The most important carboxylase in plants is ribulose bishosphate carboxylase (rubisco), which catalyzes the carboxyation of ribulose bisphosphate, the ‘carbon-fixing’ first step in the Calvin cycle. 在植物中最重要的羧化酶是核酮糖二磷酸羧化酶，它可以羧化核酮糖二磷酸，在卡尔文循环中是二氧化碳固定的第一步。
Ribulose is a ketopentose — a monosaccharide containing five carbon atoms, and including a ketone functional group. It has chemical formula C5H10O5. Two enantiomers are possible, D-ribulose (D-erythro-pentulose) and L-ribulose (L-erythro-pentulose). D-Ribulose is the diastereomer of D-xylulose.