploited by the bacterium. Neither Na+-dependent nor H+-dependent ATPase was detected, no matter whether biochemical (Hilpert & Dimroth, 1991) or immunological methods (Laubinger et al, 1990) were applied. Propionigenium modestum, on the other hand, has a Na+-ATPase and therefore can grow with succinate as sole energy source (Hilpert et al, 1984).…”

“…The methylmalonyl-CoA decarboxylase responsible for this decarboxylation has been isolated (Galivan & Allen, 1968) and it was shown that the chemical energy of the decarboxylation reaction is converted into a Na+ gradient across the membrane (Hilpert & Dimroth, 1982). Methylmalonyl-CoA decarboxylase of V. alcalescens (now V. parvula) was characterized (Hilpert & Dimroth, 1983) and the mechanism of the Na+ translocation was clarified (Hilpert & Dimroth, 1991). The question arose whether the energy conserved in this Na+ gradient could be exploited by this bacterium.…”

Microbial Propionic Acid Production

“…The sodium pumping pathway, found in organisms such as Propionigenium modestum, couples the decarboxylation of methylmalonyl-CoA derived from succinate to propionyl-CoA with the pumping of two sodium ions across the cell membrane [46]. The mechanism of this reaction is likely to be identical to the well-studied oxaloacetate decarboxylase [47] and is probably linked to the consumption of a periplasmic proton [48], leading to a net energy gain of roughly 0.25 ATP.…”

Expression of the sodium ion pump methylmalonyl-coenzyme A-decarboxylase from Veillonella parvula and of mutated enzyme specimens in Escherichia coli

“…Analysis of the purified enzyme from V. parvula allowed us to ascribe specific functions to three of these subunits. The ␣, ␤, and ␥ subunits were characterized as carboxyltransferase, carboxybiotin carrier protein decarboxylase, and biotin carrier protein, respectively (15). The functions of the ␦ subunit and of the recently detected ε subunit are not known.…”