sentences:  Galactose is also a substrate for the polyol pathway, but the corresponding keto sugar is not produced because sorbitol dehydrogenase is incapable of oxidizing galactitol.Nevertheless, aldose reductase can catalyze the reduction of galactose to galactitol
  
  The aldose reductase reaction, in particular the sorbitol produced, is important for the function of various organs in the body.For example, it is generally used as the first step in a synthesis of fructose from glucose; the second step is the oxidation of sorbitol to fructose catalyzed by sorbitol dehydrogenase.