title: Ribulose diphosphate carboxylase/oxygenase. IV. Regulation by phosphate esters.
abstract: The stimulation or inhibition of ribulose diphosphate oxygenase by a variety of compounds is compared with the reported effects on these compounds on the ribulose diphosphate carboxylase activity. A possible transition state analog of ribulose diphosphate, 2-carboxyribitol 1, 5-diphosphate, at a molar ratio of inhibitor to enzyme of 10 to 1, irreversibly inactivates the oxygenase and carboxylase activities. This is consistent with the hypothesis that there may be a single active site for both the carboxylase and oxygenase activities. Several compounds of the reductive pentose photosynthetic carbon cycle act as effectors of the ribulose diphosphate oxygenase in a manner complementary to their reported effect upon the carboxylase. Ribose 5-phosphate inhibits the oxygenase with an apparent Ki of 1.8 mM, but it is reported to activate the carboxylase; fructose 6-phosphate and glucose 6-phosphate act similarly but are less effective than ribose 5-phosphate. Fructose 1. 6-diphosphate stimulates the oxygenase at low magnesium ion concentrations. The stimulatory effect of 6-phosphogluconate on the oxygenase is associated with a 3-fold reduction of the Km (Mg2+). ATP inhibits the oxygenase but has been reported to stimulate the carboxylase; pyrophosphate acts in an opposite manner. From these results it appears that the ratio of carboxylase to oxygenase activity may be a variable factor with predictable subsequent alteration in the ratio between photosynthetic CO2 fixation and photorespiration.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D002262:Carboxy-Lyases / Q000378:metabolism*; D011756:Diphosphates / Q000494:pharmacology; D005636:Fructosephosphates / Q000494:pharmacology; D005958:Glucosephosphates / Q000494:pharmacology; D006598:Hexosediphosphates / Q000494:pharmacology; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D009943:Organophosphorus Compounds / Q000494:pharmacology*; D010101:Oxygen Consumption; D010105:Oxygenases / Q000378:metabolism*; D010429:Pentoses / Q000494:pharmacology; D010944:Plants / Q000201:enzymology; D012267:Ribosemonophosphates / Q000494:pharmacology; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D012274:Ribulosephosphates; D013402:Sugar Alcohols / Q000494:pharmacology
chemical_list: D011756:Diphosphates; D005636:Fructosephosphates; D005958:Glucosephosphates; D006598:Hexosediphosphates; D009943:Organophosphorus Compounds; D010429:Pentoses; D012267:Ribosemonophosphates; D012274:Ribulosephosphates; D013402:Sugar Alcohols; D000255:Adenosine Triphosphate; D010105:Oxygenases; D002262:Carboxy-Lyases; D012273:Ribulose-Bisphosphate Carboxylase; D008274:Magnesium