Respiratory Chain of an Obligate Alkalophilic Bacillus YN-1
Akira HIGASHIBATA*a, Taketomo FUJIWARAa, and Yoshihiro FUKUMORIb
a Department of Life Science, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama 226, Japan
b Deapartment of Biology, Kanazawa University, Kakuma-machi, Kanazawa 920-11, Japan
ATP synthesis in the alkalophilic Bacillus alcalophilus is driven by the proton motive force that is generated by the respiratory system, just as in neutrophiles (1). However, the cytoplasm of alkalophilic bacterial cells is usually maintained at an almost neutral pH by the effect of Na+/H+-antiporter, which catalyzes the electrogenic exchange of extracellular protons for intracellular sodium ions (2,3). Therefore, a simple chemiosmotical mechanism cannot explain the ability of these alkalophilic bacteria to generate a proton motive force across the cytoplasmic membrane sufficient to synthesize ATP in the presence of a low outside proton gradient. In the present study, to ascertain the mechanism of the ATP synthesis in alkalophiles, we have investigated the respiratory system of an obligate alkalophilic Bacillus YN-1 which grows optimally at about pH 10 and found that the bacterium has cyanide-sensitive terminal and a novel cyanide-insensitive terminal in aerobic respiratory chain. The cyanide-sensitive pathway was terminated with caa3-type cytochrome c oxidase and occupied only 10% of total oxygen uptakes. On the other hand, the main cyanide insensitive pathway terminates with the non-proteinous component. The EI mass spectrum of the component showed mass signal of the fragments at the positions corresponding to the m/z values of 662. No signal was observed at the large m/z region from 800 to 1000. Furthermore the absorption spectrum was completely different from those of menaquinones reported previously. Furthermore, the cyanide- insensitive oxygen-reducing activity of the non-proteinous component was inhibited by catalase, suggesting that the product of the cyanide-insensitive pathway may be H202, not H20. Based on these results, we propose a novel biological oxygen- reduction system of an obligate alkalophilic Bacillus YN-1 which diverges at complex III and terminates with two elementary reactions. First the non-proteinous component catalyzes 2-electron reduction of oxygen to produce H202. Secondly, the toxic product is diminished by the effect of catalase. This combination of two reactions appears to generate water molecules as a final product of respiration in this system.
1. Guffanti, A.A., Bornstain, R.F., and Krulwich, T.A. (1981) Oxidativephosphorylation by membrane vesicles from Bacillus alcalophilus, Biochim. Biophys. Acta, 635, 619-630.
2. Krulwich, T.A., and Guffanti, A.A. (1989) Alkalophilic Bacteria., Annu. Rev. Microbiol., 43, 435-463.
3. Krulwich, T.A., and Guffanti, A.A. (1989) The Na+ cycle of extreme alkalophiles, a secondary Na+/H+ antiporter and Na+/solute symporters., J. Bioenerg. Biomembr., 21,663-677.
