The Effect of Ultraviolet Light on Mitochondria

Inactivation of mitochondrial ATPase by ultraviolet light

The present work describes experiments that show that far-ultraviolet irradiation induce the inhibition of ATPase activity in both membrane-bound and soluble F1. It was also found that ultraviolet light promotes the release of tightly bound adenine nucleotides from F1-ATPase. Experiments carried out with submitochondrial particles indicate that succinate partially protects against these effects of ultraviolet light. Titration of sulfhydryl groups in both irradiated submitochondrial particles and soluble F1-ATPase indicates that a conformational change induced by photochemical modifications of amino acid residues appears involved in the inactivation of the enzyme. Finally, experiments are described which show that the tyrosine residue located in the active site of F1-ATPase is modified by ultraviolet irradiation.

Two mechanisms of near-ultraviolet lethality in Saccharomyces cerevisiae: A respiratory capacity-dependent and an irreversible inactivation

Near-ultraviolet irradiation of actively growing yeast cells leads to cell death by two distinct mechanisms. The first type of cell death is evident after low doses of near-ultraviolet light (3 times 10-4 ergs times mm- minus 2) and is due to a reversible inactivation of the respiratory capacity of the cell. In studies with yeast mitochondrial membranes the quinones were identified as the site of inactivation by determining the relative levels of the following oxidase activities after irradiation: exogenous NADH, endogenous NADH (via isocitrate dehydrogenase), succinate, and D-lactate oxidases. A second type of cell death is caused after high doses (1.8 times 10-5 ergs times mm- minus 2) and is irreversible. The mechanism of this inactivation is unknown.

THE EFFECT OF RIBOFLAVIN DEFICIENCY AND GALACTOFLAVIN FEEDING ON OXIDATIVE PHOSPHORYLATION AND RELATED REACTIONS IN RAT LIVER MITOCHONDRIA

The effect of riboflavin deficiency and feeding of galactoflavin on the flavin content of liver mitochondria, oxidative phosphorylation, Pi–ATP exchange, and ATPase activity was studied. Both dietary riboflavin deprivation and galactoflavin feeding resulted in a depressed flavin content of mitochondria, the latter treatment resulting in a more severe flavin loss. P/O ratios under all treatments were normal as were Pi–ATP exchange rates and the oxidation of succinate. Glutamate and β-hydroxybutyrate oxidations were depressed in mitochondria from rats fed galactoflavin for 15 or 28 days. DNP-activated ATPase was elevated in both flavin-deficient and galactoflavin-fed preparations while Mg++-activated ATPase was depressed in the galactoflavin-fed preparations. These results are discussed in relation to the hypothesis that flavin is involved in energy conservation in the diaphorase region of electron transport.