The global mass and average rate of rubisco

Abstract

Photosynthetic carbon assimilation enables energy storage in the living world and produces most of the biomass in the biosphere. Rubisco (d-ribulose 1,5-bisphosphate carboxylase/oxygenase) is responsible for the vast majority of global carbon fixation and has been claimed to be the most abundant protein on Earth. Here we provide an updated and rigorous estimate for the total mass of Rubisco on Earth, concluding it is ≈0.7 Gt, more than an order of magnitude higher than previously thought. We find that >90% of Rubisco enzymes are found in the ≈2 × 1014m2of leaves of terrestrial plants, and that Rubisco accounts for ≈3% of the total mass of leaves, which we estimate at ≈30 Gt dry weight. We use our estimate for the total mass of Rubisco to derive the effective time-averaged catalytic rate of Rubisco of ≈0.03 s−1on land and ≈0.6 s−1in the ocean. Compared with the maximal catalytic rate observed in vitro at 25 °C, the effective rate in the wild is ≈100-fold slower on land and sevenfold slower in the ocean. The lower ambient temperature, and Rubisco not working at night, can explain most of the difference from laboratory conditions in the ocean but not on land, where quantification of many more factors on a global scale is needed. Our analysis helps sharpen the dramatic difference between laboratory and wild environments and between the terrestrial and marine environments.

Photorespiration in the context of Rubisco biochemistry, CO2 diffusion and metabolism

“…The value of is only c. 2–3 sec −1 in C 3 plants (Whitney et al , ), and is why Rubisco constitutes around 20–30% of soluble leaf protein, but may reach more than 50% depending on the growth conditions (Makino and Osmond, ; Galmés et al , ), corresponding to 10–25% of total leaf nitrogen (Onoda et al , ; Evans and Clarke, ). Its high abundance across all photosynthetic organisms means that Rubisco may be the most abundant protein on Earth (Ellis, ; Bar‐On and Milo, ). Both the slow turnover rate and the competitive inhibition by O 2 give Rubisco the reputation of being an inefficient enzyme.…”

Microalgal kinetics — a guideline for photobioreactor design and process development

“…Due to its tremendous importance, much research work has been carried out to measure kinetic parameters in vivo and in vitro. Isolated RuBisCo shows in vitro typical half-saturation constants of 740 to 1120 ppm = 0.074 to 0.112% for CO 2 (25-38 µM [51]) and maximum turnover rates of 4 s −1 [52]. This constant is a factor 2.1 to 3.2 higher than the measured value in vivo and a factor 1.8 to 2.8 higher than the atmospheric concentration, recently 400 ppm [equilibrium in water phase 0.04% ≈ 13.6 µmol⋅L −1 ≈ 0.6 mg⋅L −1 ].…”

Evolutionary trends in RuBisCO kinetics and their co‐evolution with CO2 concentrating mechanisms

“…RuBisCO catalyzes the addition of CO 2 to ribulose 1,5‐bisphosphate (RuBP), producing two molecules of 3‐phosphoglycerate, and the enzyme is characterized by a relatively low affinity for CO 2 and a slow carboxylation turnover rate ( k cat c ; about 1–10 reactions per second). This kinetic behaviour explains the large amounts of RuBisCO required to sustain effective net photosynthetic rates (Evans, ), and make RuBisCO one of the most abundant proteins on Earth (Ellis, ; Bar‐On and Milo, ). In addition, RuBisCO not only catalyzes the carboxylation of RuBP, but also its oxygenation.…”