A mechanistic model for photosynthesis based on the multisubstrate ordered reaction of ribulose 1,5 bisphosphate carboxylase

Abstract

Abstract. A mechanistic model of photosynthesis is developed based on the characteristics of ribulose 1,5‐bisphosphate (RuBP) carboxylase and the assimilation of CO2 as an ordered reaction with RuBP binding before CO2. An equation is derived which considers the effects of light (for regeneration of RuBP) and CO2. Taking values for the maximum turnover of RuBP carboxylase at substrate saturation, the maximum carboxylation efficiency (maximum increase in rate per increase in CO2 concentration) and the minimum quantum requirement for the C3 pathway, photosynthesis in the absence of photorespiration is simulated. In the model, at varying concentrations of CO2, the efficiency of light utilization approaches a maximum value as photon flux density decreases. Similarly, with a given maximum carboxyation capacity, at varying photon flux densities the carboxylation efficiency approaches a constant maximum value (equal to Vmax/KmCO2) as CO2 is decreased. However, a decrease in the state of activation of RuBP carboxylase under low light results in a lower carboxylation efficiency. Limits on the rate of photosynthesis, as the maximum capacity for regeneration of RuBP is reduced relative to carboxylation potential, or as the maximum capacity of the carboxylase varies, are considered.

Comprehensive classification and perspective for modelling photorespiratory metabolism

“…The actual rate of carboxylation, v c , is then no greater than min(w c ,J′). Using similar arguments, Farazdaghi & Edwards () determined the net rate of CO 2 assimilation in the absence of dark respiration.…”

“…The actual rate of carboxylation, v c , is then no greater than min(w c ,J′). Using similar arguments, Farazdaghi & Edwards (1988) determined the net rate of CO 2 assimilation in the absence of dark respiration. Sharkey (1985) introduced a third rate-limiting step for the Rubisco reaction, namely, triose phosphate (TP) utilisation.…”

A model for photosynthesis and photorespiration in C3 plants based on the biochemistry and stoichiometry of the pathways

“…lb ered ordered reactions, with RuBP binding flrst with Rubisco (Pierce, Lorimer & Reddy, 1986). This can be used as a basis for tnodelling the physiologieal response of plants to CO2 and light in the absence (Farazdaghi & Edwards, 1988) However, as three RuBP are produced for each 20, reacting with RuBP in the PCO cycle and for eaeh CO2 fixed ( Fig. 1 b).…”

“…This tteattnent is based on the assumption that photosynthesis is an ordered teaetion with RuBP binding first. Expressed in terms of Ihe tate of use of quanta and employing the Michaelis-Menten equation as tnodified by Farazdaghi & Edwards (1988), (5) where V^ is the rate of quantum u,sc in photosynthesis, Krr,q is the maxitnum rate of quantum use (dependent on capacity for PGA to RuBP conversion at saturating PGA and the eapaeity for photochetnistry), Ei, the fraction of Ught available for carbon assimilation, and /, the quantum flux density in /nnol quanta tn^ s ' (400-700 ntn).…”

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A model is developed for photosynthesis and photorespitation in C, plants, using an equation for the multisubstr-ate ordered reaction of ribulose 1,5-bisphosphate car-boxylase-oxygenase (Farazdaghi & Edwards, 1988). The model examines net CO, fixation with O, inhibition, and mutual inhibition when equilibrium exists between earboxylation and oxygenation (at the CO2 compensation point).

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