Mast cells in the thymus of NZB mice

Pepper, Rollin E. (Michigan State University, East Lansing), and Ralph N. Costilow. Electron transport in Bacillus popilliae . J. Bacteriol. 89: 271–276. 1965.— Bacillus popilliae was found to be unique among aerobic microorganisms 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 (NADH 2 ) 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 NADH 2 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 b 1 ; the strong inhibition of NADH 2 oxidation by cyanide, azide, and carbon monoxide 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 NADH 2 oxidase in the particulate fraction was lower in extracts of cells from older cultures than in those from exponentially growing cultures. Cytochrome c was not found in extracts of these cells. It is believed that the increased participation of the hydrogen peroxide-generating NADH 2 oxidase in cells of older cultures may be responsible for the rapid loss in cell viability noted in stationary-phase cultures.