RubisCO

RUBISCO is the common name of ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme that is used in the Calvin cycle to catalyze the first major step of carbon fixation. RUBISCO catalyzes either the carboxylation or oxygenation of ribulose-1,5-bisphosphate (also known as RuBP) with carbon dioxide or oxygen.

RUBISCO is very important because it represents the most important pathway by which inorganic carbon enters the biosphere. It is also said that RUBISCO, which accounts for about 50% of all proteins found in leaves, is the most abundant protein on Earth.

RUBISCO is only active during the day. This activity is controlled in two ways:

1. During photosynthesis, the pH of the stroma rises from 7.0 to 8.0 because of the proton gradient created in the lumen. RUBISCO has a narrow optimal pH at 8.0.
2. In darkness, RUBISCO is inhibited by a competitive inhibitor sythesized by the plant.

External links

• Rubisco: Protein Data Bank entry
• The Plant Kingdoms sloth: Protein spotlight article on the "slothful" enzyme Rubisco