Studies on photosynthetic processes. I. The effect of light intensity on triphosphopyridine nucleotide reduction, adenosine triphosphate formation, and carbon dioxide assimilation in spinach chloroplasts.

Although there is a considerable amount of information on the effect of light intensity on O2 evolution and, to a lesser extent, COz assimilation in intact plants (l), there are few reports on the effect of light intensity on the photosynthetic processes known to occur in the isolated chloroplast and chloroplast fragments. Isolated chloroplasts have the ability to assimilate CO2 (‘2, 3), and chloroplast fragments reduce triphosphopyridine nucleotide and generate adenosine triphosphate from adenosine diphosphate and inorganic orthophosphate when illuminated (4). Jagendorf and Avron (5) have presented data on the rates of phosphorylation (using phenazine methosulfate or flavin mononucleotide) and the Hill reaction (with trichlorophenol indophenol) as functions of light intensity. Krogmann (6) investigated the effect of light intensity on oxidative photophosphorylation by spinach chloroplasts using trichlorophenol indophenol as acceptor. The reduction of diphosphopyridine nucleotide by chromatophores from Rhodospirillum rubrum in various light intensities has also been studied (7). There is, however, no report of the effect of light intensity on adenosine triphosphate formation with triphosphopyridine nucleotide as electron acceptor or on the process of triphosphopyridine nucleotide reduction. Similarly, there is no information on the effect of light intensity on CO2 fixation by chloroplasts. In the present investigation, the effect of light intensity on CO2 fixation by the isolated intact chloroplast and on reduced triphosphopyridine nucleotide and adenosine triphosphate formation by chloroplast fragments were studied.