Light-induced electron transport in Chromatium strain D I. Isolation and characterization of Chromatium chromatophores

Abstract

Fractionation of Chromatium Strain D chromatophores by centrifugation in sucrose density gradients results in two fractions, designated ‘light’ and ‘heavy’. The light particles are enriched in photosynthetic pigments, are relatively homogeneous and can be prepared reproducibly. They do not scatter light appreciably, contain 41% of the bacteriochlorophyll, 26% of the carotenoid, 25% of the heme and 4% of the protein found in intact cells, and are approx. 75% lipid, and 25% protein, 30% of which can be ascribed to cytochromes. The molecular weight is 12.9.10 6. In contrast, the heavy particles are heterogeneous, can not be prepared reproducibly, scatter light and contain approx. 14% of the bacteriochlorophyll, 9% of the carotenoid, 8% of the heme and 6% of the protein present in intact cells. Three meso-heme proteins were identified in the light particles: cytochrome c−552, cytochrome cc′, and cytochrome c−555. Both cytochrome c−552 and cytochrome cc′ bound CO when solubilized but not when bound in the light particles. No protoheme ( b- type cytochrome) was found, even in whole cells. These results permit characterization of the chemical and physical properties of a subcellular fraction of Chromatium Strain D, which does not appear to be an artifact of preparation.