RubisCO is present in the majority of autotrophic organisms, including prokaryotes such as photosynthetic and chemolithoautotrophic bacteria and archaea, as well as eukaryotic algae and higher plants. It is one of the most abundant proteins on Earth, estimated to be present in approximately 1 milligram of protein per kilogram of leaf tissue. Its mass is about 170 million Da; this makes it among the largest proteins known. The genome of Arabidopsis thaliana, which does not contain DNA related to ribosomes, contains a gene coding for a putative rubisco enzyme that spans about 11,000 base pairs of genomic DNA and encodes a polypeptide of 358 amino acids.
Although rubisco was first discovered in plants, it is also found in some bacteria and archaea. The enzymes are very similar to each other, with plant rubisco having three catalytic sites while bacterial rubisco only has two. This suggests that they evolved from a common ancestor gene through gene duplication and specialization. Although both plant and bacterial rubisco use the same substrate (ribulose-1,5-bisphosphate) and follow a similar reaction mechanism, they function differently due to their different active sites. Bacterial rubisco lacks an oxygen-containing group that interacts with the magnesium atom involved in catalysis by plant rubisco.
Ribulose Bisphosphate Carboxylase Oxygenase is abbreviated as RuBisCO. Ribulose bisphosphate (RuBP), a five-carbon ketose sugar, is used to make it. RuBisCO is the most common enzyme on the planet. As a result, RuBisCO acts as a carboxylase and attaches to plants to carry out more carboxylation. Oxygen is then released as water during the process of photosynthesis.
As an oxygenase, RuBisCO releases carbon dioxide and forms carbonyl groups with other molecules. It does this by rearranging molecular bonds very quickly and efficiently. For example, when RuBisCO binds with two molecules of ribulose bisphosphate, it produces three molecules of 2-C-carboxyarabinitol 1-5-bisphosphate. One molecule of CO2 is incorporated into each product molecule! This means that every time RuBisCO binds with two molecules of ribulose bisphosphate, it releases three molecules of CO2 into its environment.
RuBisCO has a large binding site that can accommodate multiple copies of ribulose bisphosphate. The structure of this binding site has been determined for several different species of bacteria and plants. It contains areas that are hydrophobic (not willing to wet) and areas that are hydrophilic (willing to wet). Water molecules cannot enter these binding sites because they are too tight. Instead, water is ejected from these sites when they bind with their ligands.
RuBisCO is physiologically significant because it catalyzes the principal chemical process that allows inorganic carbon to enter the biosphere. Unlike RuBisCO, phosphoenolpyruvate carboxylase only briefly fixes carbon. It does so in response to signals from other parts of the cell that help determine when and where photosynthesis will take place.
Furthermore, RuBisCO is also important because it is the target of many herbicides. This has led to a huge reduction in the amount of carbon being fixed by plants into biomass over recent years. Herbicide-resistant crops provide some protection against this effect, but they are not used everywhere yet. There is also interest in using microbes or other organisms's enzymes to produce chemicals or fuel instead. However these processes are still in their early stages of development.
Finally, RuBisCO is relevant to humans because it is one of the main targets of antimalarial drugs. Many compounds that inhibit Plasmodium falciparum RuBisCO activity have been discovered over the past few decades, with several now used in combination therapy against malaria.
These drugs can have serious side effects for humans too, since we also have RuBisCO in our bodies. The enzyme occurs naturally in algae and plants, and even some bacteria.
Similarly, RuBisCO, a crucial enzyme in photosynthesis in plants, is a "notoriously inefficient" enzyme. RuBisCO is in charge of absorbing inorganic carbon dioxide into plant metabolism; hence, nearly all of the carbon in the food we eat was generated via RuBisCO's activities. However, it can use only three out of four bonds available in organic carbon compounds, which means that almost all of the carbon is converted into glucose or some other compound that can be used by plants but not humans. This is why scientists think that evolution would have favored organisms that used their resources efficiently rather than those that accumulated toxic substances in their bodies while wasting the most efficient way to use energy.
Efficiency is also important because it allows species to grow larger sizes and live longer lives. The more efficient an organism is at using its limited resources, the greater its competitive advantage over others. This is one reason why biologists believe that evolution will always find a way around natural obstacles such as physical limitations on growth or life spans. For example, animals that live in habitats with few nutrients available only have their metabolic efficiency increased through evolutionary adaptations like gigantism (large size) or neoteny (juvenile traits) to escape extinction. Similarly, plants that reproduce quickly to fill empty spaces within their habitat will tend to have higher rates of mutation than those that don't reproduce as often and so are less likely to lose genetic information during replication.