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

A mechanistic model of photosynthesis is developed based on the characteristics of ribulose 1,5‐bisphosphate (RuBP) carboxylase and the assimilation of CO 2 as an ordered reaction with RuBP binding before CO 2 . An equation is derived which considers the effects of light (for regeneration of RuBP) and CO 2 . Taking values for the maximum turnover of RuBP carboxylase at substrate saturation, the maximum carboxylation efficiency (maximum increase in rate per increase in CO 2 concentration) and the minimum quantum requirement for the C 3 pathway, photosynthesis in the absence of photorespiration is simulated. In the model, at varying concentrations of CO 2 , 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 V max / K m CO2 ) as CO 2 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.