RuBP carboxylase-oxygenase, commonly known as Rubisco, is the enzyme responsible for the first major step of carbon fixation in photosynthesis, where carbon dioxide is converted into energy-rich molecules. Due to its critical role in supporting virtually all life on Earth (by producing the organic matter that fuels ecosystems) and its relatively slow catalytic rate (requiring plants to synthesize large quantities), Rubisco is considered the most abundant enzyme in plants and on Earth overall.