Chromatophores are membrane-bound particles containing photosynthetic pigments in photosynthetic bacteria such as Rhodospirillum rubrum and Chromatium. Electron microscopy reveals they are flattened disk-shaped or vesicular structures ranging from 50-100 nanometers in diameter, though size varies by species. Compositionally, chromatophores are rich in protein (approximately 61%) and phospholipid (22%), along with bacteriochlorophyll, carotenoids, and complete electron transport chain components including cytochromes and coenzyme Q. These particles catalyze light-dependent photophosphorylation, converting ADP to ATP at rates up to 150 micromoles per hour per milligram of bacteriochlorophyll. Recent research demonstrates both cyclic and non-cyclic photophosphorylation mechanisms in chromatophores, similar to plant chloroplasts. Evidence suggests chromatophores form only under conditions permitting photosynthetic pigment synthesis and may originate from preformed lipoprotein matrices associated with the cytoplasmic membrane. The formation of bacteriochlorophyll appears linked to protein synthesis, with labeled amino acids incorporated into chromatophore protein at higher rates than soluble protein during pigment synthesis.

Key findings

• Chromatophores are discrete membrane-bound particles containing all photosynthetic pigments in photosynthetic bacteria, isolable by centrifugation with sedimentation constants around 190 Svedberg units
• These particles catalyze light-dependent phosphorylation of ADP to ATP (photophosphorylation) through cyclic and non-cyclic mechanisms involving electron transport chain components
• Chromatophores have similar composition to non-photosynthetic bacterial electron transport particles, consisting primarily of protein (~61%) and phospholipids (~22%), with bacteriochlorophyll and carotenoid pigments
• Formation of chromatophores appears coupled to protein synthesis and photosynthetic pigment synthesis, with the particles absent in aerobically grown cells lacking pigments
• Chromatophores contain subunits or 'subchromatophores' that are functionally complete and can be released by sonic oscillation