High Quality Content by WIKIPEDIA articles! 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.