Catalyzes ATP-dependent phosphorylation of D-ribulose at C-5 to form D-ribulose 5-phosphate. Postulated to function in a metabolite repair mechanism by preventing toxic accumulation of free D-ribulose formed by non-specific phosphatase activities. Alternatively, may play a role in regulating D-ribulose 5-phosphate recycling in the pentose phosphate pathway. Can phosphorylate ribitol with low efficiency. ATP + D-ribulose = ADP + D-ribulose 5-phosphate + H(+) Carbohydrate metabolism; pentose and glucuronate interconversion. Expressed in kidney, lung and small intestine and to a lower extent in liver and detected in cerebrospinal fluid (at protein level). Expressed in fetal brain (at protein level). Disease susceptibility is associated with variants affecting the gene represented in this entry. Belongs to the FGGY kinase family.