Fructose and Galactose metabolism Fructose metabolism Essential fructosuria

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 Ø Lens (diabetic cataract) Ø 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 Ø galactosemia (Galactose 1 -phosphate uridylyltransferase deficiency) Ø genetic disease (AR, 1/60 000) Ø 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 Ø Conversion to intermediates of glycolysis Ø Genetic abnormalities, accumulation of intermediates, tissue damage Ø 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.