Involved in the degradation of L-arabinose. Catalyzes the interconversion of L-ribulose 5-phosphate (LRu5P) and D-xylulose 5-phosphate (D-Xu5P) via a retroaldol/aldol mechanism (carbon-carbon bond cleavage analogous to a class II aldolase reaction). L-ribulose 5-phosphate = D-xylulose 5-phosphate Binds 1 zinc ion per subunit. Carbohydrate degradation; L-arabinose degradation via L-ribulose; D-xylulose 5-phosphate from L-arabinose (bacterial route): step 3/3. Belongs to the aldolase class II family. AraD/FucA subfamily.