The sodium cycle: A novel type of bacterial energetics |
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Authors: | V. P. Skulachev |
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Affiliation: | (1) Department of Bioenergetics, A. N. Belozersky Laboratory of Molecular Biology and Bioorganic Chemistry, Moscow State University, 119899 Moscow, USSR |
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Abstract: | The progress of bioenergetic studies on the role of Na+ in bacteria is reviewed. Experiments performed over the past decade on several bacterial species of quite different taxonomic positions show that Na+ can, under certain conditions, substitute for H+ as the coupling ion. Various primary Na+ pumps ( generators) are described, i.e., Na+-motive decarboxylases, NADH-quinone reductase, terminal oxidase, and ATPase. The formed is shown to be consumed by Na+ driven ATP-synthase, Na+ flagellar motor, numerous Na+, solute symporters, and the methanogenesis-linked reverse electron transfer system. InVibrio alginolyticus, it was found that , generated by NADH-quinone reductase, can be utilized to support all three types of membrane-linked work, i.e., chemical (ATP synthesis), osmotic (Na+, solute symports), and mechanical (rotation of the flagellum). InPropionigenum modestum, circulation of Na+ proved to be the only mechanism of energy coupling. In other species studied, the Na+ cycle seems to coexist with the H+ cycle. For instance, inV. alginolyticus the initial and terminal steps of the respiratory chain are Na+ - and H+-motive, respectively, whereas ATP hydrolysis is competent in the uphill transfer of Na+ as well as of H+. In the alkalo- and halotolerantBacillus FTU, there are H+ - and Na+-motive terminal oxidases. Sometimes, the Na+-translocating enzyme strongly differs from its H+-translocating homolog. So, the Na+-motive and H+-motive NADH-quinone reductases are composed of different subunits and prosthetic groups. The H+-motive and Na+-motive terminal oxidases differ in that the former is ofaa3-type and sensitive to micromolar cyanide whereas the latter is of another type and sensitive to millimolar cyanide. At the same time, both Na+ and H+ can be translocated by one and the sameP. modestum ATPase which is of the F0F1-type and sensitive to DCCD. The sodium cycle, i.e., a system composed of primary generator(s) and consumer(s), is already described in many species of marine aerobic and anaerobic eubacteria and archaebacteria belonging to the following genera:Vibrio, Bacillus, Alcaligenes, Alteromonas, Salmonella, Klebsiella, Propionigenum, Clostridium, Veilonella, Acidaminococcus, Streptococcus, Peptococcus, Exiguobacterium, Fusobacterium, Methanobacterium, Methanococcus, Methanosarcin, etc. Thus, the sodium world seems to occupy a rather extensive area in the biosphere. |
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Keywords: | Na+ cycle Na+-NADH-quinone reductase Na+-motive oxidase Na+-ATP-synthase Na+ motor H+ cycle |
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