LIGHT-DEPENDENT PHOSPHORYLATION IN MITOCHONDRIA

Light-dependent phosphorylation (ATP synthesis) was studied in an illuminated suspension of rat liver mitochondria. At relatively high ADP concentrations (hundreds of mu-M), exposure to light was shown to cause a significant increase in ATP content in the absence of added oxidizable substrates. At moderate ADP concentrations (50-mu-M), this effect was observed only in the presence of ketoglutarate. Long exposure to light stimulated ATP hydrolysis. Rotenone, antimycin, sodium azide, dicyclohexylcarbodiimide, and oligomycin almost fully inhibited light-dependent phosphorylation. The 2,4-dinitrophenol-induced decrease in ATP levels synthesized in the dark was reversed in the light. Blue light (436 nm) was found to be the most effective. We propose that vibrational excitation quanta, formed during vibrational relaxation, and internal conversions of light-excited flavoproteins and cytochromes, are transferred to ATP-synthetase and eject ATP from the active center, thus shifting the equilibrium towards ATP accumulation.