The Leloir pathway is a metabolic pathway for the catabolism of D-galactose into D-glucopyranose 6-phosphate named after Luis Federico Leloir . Since galactose cannot be directly used for glycolysis, it needs to be converted into a different form. This pathway starts in the cytosol and finishes in the chloroplast. First, aldose 1-epimerase is a predicted enzyme (coloured orange in the image) that is theorized to catalyze the conversion of beta-D-galactose into alpha-D-galactose. This enzyme has not yet been elucidated for Arabidopsis thaliana. Second, galactokinase catalyzes the conversion of alpha-D-galactose into alpha-D-galactose 1-phosphate. Third, D-galactose-1-phosphate uridylyltransferase is a predicted enzyme theorized to catalyze the reaction whereby alpha-D-galactose 1-phosphate and UDP-glucose is converted into alpha-D-glucopyranose 1-phosphate and UDP-galactose. This enzyme has not yet been elucidated in Arabidopsis thaliana. UDP-glucose and UDP-galactose can be interconverted by the enzyme UDP-glucose 4-epimerase which requires NAD as a cofactor. Alpha-D-glucopyranose 1-phosphate must then be imported into the chloroplast, by a yet not discovered alpha-D-glucopyranose 1-phosphate transporter. Last, phosphoglucomutase uses magnesium ion as a cofactor to convert alpha-D-glucopyranose 1-phosphate into D-glucopyranose 6-phosphate.

D-Galactose Degradation (Leloir pathway) References