The first reaction of the non-cyclic photosynthetic process is catalyzed by Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), which carboxylase glyceraldehyde-3-phosphate with carbon dioxide to produce the Ribulose-1,5-bisphosphate
(RuBP). This reaction is the initial step in the Calvin cycle, also known as the light-independent or dark reaction of photosynthesis.
Rubisco is an enzyme found within the chloroplasts of plant cells and some bacteria. It is one of the most abundant proteins in the world and plays a crucial role in carbon fixation, the process by which carbon dioxide is converted into organic compounds.
In this reaction, Rubisco catalyzes the carboxylation of glyceraldehyde-3-phosphate (G3P) by carbon dioxide (CO2). G3P is a three-carbon compound produced during the Calvin cycle, and carbon dioxide is obtained from the surrounding environment.
The reaction is as follows:
Ribulose-1,5-bisphosphate (RuBP) + Carbon dioxide (CO2) → 2 molecules of 3-phosphoglycerate (3-PGA)
Rubisco acts as the catalyst in this reaction, facilitating the bonding of carbon dioxide to RuBP and forming an unstable intermediate that quickly breaks down into two molecules of 3-phosphoglycerate. These molecules will then go through a series of enzymatic steps to ultimately produce glucose and other organic compounds.
This carboxylation reaction is crucial for the overall process of photosynthesis as it allows plants to capture and convert carbon dioxide into usable energy in the form of glucose. Rubisco's role in this reaction makes it one of the most important enzymes in the biosphere and a key player in the Earth's carbon cycle.