The global mass and average rate of rubisco

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 approximate to 0.7 Gt, more than an order of magnitude higher than previously thought. We find that > 90% of Rubisco enzymes are found in the approximate to 2 x 10(14) m(2) of leaves of terrestrial plants, and that Rubisco accounts for approximate to 3% of the total mass of leaves, which we estimate at approximate to 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 approximate to 0.03 s(-1) on land and approximate to 0.6 s(-1) in the ocean. Compared with the maximal catalytic rate observed in vitro at 25 degrees C, the effective rate in the wild is approximate to 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.