Kinetics and Properties of Cytochrome c Photooxidase of Spinach.

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Abstract
A study of the properties of the cytochrome c photooxidase system of spinach was made. The response of this system to light intensity and to wave length was observed. The relative effectiveness of light of different wave lengths indicated that the effective light was most probably absorbed by the chlorophyll of the pigmented component (Factor 1). From rate measurements at different temperatures, an experimental activation energy was calculated of 4.3 kcal/mole. The stimulation of the photooxidase by ammonium sulfate and potassium phosphate was examined in some detail. Maximum stimulation was as much as 10-fold in 1.3 to 1.5 [image] (NH4)2SO4 in the presence of 0.3 mM KCN. Part of this stimulatory effect was due to the cyanide. Phosphate and citrate also stimulated strongly, and salts of monovalent anions had smaller effects. Many typical inhibitors of photosynthesis have been shown to be without effect on cytochrome c photooxidase. The only effective inhibitors found were HgCl2, p-chloromercuribenzoate, and phenylmercuric nitrate. A survey of the distribution of the photooxidase in nature has shown that all chlorophyll-containing tissues examined contain both of the components (i.e., Factor 1 and Factor 2) of the photooxidase, and that these 2 factors interact to give an active photooxidase, regardless of the source from which they are prepared. The soluble component, Factor 2, has been shown to occur primarily in tissues containing chlorophyll.