Fructoses metabolism

Fructose may appear in the urine after eating fruits, honey, and syrups, but has no significance in these circumstances. Three disorders of fructose metabolism, inherited as autosomal recessive traits, produce fructosuria. 

This rare and harmless defect is due to a lack of fructokinase. Hereditary Fructose Intolerance 

A deficiency of fructose-1-phosphate aldolase produces this rare disorder with hypoglycemia and liver failure. Fructose ingestion inhibits glycogenolysis and giuconeogenesis, producing hypoglycemia. Early detection is important because this condition responds to a diet devoid of sucrose and fructose. 

Patients with this deficiency have episodes of apnea and hyperventilation and hypoglycemia, ketosis, and lactic acidosis caused by severe impairment of giuconeogenesis. Diagnosis is by demonstrating the enzyme defect in liver biopsy specimens. 

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Defects in Fructose Metabolism Cause Disease (Figure 20-5)... 

Van den Berghe G Inborn errors of fructose metabolism. Annu Rev Nutr 1994 l4 4l. 

Fructose is converted to fructose 6-phosphate by hexo-kinase, which phosphorylates both glucose and fructose. It then is converted to pyruvate via glycolysis, which is converted to acetyl-coenzyme-A in the mitochondria for oxidation by the Krebs cycle. The enzyme that is specific for fructose metabolism, fructokinase, has not been found in... 

Steinmann B, Gitzelmann R, Van den Berghe G (2001) Disorders of fructose metabolism. In Scriver CR, Beaudet AL, Sly WS, Valle D (eds) The Metabolic and Molecular Bases of Inherited Disease, 8th edn. McGraw-Hill, New York, pp 1489-1520... 

Galactose and fructose metabolism as part of the essential pathways of energy metabolism (see Figure 8.2, p. 90, for a more detailed view of the overall reactions of metabolism). 

The rate of fructose metabolism is more rapid than that of glucose because the trioses formed from fructose 1 -phosphate bypass phosphofructokinase—the major rate-limiting step in glycolysis (see p. 97). [Note Loading the liver with fructose, for example, by intravenous infusion, can significantly elevate the rate of lipogenesis, caused by the enhanced production of acetyl CoA.]... 

Palyza V, Bockova M. Poruchy metabolismu fruktozy a infuze. [Fructose metabolism disorders and infusions.] Vnitr Lek 1992 38(8) 814-21. 

Edelman, J. and Jefford, T.G., The mechanism of fructose metabolism in higher plants as exemplified by Helianthus tuberosus, New Phytol., 67, 517-531, 1968. 

Racker E. Alternate pathways of glucose and fructose metabolism. 

Deficiency in fructose metabolism, as in essential fme-tosuria, may be perfectly benign, for one is not interrupting the main line of the glycolytic chain. However, there is one condition, hereditary fructose intolerance, which does cause significant problems. 

Figure 16.15. Fructose Metabolism. Fructose enters the glycolytic pathway in the liver through the fructose 1-phosphate pathway.

Gopher, A-, Vaisman, N-, Mandel, H., and Lapidot, A. (1990). iDctermioation of fructose metabolism pathways in normal and fructose-intolerant children. Proc. Natl. Acad. Sci-U.S.A. 87, 5449-545.i... 

Gelfand, R. A., and Sherwin, R. S. (1986). Nitrogen conservation in starvation revisited Protein sparing with intravenous fructose. Metabolism 35, 37-44. 

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