Catalyzes the interconversion of L-rhamnose and L-rhamnulose (PubMed:14243758, PubMed:2558952, PubMed:8564401, PubMed:1650346). Can also catalyze the isomerization of L-lyxose to L-xylulose (PubMed:1650346). L-rhamnopyranose = L-rhamnulose L-lyxopyranose = L-xylulose Binds 1 Mn(2+) ion per subunit. Optimum pH is 7.6. Carbohydrate degradation; L-rhamnose degradation; glycerone phosphate from L-rhamnose: step 1/3. Homotetramer. Induced by L-rhamnose via the RhaR-RhaS regulatory cascade. Binding of the cAMP receptor protein (CRP) is required for full expression (PubMed:10852886, PubMed:8230210). Also induced by L-lyxose (PubMed:1650346). In the crystal structure, RhaA appears to bind a zinc ion at a structural site. However, the metal ion may be different in vivo. Belongs to the rhamnose isomerase family.