SEPARATION OF LIGHT AND DARK STAGES IN PHOTOPHOSPHORYLATION

Abstract

Use of a rapid injection technique has made possible the separate study of light and dark events in photophosphorylation. It has been shown that ADP, phosphate, and Mg, and a pH of 8. 0 are requirements in the dark stage. The redox cofactor must be present in the light stage in order to have an effect. A pH of 6. 0 or below during the light stage produces much higher yields, in part by inhibiting the dark decay rate of a labile intermediate and apparently in part by an increase in the total amount of intermediate that can be produced in the light. Maximal yields were 1 mole of ATP formed/15 moles of spinach chlorophyll present. Evidence is presented that the intermediate is neither a purely photochem ical entity, nor a high energy phosphate compound, nor an activated form of the redox cofactor. Its possible identity is discussed.