Fructose and Galactose
metabolism
Fructose metabolism
Essential fructosuria
Hereditary fructose
intolerance
Principally in the liver (small intestine, kidney)
Aldolase B: low affinity for fructose 1-phosphate
(→ accumulation of fructose 1-phosphate in the liver )
The polyol pathway
Seminal vesicles (spermatozoa use fructose)
Accumulation of sorbitol in diabetic patients
 Lens (diabetic cataract)
 Muscles, nerves (periferal neuropathy)
Galactose metabolism:
Lens metabolism:
Diabetic cataract :
↑glucose concentration in the lens → ↑aldose reductase activity → sorbitol
accumulation → ↑osmolarity, structural changes of proteins
Clinical correlations:
A newborn: failure to thrive, vomiting and diarrhea after milk
 galactosemia (Galactose 1-phosphate uridylyltransferase
deficiency)
 genetic disease (AR, 1/60 000)
 hepatomegaly, jaundice, cataracts, mental retargation, death
Management: early diagnose, elimination of galactose from the diet
(artificial milk from soybean hydrolysate)
Summary:
Fructose and Galactose metabolism
 Conversion to intermediates of glycolysis
 Genetic abnormalities, accumulation of intermediates, tissue
damage
 Accumulation of sorbitol in diabetes
Pictures used in the presentation:
Marks´ Basic Medical Biochemistry A Clinical Approach, third edition, 2009 (M.
Lieberman, A.D. Marks)
Textbook of Biochemistry with Clinical Correlations, sixth edition, 2006 (T.M. Devlin)
Uronic acid Pathway
It is another minor alternative pathway for
glucose oxidation by which glucuronic acid,
ascorbic acid and pentoses are obtained
from glucose.
Like HMP shunt, it does not need nor
generate ATP.
Site:
In cytosol of many tissues, especially liver,
kidney and intestine.
Biological importance of Uronic Acid
Pathway:
1-Production of UDP-glucuronic acid, which is
the metabolically active form of glucuronic acid
which enters in:
• Synthesis of mucopolysaccharides.
• Detoxification by conjugation: UDP-glucuronic acid
is used to detoxify steroid hormones, drugs and
toxins.
• Formation of conjugated bilirubin.
2-Formation of pentoses.
3-Formation of vitamin C in plants and animal
except man and guinea pigs.