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A mathematical model of the Calvin photosynthesis cycle

Pettersson, Gösta LU and Ryde-Pettersson, Ulf LU (1988) In European Journal of Biochemistry 175(3). p.661-672
Abstract

A mathematical model is presented for photosynthetic carbohydrate formation in C3 plants under conditions of light and carbon dioxide saturation. The model considers reactions of the Calvin cycle with triose phosphate export and starch production as main output processes, and treats concentrations of NADPH, NAD+, CO2, and H+ as fixed parameters of the system. Using equilibrium approximations for all reaction steps close to equilibrium, steady‐state and transient‐state relationships are derived which may be used for calculation of reaction fluxes and concentrations of the 13 carbohydrate cycle intermediates, glucose 6‐phosphate, glucose 1‐phosphate, ATP, ADP, and inorganic (Ortho)phosphate.... (More)

A mathematical model is presented for photosynthetic carbohydrate formation in C3 plants under conditions of light and carbon dioxide saturation. The model considers reactions of the Calvin cycle with triose phosphate export and starch production as main output processes, and treats concentrations of NADPH, NAD+, CO2, and H+ as fixed parameters of the system. Using equilibrium approximations for all reaction steps close to equilibrium, steady‐state and transient‐state relationships are derived which may be used for calculation of reaction fluxes and concentrations of the 13 carbohydrate cycle intermediates, glucose 6‐phosphate, glucose 1‐phosphate, ATP, ADP, and inorganic (Ortho)phosphate. Predictions of the model were examined with the assumption that photosynthate export from the chloroplast occurs to a medium containing orthophosphate as the only exchangeable metabolite. The results indicate that the Calvin cycle may operate in a single dynamically stable steady state when the external concentration of orthophosphate does not exceed 1.9 mM. At higher concentrations of the external metabolite, the reaction system exhibits overload breakdown; the excessive rate of photosynthate export deprives the system of cycle intermediates such that the cycle activity progressively approaches zero. Reactant concentrations calculated for the stable steady state that may obtain are in satisfactory agreement with those observed experimentally, and the model accounts with surprising accuracy for experimentally observed effects of external orthophosphate on the steady‐state cycle activity and rate of starch production. Control analyses are reported which show that most of the non‐equilibrium enzymes in the system have a strong regulatory influence on the steady‐state level of all of the cycle intermediates. Substrate concentration control coefficients for cycle enzymes may be positive, such that an increase in activity of an enzyme may raise the steady‐state concentration of the substrate is consumes. Under optimal external conditions (0.15–0.5 mM orthophosphate), reaction flux in the Calvin cycle is controlled mainly by ATP synthetase and sedoheptulose bisphosphatase; the cycle activity approaches the maximum velocity that can be supported by the latter enzyme. At lower concentrations of external orthophosphate the cycle activity is controlled almost exclusively by the phosphate translocator. At high external orthophosphate concentrations the phosphate translocator resumes predominant control, but also other non‐equilibrium enzymes gain strong flux control with one notable exception: ribulosebisphosphate carboxylase has no significant regulatory influence on the cycle activity under conditions of light and CO2 saturation, nor does it control the concentration of any cycle intermediate other than its substrate. Copyright © 1988, Wiley Blackwell. All rights reserved

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
European Journal of Biochemistry
volume
175
issue
3
pages
12 pages
publisher
Wiley-Blackwell
external identifiers
  • scopus:0024288428
ISSN
0014-2956
DOI
10.1111/j.1432-1033.1988.tb14242.x
language
English
LU publication?
yes
id
2ee3ec8e-69e9-4250-a6cc-fb016bf097a0
date added to LUP
2017-02-04 11:25:04
date last changed
2017-07-30 05:21:04
@article{2ee3ec8e-69e9-4250-a6cc-fb016bf097a0,
  abstract     = {<p>A mathematical model is presented for photosynthetic carbohydrate formation in C<sub>3</sub> plants under conditions of light and carbon dioxide saturation. The model considers reactions of the Calvin cycle with triose phosphate export and starch production as main output processes, and treats concentrations of NADPH, NAD<sup>+</sup>, CO<sub>2</sub>, and H<sup>+</sup> as fixed parameters of the system. Using equilibrium approximations for all reaction steps close to equilibrium, steady‐state and transient‐state relationships are derived which may be used for calculation of reaction fluxes and concentrations of the 13 carbohydrate cycle intermediates, glucose 6‐phosphate, glucose 1‐phosphate, ATP, ADP, and inorganic (Ortho)phosphate. Predictions of the model were examined with the assumption that photosynthate export from the chloroplast occurs to a medium containing orthophosphate as the only exchangeable metabolite. The results indicate that the Calvin cycle may operate in a single dynamically stable steady state when the external concentration of orthophosphate does not exceed 1.9 mM. At higher concentrations of the external metabolite, the reaction system exhibits overload breakdown; the excessive rate of photosynthate export deprives the system of cycle intermediates such that the cycle activity progressively approaches zero. Reactant concentrations calculated for the stable steady state that may obtain are in satisfactory agreement with those observed experimentally, and the model accounts with surprising accuracy for experimentally observed effects of external orthophosphate on the steady‐state cycle activity and rate of starch production. Control analyses are reported which show that most of the non‐equilibrium enzymes in the system have a strong regulatory influence on the steady‐state level of all of the cycle intermediates. Substrate concentration control coefficients for cycle enzymes may be positive, such that an increase in activity of an enzyme may raise the steady‐state concentration of the substrate is consumes. Under optimal external conditions (0.15–0.5 mM orthophosphate), reaction flux in the Calvin cycle is controlled mainly by ATP synthetase and sedoheptulose bisphosphatase; the cycle activity approaches the maximum velocity that can be supported by the latter enzyme. At lower concentrations of external orthophosphate the cycle activity is controlled almost exclusively by the phosphate translocator. At high external orthophosphate concentrations the phosphate translocator resumes predominant control, but also other non‐equilibrium enzymes gain strong flux control with one notable exception: ribulosebisphosphate carboxylase has no significant regulatory influence on the cycle activity under conditions of light and CO2 saturation, nor does it control the concentration of any cycle intermediate other than its substrate. Copyright © 1988, Wiley Blackwell. All rights reserved</p>},
  author       = {Pettersson, Gösta and Ryde-Pettersson, Ulf},
  issn         = {0014-2956},
  language     = {eng},
  number       = {3},
  pages        = {661--672},
  publisher    = {Wiley-Blackwell},
  series       = {European Journal of Biochemistry},
  title        = {A mathematical model of the Calvin photosynthesis cycle},
  url          = {http://dx.doi.org/10.1111/j.1432-1033.1988.tb14242.x},
  volume       = {175},
  year         = {1988},
}