Involved in the non-phosphorylated metabolic pathway of L-rhamnose catabolism. Catalyzes the oxidation of L-rhamnose to yield L-rhamnono-1,4-lactone. It can also oxidize L-lyxose and L-mannose, and uses only NADP. L-rhamnofuranose + NADP(+) = H(+) + L-rhamnono-1,4-lactone + NADPH kcat is 1.341 min(-1) for dehydrogenase activity with L-rhamnose as substrate (at pH 7 and 60 degrees Celsius). kcat is 1.426 min(-1) for dehydrogenase activity with L-lyxose as substrate (at pH 7 and 60 degrees Celsius). kcat is 892.9 min(-1) for dehydrogenase activity with L-mannose as substrate (at pH 7 and 60 degrees Celsius). Optimum pH is 7. Optimum temperature is 60 degrees Celsius. Carbohydrate degradation; L-rhamnose degradation. Belongs to the short-chain dehydrogenases/reductases (SDR) family. Truncated N-terminus.