title: Transient inhibition by ribose 5-phosphate of photosynthetic O2 evolution in a reconstituted chloroplast system.
abstract: Photosynthetic oxygen evolution by a reconstituted chloroplast system utilising sn-phospho-3-glycerol (3-phosphoglycerate) ceases upon the addition of ribose 5-phosphate even though the presence of this metabolite permits a rapid and immediate CO2 fixation. The period of cessation is appreciable at 0.1 mM ribose 5-phosphate. It is lengthened as the amount of added ribose 5-phosphate is increased and by the addition of dithiothreitol, a known activator of ribulose-5-phosphate kinase. Ribulose 1,5-bisphosphate is without effect. A similar interruption of O2 evolution may also be brought about by the addition of ADP or by ADP-generating systems such as glucose plus hexokinase. Spectrophotometric experiments indicate that the reoxidation of NADPH in the presence of sn-phospho-3-glycerol is similarly affected. The transient inhibition by ribose 5-phosphate is not observed in the presence of an active ATP-generating system or in the presence of sufficient DL-glyceraldehyde to inhibit ribulose-5-phosphate kinase activity. It is concluded that ribose 5-phosphate inhibits photosynthetic O2 evolution by adversely affecting the steady-state ATP/ADP ratio and consequently the reduction of sn-phospho-3-glycerol to glyceraldehyde 3-phosphate. The results are discussed in their relation to ADP regulation of photosynthetic carbon assimilation and metabolite transport.
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D004229:Dithiothreitol / Q000494:pharmacology; D005994:Glycerophosphates / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D010428:Pentosephosphates / Q000494:pharmacology*; D010788:Photosynthesis / Q000187:drug effects*; D010944:Plants; D012266:Ribose / Q000494:pharmacology*
chemical_list: D005994:Glycerophosphates; D010428:Pentosephosphates; D002245:Carbon Dioxide; D012266:Ribose; D010100:Oxygen; D004229:Dithiothreitol