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Changes in Adenine Nucleotides of Intact Chromatium D Produced by Illumination

^a Johnson Foundation for Medical Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104

ABSTRACT

The total adenine nucleotide content of suspensions of Chromatium D averaged 14 nmoles/mg of dry weight. Of this, one-third to one-half was adenosine triphosphate (ATP), even in suspensions incubated in darkness. Illumination with high intensities caused a rise in ATP and a drop mainly in adenosine diphosphate, the new steady state being reached in 5 to 15 sec at room temperature. The dark steady state was re-established 15 to 30 sec after returning the suspensions to darkness. The rates of these changes were little affected by the presence of electron donors or CO₂, though their magnitude was reduced when substrates were added to starved suspensions. At limiting light intensities, complex kinetics characterized the transition from both dark to light and light to dark, and, at lower light intensities, more ATP was produced in suspensions supplemented with electron donors than in starved cells. The results show that photophosphorylation accompanying cyclic electron flow occurred in intact cells, and suggest that noncyclic phosphorylation can also occur.

¹ Present address: Division of Biological Sciences, Microbiology Section, Cornell University, Ithaca, N.Y.

² Present address: Department of Biophysics and Biochemistry, Faculty of Science, University of Tokyo, Tokyo, Japan.