L-AraDH initiates the degradation of L-arabinose. Catalyzes the NAD(P)(+)-dependent conversion of L-arabinose to L-arabino-gamma-lactone. It is highly specific for L-arabinose as substrate and can use both NADP(+) and NAD(+) as electron acceptor, with a slight preference for NADP(+). alpha-L-arabinopyanose + NAD(+) = H(+) + L-arabinono-1,4-lactone + NADH alpha-L-arabinopyanose + NADP(+) = H(+) + L-arabinono-1,4-lactone + NADPH Optimum pH is 8.5. It shows 50% activity at pH values of 6 and 10. Optimum temperature is 45 degrees Celsius. Carbohydrate degradation; L-arabinose degradation via L-arabinono-1,4-lactone pathway. Homotetramer. Transcriptionally up-regulated by both L-arabinose and D-xylose via the pentose-specific regulator XacR. Cells lacking this gene lose the ability to grow on L-arabinose but not on D-xylose. Belongs to the NAD(P)-dependent epimerase/dehydratase family.