Effects of metabolite binding to ribulosebisphosphate carboxylase on the activity of the Calvin photosynthesis cycle

Abstract

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. 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. 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.

Evidence for a methylammonium-binding site on methylamine dehydrogenase of Thiobacillus versutus

“…A similar binding site for monovalent cations (Cs', NH4+, and Naf) has been identified in the crystal structure of bovine liver rhodanese, where the cation is coordinated to four peptide carbonyl oxygens and an aspartate side chain carboxylate (Kooystra et al, 1988). It should be kept in mind, however, that the MADH X-ray structure was obtained at pH 5.0 and that at low pH the substrate-and cation-affinity of MADH is very low (Kuusk & McIntire, 1994;Gorren & Duine, 1994).…”

Identification of a potential metal cation–π binding site in the structure of a thermophilicBacillus stearothermophilustriosephosphate isomerase mutant

“…The distance between the ion and the indole ring (4.1±4.3 A Ê ) is compatible with earlier reports (Wouters, 1998), although it is longer than the mean distance observed in smallmolecule structures (cation centroid of the aromatic distance around 3.4 A Ê ). De®nite con®rmation of the presence of a metal cation±% binding site could be obtained by replacing the Na + ion by an Rb + ion (Di Cera et al, 1995) or a Cs + ion (Kooystra et al, 1988) cation.…”

“…The interaction between a sodium cation and a tryptophan residue has also recently been identi®ed in a 2 A Ê crystallographic structure of hen egg-white lysozyme (Wouters, 1998). A more conclusive example is from rhodanese, where Trp287 is in close contact with a Cs + ion (Kooystra et al, 1988).…”

Experimental Evidence for Alkali Metal Cation−π Interactions

“…The coordination of a Cs ϩ cation by aromatic residues has been documented in three protein crystal structures: rhodanese, [58] glutamine synthetase, [59] and methylamine dehydrogenase. [60] The role of this binding site in rhodanese is unclear.…”