Conversion of the chemical energy of methylmalonyl-CoA decarboxylation into a Na⁺gradient

Abstract

Primary active transport systems establish electrochemical gradients of their transport substrates at the direct expense of chemical or light energy. The chemical energy can be provided by cleavage of the phosphoric anhydride bond of ATP, establishing Na⁺, K⁺, H⁺ or Ca²⁺ gradients with the respective ATPases. Whereas in eukaryotic cells the Na⁺ and K⁺ imbalance between cells and the surrounding fluids is brought about by the (Na⁺ + K⁺)ATPase¹, no such enzyme is known for bacterial cells. Generally, the gradients of Na⁺ and K⁺ ions in these cells are believed to be generated by secondary transport systems consuming the energy provided by the electrochemical gradient of protons^2,3. In some bacterial species, however, sodium ions may be transported by primary ATP or light-driven sodium pumps^4,5. The primary sodium pump oxaloacetate decarboxylase represents a novel energy conversion mechanism in that it consumes the chemical energy of the decarboxylation of oxaloacetate to drive Na⁺ transport^6–8. We show here that methylmalonyl-CoA decarboxylase is another example of a Na⁺ transport enzyme converting the chemical energy of a decarboxylation reaction into an ion gradient.