Initial Events of Light-Dependent ATP Synthesis in Spinach Subchloroplast Particles

Abstract
The kinetics of 32Pi incorporation into adenine nucleotides by subchloroplast [spinach] particles in the light is studied with a continuous flow apparatus allowing measurements between 3 and 200 ms. After a short lag time from 1-3 ms ATP synthesis proceeds with a constant rate. During the first few milliseconds a faster labeling of ADP is detected. This labeling of ADP reaches a constant level up to 1 molecule ADP labeled/molecule of coupling factor present. The labeling pattern in ATP indicates that the labeled ADP does not equilibrate with free ADP. The addition of 32Pi to a phosphorylating system during the light phase (32Pi pulse) exhibits unchanged kinetic characteristics for labeling of ATP and ADP. These results indicate phosphorylation of AMP to ADP as an intermediate step in photophosphorylation. In experiments carried out in the dark no label is found in ATP within the time analyzed. However the labeling of ADP occurs in the same way as in the light.

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