On the Mechanisms of Photochemical Reductions of FAD and FAD‐Dependent Flavoproteins

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Abstract
The rate for photoreduction of riboflavin 5′‐phosphate is faster than flavin‐adenine dinucleotide which can be effectively photoreduced to the hydroquinone level by: ethylenediaminetetraacetate > ethylenediaminetetrapropionate > l‐methionine > nicotine > dimethylamino‐propanol > dimethylglycine ethyl ester > triethylamine. The same compounds can be used to photoreduce flavoproteins, the rates for which are: d‐amino acid oxidase > l‐amino acid oxidase > glucose oxidase > oxynitrilase > Shethna flavoprotein. The oxidation, reduction stage achieved is characteristics of the protein.Addition of free flavin markedly enhances the photoreduction of those flavoproteins which have a readily dissociable flavin‐adenine dinucleotide. Urea enhances the photoreduction rate of flavoproteins in approximate corespondence to their ease of photoreduction in the absence of this reagent. Increase in temperature does not greatly enhance the rate of photoreduction of these flavoproteins. Benzoate decreases the rate of photoreduction of certain of the oxidases.