Effects of metabolite binding to ribulosebisphosphate carboxylase on the activity of the Calvin photosynthesis cycle.
1. The regulatory implications of the interaction of ribulosebisphosphate carboxylase with metabolites participating in the Calvin photosynthesis cycle has been examined by control analysis based on our recently described kinetic model for photosynthetic carbohydrate formation in the chloroplast of C3 plants. The results provide clear evidence that the Calvin cycle activity under conditions of light and CO2 saturation is insignificantly affected by the inhibition of ribulosebisphosphate carboxylase caused by metabolites such as 3-phosphoglycerate, fructose 1,6-bisphosphate, sedoheptulose 1,7-bisphosphate, NADPH, and inorganic orthophosphate. 2. Due to the exceptionally high stromal concentration of the carboxylase, metabolite binding to the enzyme affects the Calvin cycle activity indirectly by reducing the pool of free orthophosphate and phosphorylated metabolites available for the cyclic reactions. This pool reduction corresponds typically to about 5 mM total phosphate and derives mainly from the binding of ribulose bisphosphate and orthophosphate. 3. Substantial amounts of the metabolites interacting with ribulosebisphosphate carboxylase are present in an enzyme-bound form. The bound form of the Calvin cycle intermediates sedoheptulose bisphosphate, fructose bisphosphate, and ribulose bisphosphate typically accounts for about 70, 80, and 90%, respectively, of the total stromal concentration of the intermediate.
D050260:Carbohydrate Metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology*; D005635:Fructosediphosphates / Q000378:metabolism; D005988:Glyceric Acids / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D009249:NADP / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism / Q000494:pharmacology; D010788:Photosynthesis; D010944:Plants / Q000201:enzymology*; D012273:Ribulose-Bisphosphate Carboxylase / Q000378:metabolism*; D013403:Sugar Phosphates / Q000378:metabolism
D005635:Fructosediphosphates; D005988:Glyceric Acids; D010710:Phosphates; D013403:Sugar Phosphates; D002245:Carbon Dioxide; D009249:NADP; C022079:sedoheptulose 1,7-bisphosphate; C005156:3-phosphoglycerate; D012273:Ribulose-Bisphosphate Carboxylase; C029063:fructose-1,6-diphosphate