Ribulose-1 ,5 - bisphosphate carboxylase oxygenase , better known as RuBisCO , is an enzyme that catalyzes the first major step of carbon fixation in the Calvin cycle . Carbon fixation is a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as glucose . Ribulose-1 ,5 - bisphosphate carboxylase oxygenase , most commonly known by the shorter name RuBisCO , is an enzyme involved in the Calvin cycle that catalyzes the first major step of carbon fixation , a process by which the atoms of atmospheric carbon dioxide are made available to organisms in the form of energy-rich molecules such as glucose .