THE PHOTOCHEMICAL OXIDATION OF DPNH WITH RIBOFLAVIN PHOSPHATE

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Abstract
When a solution of reduced diphosphopyridine nucleotide (DPNH) plus riboflavin phosphate was illuminated aerobically, the DPNH rapidly decreased and disappeared. The level of DPNH was not decreased in the dark or in the absence of the flavin. Treatment of the light-exposed mixture with dithionite regenerated the DPNH quantitatively and further illumination lead again to oxidation of the DPNH, suggesting the major change in the DPNH molecule is a loss of 2 electrons. Other procedures demonstrated that the riboflavin phosphate is the electron acceptor in the photooxidation of the DPNH and that DPNH is the predominant if not the sole source of electrons in the system. "Black light" illumination of a buffered mixture of DPNH and pyruvate leads to rapid oxidation of the coenzyme. The rate of reaction with a-ketoglutarate is lower than with pyruvate suggesting structural specificity. The authors propose that these experiments provide a model system for demonstrating how the interplay of light and a reduced coenzyme can lead to the transfer of electrons either in the "substrate direction" or toward other oxidants, molecular oxygen included.

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