Photophosphorylation in Presence and Absence of Added Adenosine Diphosphate in Chromatophores from Rhodospirillum rubrum.

Abstract

Photophosphorylation in chromatophores from R. rubum has been studied in the presence of a limiting (bound) and an excess (added) amount of adenosine diphosphate (ADP). The following results have been obtained. The chromatophores possessed a small but definite capacity for esterification of P32 i in light. It could be detected by using a p32 i solution of very high specific activity. The product thus formed was rapidly dephosphorylated in the dark. In the presence of an appropriate concentration of ascorbate the amount of product once formed in light with an excess amount of Pi was nearly unchanged under continuous illumination. This amount was, however, reduced even under continuous illumination if ascorbate was added in too high concentration, which introduced dephosphorylation of the product formed. Addition of ferricyanide increased the rate of decomposition of product once formed in light was added Pi. Based on these finding, the mechanism of energy transfer coupled with photo-synthetic electron transport in R. rubrum is discussed.