Fructokinase deficiency

Higher in the blood of a person with a fructokinase deficiency than in the normal person... 

A number of other enzymopathic substances (e.g., pyruvate kinase. Chapter 13 and pyrimidine-5 -nucleotidase. Chapter 27), abnormal hemoglobins (Chapter 28), and abnormalities of the erythrocyte cytoskeleton (Chapter 10) may cause hemolytic anemia. Because many enzymes in the red cell are identical to those in other tissues, defects in these enzymes may have pleiotropic effects. Thus, in addition to hemolytic anemia, triose phosphate isomerase deficiency causes severe neuromuscular disease, and phospho-fructokinase deficiency causes a muscle glycogen storage disease (Chapter 13). Mutations that result in decreased enzyme stability are usually most strongly expressed in erythrocytes because of their inability to synthesize proteins. 

Familial fructokinase deficiency causes no symptoms because... 

Hepatic fructokinase deficiency (Fig. 22.3) is a rare, benign disorder in which fructose accumulates in the blood and urine. It is most commonly found in Jewish families and subjects have a normal hfe expectancy. Sometimes the fructose in the urine is confused with glucose and this can lead to an incorrect diagnosis of diabetes meUitus. 

Indications diagnosis of HFI and fructose-1,6-diphosphatase deficiency (fructokinase deficiency). 

Caution watch for hypoglycemia between 20 and 50 min. 25% i.v. glucose solution should be immediately available to abort hypoglycemia as needed. Nausea and abdominal pain are frequent in affected individuals. Interpretation decreased glucose and increased lactic acid, and uric acid together with a decrease of phosphate indicate HFI or fructose-1,6-diphos-phatase deficiency (in fructokinase deficiency a rise in fructose can be detected). 

Fructokinase deficiency and D-glyceric acidemia, however, have symptoms which are nonspecific and are often unimpressive. 

Figure 5 Model of phosphorus (P) deficiency-induced physiological changes associated with the release of P-mobilizing root exudates in cluster roots of white lupin. Solid lines indicate stimulation and dotted lines inhibition of biochemical reaction sequences or mclaholic pathways in response to P deliciency. For a detailed description see Sec. 4.1. Abbreviations SS = sucrose synthase FK = fructokinase PGM = phosphoglueomutase PEP = phosphoenol pyruvate PE PC = PEP-carboxylase MDH = malate dehydrogenase ME = malic enzyme CS = citrate synthase PDC = pyruvate decarboxylase ALDH — alcohol dehydrogenase E-4-P = erythrosc-4-phosphate DAMP = dihydraxyaceConephos-phate APase = acid phosphatase.

Genetic deficiency of fructokinase is benign and often detected incidentally when the urine is checked for glucose with a dipstick. Fructose 1-phosphate aldolase deficiency is a severe disease because of accumulation of fructose 1-phosphate in the liver and renal proximal tubules. Table 1-12-4 compares the two conditions. Symptoms are reversed after removing fructose and sucrose from the diet. 

Table 1-12-4. Comparison of Fructokinase and Fructose 1-Pho hate Aldolase Deficiencies...

Essential fructosuria is a benign, asymptomatic condition arising from deficiency of the enzyme fructokinase that causes a portion of fructose to be excreted in the urine. 

For values during an intravenous fructose tolerance test in controls and individuals with deficiencies of fructokinase, fructaldolase, and fructose- 1,6-bisphosphatase, see Steinmann et al. [36]. 

Cause and treatment of hereditary fructose intolerance A deficiency of fructokinase causes a benign condition, but a deficiency of aldolase B causes hereditary fructose intolerance, in which severe hypoglycemia and liver damage can lead to death if the amount of fructose (and, therefore, sucrose) in the diet are not severely limited. 

DHAP is a glycolysis intermediate, whereas glyceraldehyde must be reduced by a mitochondrial enzyme, glyceraldehyde dehydrogenase, to glycerol, which is then subject to action by glycerol kinase in the liver. The aldolase seems to be the principal pathway of metabolizing fructose and depends on the initial phosphorylation step catalyzed by fructokinase, which produces fructose-l-phosphate. Fructokinase is defective in an inherited disorder, essential fructosuria. Fructose-l-phosphate aldolase is deficient in the hereditary disorder fructose intolerance. 

Fructokinase is deficient in essential fructosuria therefore, fructose can-s not be metabolized as rapidly as it normally would. Blood fructose levels... 

In the liver, kidney, and intestine, fructose can be converted to glycolytic/ gluconeogenic intermediates by the actions of three enzymes—fructokinase, aldolase B, and triokinase (also called triose kinase)—as shovra in Figure 24-1. In these tissues, fructose is rapidly phosphorylated to fructose 1-phosphate (FIP) by fructokinase at the expense of a molecule of adenosine triphosphate (ATP). This has the effect of trapping fructose inside the cell. A deficiency in this enzyme leads to the rare but benign condition known as essential fmcto-suria. In other tissues such as muscle, adipose, and red blood cells, hexokinase can phosphorylate fructose to the glycolytic intermediate fmctose 6-phosphate (F6P). 

On entry into the microbial cell, sucrose is hydrolyzed by an induced sucrase, and the D-fructose obtained is phosphorylated by a specific, sucrose-induced fructokinase (ATP D-fructose 6-phosphotransferase, EC 2.7.1.4)176,177 (see Scheme 2). Mutants deficient in... 

Essential fructosuria which is a benign condition caused by a deficiency of the enzyme fructokinase. 

Essential fructosuria is an unrelated and completely harmless condition caused by deficiency of fructokinase [32]. 

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