Photoreduction and Photooxidation of Cytochrome c by Spinach Chloroplast Preparations.

The photoreduction of cytochrome c by spinach chloroplasts has been noted by several investigators (12, 20, 25). In a preliminary report, we have presented evidence that aqueous digitonin extracts of spinach chloroplasts contain a cytochrome c photooxidase (22) which appears to be similar to the photooxidase present in extracts of photosynthetic bacteria studied by Kamen and Vernon (13, 14, 32). The present paper describes the behavior toward cytochrome c of wvhole chloroplasts prepared in hypertonic salt solution, and outlines the experiments which led to the demonstration of their cytochrome c-photooxidase activity.