STUDIES ON PHOTOPHOSPHORYLATION: I. TWO-STEP EXCITATION KINETICS OF PHOTOPHOSPHORYLATION

Based on the observations on the time lag and the low efficiencyof photophosphorylation at low light intensities, a ‘two-stepexcitation kinetics’ of photophosphorylation of chloroplastswas developed, which could explain some of the hitherto unexplainedfacts concerning photophosphorylation. By analyses of the experimental results along the line of thetheory, it was inferred that the assumed substance (X) responsiblefor ATP formation occurs in a relatively large quantity of about1 mole/5–20 moles of chlorophyll. It was concluded thatthe high energy intermediate (X^**) of ATP formation which wasassumed to accumulate on pre-illuminating the chloroplasts (inthe absence of ADP and Pi) does not represent a side pool ofextra energy, but a substantial intermediate in the normal courseof ATP formation. Alternative possibilities for the explanation of the experimentalfacts were also discussed. ¹This paper is submitted to the University of Tokyo to fulfilla part of the requirements for the doctorate of H. SAKURAI.