The CO2/O2 specificity of ribulose 1,5-bisphosphate carboxylase/oxygenase

Abstract

The substrate specificity factor, V cKo/VoKc, of spinach (Spinacia oleracea L.) ribulose 1,5-bisphosphate carboxylase/oxygenase was determined at ribulosebisphosphate concentrations between 0.63 and 200 μM, at pH values between 7.4 and 8.9, and at temperatures in the range of 5° C to 40° C. The CO2/O2 specificity was the same at all ribulosebisphosphate concentrations and largely independent of pH. With increasing temperature, the specificity decreased from values of about 160 at 5° C to about 50 at 40° C. The primary effects of temperature were on K c [Km(CO2)] and V c [Vmax (CO2)], which increased by factors of about 10 and 20, respectively, over the temperature range examined. In contrast, K o [Ki (O2)] was unchanged and V o [Vmax (O2)] increased by a factor of 5 over these temperatures. The CO2 compensation concentrations (Γ) were calculated from specificity values obtained at temperatures between 5° C and 40° C, and were compared with literature values of Γ. Quantitative agreement was found for the calculated and measured Γ values. The observations reported here indicate that the temperature response of ribulose 1,5-bisphosphate carboxylase/oxygenase kinetic parameters accounts for two-thirds of the temperature dependence of the photorespiration/photosynthesis ratio in C3 plants, with the remaining one-third the consequence of differential temperature effects on the solubilities of CO2 and O2.

Effects of O2 and CO2 Concentrations on Quantum Yields of Photosystems I and II in Tobacco Leaf Tissue

“…For a constant and relatively low CO (<400 ,bar), an increase in gas phase [02] results in a decline in net CO2 flux from the atmosphere into the leaf. This is caused predominantly by oxygenation of RuBP and consequent internal release of CO2 during photorespiration (13 Figure 5 also reflect variation in the 4b, as shown in Figure 6. At low levels of 02 (1.6%), photorespiration is suppressed so that measurements of CO2 uptake provide a reasonable estimate of coupled noncyclic photosynthetic electron transport.…”

Improved temperature response functions for models of Rubisco-limited photosynthesis

“…The temperature dependence of V o,max has been assumed to be a constant proportion of V c,max over a range of temperature at 0·21 ¥ V c,max (Farquhar et al 1980;Farquhar & von Caemmerer 1982) though numerous values ranging from 0·19 to 0·77 ¥ V c,max have been determined (Badger & Andrews 1974;Badger & Collatz 1977;Jordon & Ogren 1981, 1984Makino, Mae & Ohira 1988;Whitney et al 1999;von Caemmerer 2000). Although numerous studies report values for the ratio of V o,max /V c,max at 25°C, very few studies have determined the temperature response of this ratio.…”

Elucidating Rice Cell Metabolism under Flooding and Drought Stresses Using Flux-Based Modeling and Analysis

“…Photorespiration in rice leaf cells was simulated by maximizing the straw biomass equation while constraining the photon uptake rate at 100 mmol g 21 dry cell weight d 21 and fixing the carboxylation-tooxygenation flux ratio (V C /V O ) of Rubisco with a value between 1 and 10. Here, it should be noted that the simulations with V C /V O ratios greater than or equal to 3 represent photorespiration under normal conditions, while any lesser value corresponds to the drought conditions (Jordan and Ogren, 1984). Again, the Boolean gene regulatory rules were also utilized to consider active reactions in the leaf cells (Supplemental Data File S3).…”

“…This oxygenase side reaction of Rubisco produces one molecule of 3-phosphoglycerate (3-PGA) and one molecule of 2-phosphoglycolate (2-PG) for each molecule of oxygen fixed. Of these, 2-PG is a wasteful by-product, requiring sufficient amounts of energy for its salvation into 3-PGA through a series of enzymatic steps known as "the photorespiratory cycle" (Jordan and Ogren, 1984). In addition, the amount of CO 2 available for photosynthesis is drastically reduced under drought conditions owing to the partial/full closure of leaf stomata, resulting in increased photorespiration (de Carvalho, 2008).…”