ATP + D-ribulose = ADP + D-ribulose 5-phosphate + H(+) ATP + L-ribulose = ADP + H(+) + L-ribulose 5-phosphate Carbohydrate degradation; L-arabinose degradation via L-ribulose; D-xylulose 5-phosphate from L-arabinose (bacterial route): step 2/3. Belongs to the ribulokinase family.