Site of photosynthetic electron-transport systems coupling phosphorylation with chromatophores from Rhodospirillum rubrum

Abstract

• 1.

  1. With chromatophores from Rhodospirillum rubrum, phosphorylations coupled with photosynthetic electron-transport systems have been investigated.

• 2.

  2. Under illumination with white light at a fixed high intensity, the addition of a strictly limited concentration of phenazine methosulfate was required to induce photophosphorylation at a maximal rate. The maximal rate of photophosphorylation was always much faster when induced by phenazine methosulfate than when induced by the other reagents tested such as ascorbate or succinate. The ratio of maximal rate of the phenazine methosulfate-induced to ascorbate-induced photophosphorylation varied from batch to batch of chromatophore preparations with experimental values from 2 to 5.

• 3.

  3. The phenazine methosulfate-induced, and ascorbate-induced photophosphorylations were inactivated in a similar manner by illumination of chromatophores with ultraviolet irradiation and by additions of the following inhibitors: Na₂SO₄, quinacrine hydrochloride, 2,4-dinitrophenol, dicumarol EDTA and phenylmercuric acetate. Chromatophore suspensions, if resonicated or heated, lost the activity of ascorbate-induced photophosphorylation somewhat more rapidly than that of phenazine methosulfate-induced photophosphorylation. In the presence of an appropriate concentration of o-phenanthroline, the ascorbate-induced and succinate-induced photophosphorylations were inactivated completely, but the phenazine methosulfate-induced photophosphorylation was not affected. With the chromatophores treated with an appropriate concentration of Triton X-100, the ascorbate-induced and succinate-induced photophosphorylations were inactivated completely, whereas the phenazine methosulfate-induced photophosphorylation was inactivated only partially.

• 4.

  4. The photooxidations of cytochrome c₂, and cytochrome c were stimulated in rate by the addition of ADP. The stimulation by ADP was not significantly influenced in the presence or absence of P_i. The photooxidation was stimulated by 2,4-dinitrophenol in the absence but not in the presence of ADP. The concentraton of 2,4-dinitrophenol required for the stimulation was nearly identical with that required for the inhibition of photophosphorylation.

• 5.

  5. ATP was synthesized from ADP and P_i, coupled with the photooxidations of cytochrome c₂, and cytochrome c. The values of the P/O ratio obtained were less than one.

• 6.

  6. Based on these findings, the site for phosphorylation coupled with the photosynthetic electron-transport systems are suggested.