Galactolysis refers to the catabolism of galactose.

In the liver, galactose is converted through the Leloir pathway to glucose 6-phosphate[1] in the following reactions:

       galacto-                uridyl                phosphogluco-
        kinase               transferase                mutase
   gal --------> gal 1 P ------------------> glc 1 P -----------> glc 6 P
                            ^           \
                           /             v
                        UDP-glc       UDP-gal
                           ^             /
                            \___________/
                              epimerase

Mutations in the enzymes involved in galactolysis result in metabolic disorders.[2]

Metabolic disorders

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There are 3 types of galactosemia or galactose deficiencies:

Name Enzyme Description
galactokinase deficiency Galactokinase Causes cataracts, which form due to the elevation of galactitol that accumulates when galactose is metabolized in an alternative pathway that is not the Leloir pathway.[2] These are treatable by restricting galactose from the diet.
UDPgalactose-4-epimerase deficiency UDPgalactose-4-epimerase Is extremely rare (only 2 reported cases). It causes nerve deafness.
Galactose-1-phosphate uridyl transferase deficiency Galactose-1-phosphate uridyl transferase Is the most problematic, as galactose-free diets are not effective in treating neurocognitive deficiencies (in particular language disorders such as verbal dyspraxia) and ovarian failure. If a galactose-free diet is administered, cataracts and acute symptoms such as kidney and liver failure respond immediately. Formation of cataracts is similar to that in galactokinase deficiency.[2]

References

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  1. ^ Holden, Hazel M.; Rayment, Ivan; Thoden, James B. (7 November 2003). "Structure and Function of Enzymes of the Leloir Pathway for Galactose Metabolism". Journal of Biological Chemistry. 278 (45): 43885–43888. doi:10.1074/jbc.R300025200. PMID 12923184.
  2. ^ a b c Demirbas, Didem; Coelho, Ana I.; Rubio-Gozalbo, M. Estela; Berry, Gerard T. (June 2018). "Hereditary galactosemia". Metabolism. 83: 188–196. doi:10.1016/j.metabol.2018.01.025. PMID 29409891.