Fructose hepatic

The digestible dietary carbohydrates yield glucose, galactose, and fructose that are transported via the hepatic portal vein to the hver where galactose and fructose are readily converted to glucose (Chapter 20). 

It is a semisynthetic disaccharide of fructose and lactose. It is not digested or absorbed in small intestine thereby withdrawing water into bowel lumen. It breaks down in colon to form more osmotically active products. It also causes reduction in ammonia in hepatic coma. 

Fructose 1-phosphate aldolase B Hereditary fructose intolerance, vomiting, lethargy, failure to thrive, hepatic failure good prognosis with early diagnosis and fructose restriction... 

Baker L, Winegrad AI (1970) Fasting hypoglycaemia and metabolic acidosis associated with deficiency of hepatic fructose-1,6-diphosphatase activity. Lancet ii 13 16... 

Early studies of the stimulatory effects of glucagon on hepatic gluconeogenesis using different gluconeogenic substrates and measuring the changes in the concentrations of intermediary metabolites identified the substrate cycles between pyruvate and P-enolpyruvate and between fructose-1,6-P2 and fructose-6-P as major sites of... 

Shin DJ and McGrane MM (1997) Vitamin A regulates genes involved in hepatic gluconeogenesis in mice phosphoenolpyruvate carhoxykinase, fructose-1,6-his-phosphatase and 6-phosphofructo-2-kinase/fructose-2,6-hisphosphatase./ourna/o/ Nutrition 127,1274-8. 

Wilson s disease, haemochromatosis, galactosaemia, glycogenosis type IV, ai-antitrypsin deficiency, tyrosin-aemia, idiopathic neonatal hepatitis, Niemann-Pick disease, Gaucher s disease, fructose intolerance, defective urea cycle, etc. 

Yoim, J. H., Kaslow, H. R., and Bergman, R. N. (1987). Fructose effect to suppress hepatic glycogen degradation. /. Biol Chem. 262,11470-11477. 

Liver. - The detailed mapping of glucose and lactate metabolism along the radius of the hepatic lobule has been investigated in situ in rat livers perfused with 1.5 mM lactate before and during perfusion with 5 mM fructose. 

Phosphorylation is regulated by insulin and glucagon. Diabetes mellitus (in which the ratio of glucagon to insulin is increased) and glucagon therapy reduce the hepatic activity of PFK-2 and increase that of FBPase-2. The concentration of fructose-2,6-bisphosphate is thus reduced, thereby stimulating gluconeogenesis. 

Aldolase allows both ol the triose phosphates DHAP and glyceraldehyde-3-phosphate to condense and lorm fructose-1,6-bisphosphate. In this manner, aldolase allows adipocyte glycerol to enter hepatic gluconeogenesis. 

Summary A 3-year-old boy with failure to thrive and possible hepatic failure. He presents with hypoglycemia and recurrent episodes of nausea and vomiting after ingestion of foods high in fructose. 

Biochemical basis of disorder Because of a genetic disorder, the hepatic aldolase B enzyme is defective, and functions normally in glycolysis but not in fructose metabolism. Glucose production is inhibited by elevated fructose 1-phosphate. When fructose is ingested, severe hypoglycemia results. 

Fructose 1-phosphate is further metabolized to dihydroxyacetone phosphate (DHAP) and glyceraldehyde by the hepatic isoform of the enzyme aldolase, which catalyzes a reversible aldol condensation reaction. Aldolase is present in three different isoforms. Aldolase A is present in greatest concentrations in the skeletal muscle, whereas the B isoform predominates in the liver, kidney, and intestine. Aldolase C is the brain isoform. Aldolase B has similar activity for either fructose 1,6-bisphosphate (F16BP) or FIP however, the A or C isoforms are only slightly active when FIP is the substrate. 

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