Figure 4.
Overview of galactose metabolism. The major pathway of galactose metabolism (the Leloir pathway) operates via the enzymes galactokinase (GALK), galactose-1-phosphate uridylyltransferase (GALT), and uridine diphosphate (UDP) galactose 4-epimerase (GALE), resulting in UDP-glucose. The conversion to galactitol by aldose reductase via the polyol pathway results in decreased availability of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione, with increased production of free radicals (56). By way of a nonenzymatic reaction with amino groups in proteins, lipids, and nucleic acids, galactose is converted to advanced glycation end products (AGEs).