The effect of oxygen on riboflavin phosphate-dependent photosynthetic phosphorylation by spinach chloroplasts.

The process of photosynthetic phosphorylation by spinach chloroplasts has been under active investigation since it was discovered by Arnon et aZ. (2). There has been some apparent confusion about the effect of oxygen on this process. Thus Arnon et al. (2) first reported that oxygen was necessary for photophosphorylation, but then concluded in a later paper that “in the presence of the proper combination of cofactors, photosynthetic phosphorylation was found to proceed much more rapidly anaerobically than aerobically” (3). Wessels (4, 5), on the other hand, reported consistent effects of oxygen on the behavior pattern of photophosphorylation with various cofactors, and suggested a functional role for oxygen (5). Krall et al. (6) used 018 to demonstrate that photophosphorylation with riboflavin phosphate and menadione as cofactors involved neither evolution nor consumption of oxygen, but Jagendorf and Avron (7) also noted that photophosphorylation with suboptimal amounts of cofactor was stimulated by oxygen. Further, Krogmann (8, 9) described an oxygen-dependent photophosphorylation with trichlorophenol indophenol. This process, termed oxidative photophosphorylation, appeared to be completely dependent on oxygen, unlike the photophosphorylation with other cofactors such as riboflavin phosphate, menadione, and N-methyl phenaaonium sulfate which act both anaerobically and aerobically. The present studies were undertaken with the hope of clarifying the role of oxygen in the photophosphorylation process. The experiments described here were carried out primarily with photophosphorylation elicited by the cofactor FMN.1 The effect of oxygen with this cofactor was studied in detail and compared with the oxygen effects on the indophenol photophosphorylation system. Evidence will be presented that oxygen affects these two systems in quite different ways.