Dicarbonyl/L-xylulose reductase, also known as carbonyl reductase II, is an enzyme that in human is encoded by the DCXR gene located on chromosome 17.

The DCXR gene encodes a membrane protein that is approximately 34 kDa in size and composed of 224 amino acids. The protein is highly expressed in the kidney and localizes to the cytoplasmic membrane.^[1]

DCSR catalyzes the reduction of several L-xylylose as well as a number of pentoses, tetroses, trioses, alpha-dicarbonyl compounds. The enzyme is involved in carbohydrate metabolism, glucose metabolism, the uronate cycle and may play a role in the water absorption and cellular osmoregulation in the proximal renal tubules by producing xylitol.^[2]

In enzymology, an L-xylulose reductase (EC 1.1.1.10) is an enzyme that catalyzes the chemical reaction

xylitol + NADP⁺ ${\displaystyle \rightleftharpoons }$ L-xylulose + NADPH + H⁺

Thus, the two substrates of this enzyme are xylitol and NADP⁺, whereas its 3 products are L-xylulose, NADPH, and H⁺.

• Xylulose
• Xylitol (Note conversion of ketone to alcohol)

This enzyme belongs to the superfamily of short-chain oxidoreductases, specifically those acting on the CH-OH group of donor with NAD⁺ or NADP⁺ as acceptor. The systematic name of this enzyme class is xylitol:NADP⁺ 2-oxidoreductase (L-xylulose-forming).

A deficiency is responsible for pentosuria. The insufficiency of L-xylulose reductase activity causes an inborn error of metabolism disease characterized by excessive urinary excretion of L-xylulose.

Over-expression and ectopic expression of the protein may be associated with prostate adenocarcinoma.^[3]