Chromatium cytochrome

Abstract

A cytochrome preparation was obtained from the photoautotrophic bacterium Chromatium sp. strain D, an obligate anaerobe, by sonic oscillation of acetone powders of the cells. The pigment, purified by ammonium sulfate fractionation and electrophoresis, had the following properties: 1. 1. The spectroscopic absorption maxima of the reduced form were at 552, 525 and 418 mμ; for the oxidized form, at 406 mμ. 2. 2. Preparation of cyanide and pyridine hemochromogens and of the free porphyrin by removal of the prosthetic group with silver salts indicated it to be of the mesoporphyrin type. 3. 3. The purified preparation had an iron content of 0.12% and an iron-heme ratio of 2.0 to 2.7. 4. 4. The E′ 0 determined by titration against the ferri-ferro oxalate system was approximately −0.040 volt at pH 7.0. 5. 5. The molecular weight determined from sedimentation and diffusion data was approximately 35,000. 6. 6. At pH 6.0, the cytochrome had an anodic mobility of 5.9·10 −5 cm 2 volt −1 second −1. At pH 7.7, the pigment separated into two colored components with different absorption spectra and electrophoretic mobilities. 7. 7. The pigment complex was stable only in the pH range 6 to 8 and was appreciably auto-oxidizable. The significance of these findings for possible heterogeneity of cellular hemoproteins and for electron transport in Chromatium is discussed.