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Articles

Light-inducible Cytochrome Reduction in Membrane Preparations from Corn Coleoptiles

I. STABILIZATION AND SPECTRAL CHARACTERIZATION OF THE REACTION ¹

Roland J. Caubergs²

Winslow R. Briggs

Kline Biology Tower, Yale University, New Haven, Connecticut 06520, Department of Biology, University of Antwerpen, Belgium, Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305

Conditions for obtaining reproducible light-induced reduction of a b-type cytochrome in membrane fractions from coleoptiles of dark-grown Zea mays L. 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 C. Cytochrome reduction could be obtained by photoexcitation of either a tightly bound endogenous receptor, which is probably a flavin, or added riboflavin, flavin mononucleotide, or flavin adenine dinucleotide. 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 four photoreceptors or methylene blue were used to sensitize the reaction, a cytochrome with a reduced -band near 560 nanometers and a Soret difference peak near 429 nanometers was the electron acceptor. This cytochrome could be clearly distinguished spectrally from other cytochromes that predominated in the membrane preparations.

¹ This research was supported in part by Grants PCM 73-D1089 and PCM 78-10198 from the National Science Foundation (to M. H. M. G.). This is Carnegie Institution of Washington—Department of Plant Biology Publication 662.

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