Possible mechanism of photophosphorylation in Rhodopseudomonas viridis.

ABSTRACT

Photophosphorylation in the presence of (32P) inorganic phosphate (Pi) and ADP or Pi and (beta 32P) -ADP was carried out in membranes of Rhodopseudomonas viridis. When Pi and (32P)-ADP were used, 32Pi and (32P)-ATP were detected by ion exchange chromatography and the specific activity of the (beta 32P)-ADP recovered was substantially diminished. Moreover, when the (32P)-ATP was analyzed, the radioactivity was equally distributed between its beta and gamma position. When 32Pi and ADP were used instead, most of the radioactivity was found as (32P)-ATP although consistently (beta-32P)-ADP was detected. When the (32P)-ATP was analyzed, 90% of the label was found in its gamma phosphate and the remaining in its beta position. These results cannot be explained as a direct addition of phosphate to ADP as being the sole mechanism of photophosphorylation, and we propose that this pattern of labeling may be explained by a transphosphorylation reaction between one bound and one free ADP.