Electron Transport in Bacillus popilliae

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Abstract
Bacillus popilliae was found to be unique among aerobic micro-organisms in that it was deficient in a hydrogen-peroxide-scavenging system. Neither catalase nor peroxidase was found. At the same time, a system for producing hydrogen-peroxide during oxidation of reduced nicotinamide-adenine-dinucleotide (NADH2) was consistently present in the soluble fraction of extracts of cells from older cultures. Cells harvested from 9-hr. cultures did not produce a significant amount of peroxide. The soluble NADH2 oxidase was apparently a flavoprotein, since it was stimulated by flavin-nucleotides, insensitive to cyanide and azide, and inhibited by Atabrine. Also, difference spectra demonstrated the presence of a reducible flavin in the soluble fraction of cell extracts. The particulate fraction of cell extracts was shown by difference spectra to contain cytochrome-b1; the strong inhibition of NADH2 oxidation by cyanide, azide, and carbon-monox-ide indicated that a terminal cytochrome oxidase was also present. This system was also flavin-dependent, since it was strongly inhibited by Atabrine. The specific activity of the NADH2 oxidase in the particulate fraction was lower in extracts of cells from older cultures than in those from exponentially growing cultures. Cytochromec was not found in extracts of these cells. It is believed that the increased participation of the hydrogen-peroxide-generating NADH2 oxidase in cells of older cultures may be responsible for the rapid loss in cell viability noted in stationary-phase cultures.