Light-inducible Cytochrome Reduction in Membrane Preparations from Corn Coleoptiles

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Abstract
Conditions for obtaining reproducible light-induced reduction of a b-type cytochrome in membrane fractions from coleoptiles of dark-grown Z. mays L. ''WF9 .times. Bear 38'' include a glucose-glucose oxidase system that lowers O2 tension and generates H2O2, substrate amounts of ethylenediaminetetraacetic acid which, in some manner, facilitates photoreduction by both added flavin and the endogenous photoreceptor and a sample temperature below 10.degree. C. Cytochrome reduction could be obtained by photoexcitation of either a tightly bound endogenous receptor, which is probably a flavin, or added riboflavine, FMN or FAD. The latter flavin was the least effective. The endogenous photoreceptor appears to be rather firmly bound to the membranes, suggesting that this association may also exist in vivo. When any of the above 4 photoreceptors or methylene blue were used to sensitize the reaction, a cytochrome with a reduced .alpha.-band near 560 nm and a Soret difference peak near 429 nm was the electron acceptor. This cytochrome could be clearly distinguished spectrally from other cytochromes that predominated in the membrane preparations.