RuBisCo is known as the most important and most abundant protein on Earth, since virtually all life depends directly or indirectly on it. This protein occurs in higher plants, lower plants and in a wide variety of photosynthetic bacteria. RuBisCo normally represents more than 50% of the protein in the leaves of higher plants, at least when referring to plants of type C3 *. Thanks to this protein, terrestrial plants fix about 500 trillion kg of carbon, but for this they need large amounts of RuBisCo. We can say that for each person on our planet there are about 10 kg of this protein in terrestrial plants.
* Note: there are plants of type C3, C4 and CAM that differ in the photosynthetic mechanisms, and the C3 require a lot of RuBisCo because in these the proteins are in contact with the oxygen that competes with CO2 as we will see later.
All organisms depend directly or indirectly on this protein. Autotrophic beings use RuBisCo to produce the energetic organic compounds they need and heterotrophic beings obtain these compounds from autotrophs.