Converts the aldose L-fucose into the corresponding ketose L-fuculose (PubMed:13319278, PubMed:4928018, PubMed:4632320, PubMed:8564401, PubMed:9367760). Also converts D-arabinose into D-ribulose (PubMed:13319278, PubMed:4928018, PubMed:4632320). In addition, catalyzes the isomerization of L-xylulose to L-xylose (PubMed:22133443). L-fucose = L-fuculose D-arabinose = D-ribulose L-xylopyranose = L-xylulose Can also use Co(2+). Inhibited by ribitol, L-arabitol and dulcitol (PubMed:4632320). Isomerization of L-xylulose to L-xylose is inhibited by xylitol (PubMed:22133443). kcat is 0.125 sec(-1) with L-xylulose as substrate. Optimum pH is 7.6-10.6 with L-fucose or D-arabinose as substrate. Optimum temperature is 50 degrees Celsius with L-xylulose as substrate. Carbohydrate degradation; L-fucose degradation; L-lactaldehyde and glycerone phosphate from L-fucose: step 1/3. Homohexamer. By L-fucose. Belongs to the L-fucose isomerase family.