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Advances in Photosynthesis Fundamental Aspects Part 13

Tham khảo tài liệu 'advances in photosynthesis fundamental aspects part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 352 Advances in Photosynthesis - Fundamental Aspects where following notations are used x y and z are the RuBP CO2 and O2 concentrations respectively Kcca KO2 and KRuBP are the equilibrium constants of the reactions E RuBP CO E RuBP CO2 E RuBP O.2 E RuBP O2 and E RuBP E RuBP respectively. Two first equations in their simplified form Dubinsky et al. 2010 describe sugar x and CO2 y concentration variations. The third describes variations of O2 z concentration. In the set of equations Vc is the maximum rate of RuBP carboxylation Vox is the maximum rate of RuBP oxygenation. Vout is the maximum rate of sugar efflux Kout is the Michaelis constant of the pseudoenzyme by means of which sugars are removed from the system the real mechanism of sugars removal is certainly more complicated but it is the simplest way to describe the effect of sugar efflux saturation . kCO2 is the CO2 diffusion coefficient from the surrounding medium into a cell CO2out is the CO2 concentration in the medium kO2 is the O2 diffusion coefficient from the medium into the cell O2out is the O2 concentration in the medium. The solution of the system with cell parameters taken from the literature Dubinsky Ivlev 2011 results in establishing of counter-phase undamped oscillations with the period of 1 - 3 sec for CO2 and O2 and in respective oscillations of CO2 O2 ratio Fig. 5 . The oscillations could switch over Rubisco from carboxylase function to oxygenase and back. Fig. 5. The calculated photosynthetic oscillations of CO2 O2 concentration ratio according to the model described in the text. Thus the theoretical calculations proved the principal possibility of the existence of sustained oscillations in carbon metabolism of a photosynthesizing cell. Let s consider now how Calvin cycle works in different phases of photosynthetic oscillations from the point of 13C isotope distribution in metabolites. In carboxylase phase of oscillations Calvin cycle works as shown on Fig. 6. Due to carbon isotope effect in