Transfer of high-energy phosphate in bovine rod outer segments. A nucleotide buffer system.

The nucleotide requirement for the recycling of NADPH, necessary in rod outer segment cytoplasm for the reduction of the chromophore upon bleaching, has been investigated. It is found that the latter process specifically requires ATP. Using this specificity the pathways have been investigated, by which in the rod outer segment cytoplasm ATP is resynthesized from other high-energy phosphate donors. It is found that enzyme activities are present, which can rapidly reshuffle the high-energy phosphate groups between the various adenine and guanine nucleotides as well as from creatine phosphate. These phosphate transfers may occur so rapidly that light-induced changes in nucleotide concentrations could easily be a delusive criterion for the enzymatic process underlying these changes.