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. Transcription is repressed by glucose and by the binding of AraR to the operon promoter. L-arabinose acts as an inducer by inhibiting the binding of AraR to the DNA, thus allowing expression of the gene. Belongs to the ribulokinase family.