Size distribution and photophosphorylation of chromatophores from t Rhodospirillum rubrum

Morphology and photophosphorylation of chromatophores from t Rhodospirillum rubrum have been investigated by dynamic light scattering (DLS) and in situ ³¹P-NMR measurement. Two components, designated as light and heavy fractions, with different average sizes and size distributions were detected by the DLS and can be separated by sucrose density gradient centrifugation. The light fraction has an average size of about 140 nm in diameter with a narrow distribution and shows a high activity of photophosphorylation. About 70 of ADP were found to be converted to ATP purely by the photophosphorylative reaction. In contrast, the heavy fraction has a broad size distribution centered around 350 nm and a low activity of photophosphorylation. Only about 50 of ADP was converted into ATP and AMP with a ratio of 7:3, indicating that most membrane-bound adenylate kinase are attached on the particles of the heavy fraction. Effect of physical disruption on the structural integrity of chromatophores has been examined by using sonication with various oscillating strengths. The result shows that the morphology of chromatophores for both light and heavy fractions is relatively stable to the disruption, while the photophosphorylative activity of the light fraction is very sensitive to the disrupting strength, suggesting that the internal structure of the purified chromatophores could be partially damaged by the disruption.