Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Alternative splicing of the ketohexokinase (fructokinase) gene generates a "central" predominantly hepatic isoform (ketohexokinase-C) and a more widely distributed ketohexokinase-A. Only the abundant hepatic isoform is known to possess activity, and no function is defined for the lower levels of ketohexokinase-A in peripheral tissues. Hepatic ketohexokinase deficiency causes the benign disorder essential fructosuria. The molecular basis of this has been defined in one family (compound heterozygosity for mutations Gly40Arg and Ala43Thr). Here we show that both ketohexokinase isoforms are indeed active. Ketohexokinase-A has much poorer substrate affinity than ketohexokinase-C for fructose but is considerably more thermostable. The Gly40Arg mutation seems null, rendering both ketohexokinase-A and ketohexokinase-C inactive and largely insoluble. The Ala43Thr mutant retains activity, but this mutation decreases the thermal stability of both ketohexokinase-A and ketohexokinase-C. At physiologic temperature, this results in significant loss of ketohexokinase-C activity but not of ketohexokinase-A. Affected individuals who carry both mutations therefore probably have a selective deficiency of hepatic ketohexokinase, with peripheral ketohexokinase-A being preserved. These findings raise the possibility that ketohexokinase-A serves an unknown physiologic function that remains intact in essential fructosuria. Further mutation analysis in this rare disorder could illuminate the question of whether ketohexokinase-A activity is, unlike that of ketohexokinase-C, physiologically indispensable.
Diabetes 2003 Sep
PMID:Properties of normal and mutant recombinant human ketohexokinases and implications for the pathogenesis of essential fructosuria. 1294 85

A molecular understanding of the unique aspects of dietary fructose metabolism may be the key to understanding and controlling the current epidemic of fructose-related obesity, diabetes and related adverse metabolic states in Western populations. Fructose catabolism is initiated by its phosphorylation to fructose 1-phosphate, which is performed by ketohexokinase (KHK). Here, the crystal structures of the two alternatively spliced isoforms of human ketohexokinase, hepatic KHK-C and the peripheral isoform KHK-A, and of the ternary complex of KHK-A with the substrate fructose and AMP-PNP are reported. The structure of the KHK-A ternary complex revealed an active site with both the substrate fructose and the ATP analogue in positions ready for phosphorylation following a reaction mechanism similar to that of the pfkB family of carbohydrate kinases. Hepatic KHK deficiency causes the benign disorder essential fructosuria. The effects of the disease-causing mutations (Gly40Arg and Ala43Thr) have been modelled in the context of the KHK structure.
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PMID:Structures of alternatively spliced isoforms of human ketohexokinase. 1923 42

Fructose is one of the main sweetening agents in the human diet and its ingestion is increasing globally. Dietary sugar has particular effects on those whose capacity to metabolize fructose is limited. If intolerance to carbohydrates is a frequent finding in children, inborn errors of carbohydrate metabolism are rare conditions. Three inborn errors are known in the pathway of fructose metabolism; (1) essential or benign fructosuria due to fructokinase deficiency; (2) hereditary fructose intolerance; and (3) fructose-1,6-bisphosphatase deficiency. In this review the focus is set on the description of the clinical symptoms and biochemical anomalies in the three inborn errors of metabolism. The potential toxic effects of fructose in healthy humans also are discussed. Studies conducted in patients with inborn errors of fructose metabolism helped to understand fructose metabolism and its potential toxicity in healthy human. Influence of fructose on the glycolytic pathway and on purine catabolism is the cause of hypoglycemia, lactic acidosis and hyperuricemia. The discovery that fructose-mediated generation of uric acid may have a causal role in diabetes and obesity provided new understandings into pathogenesis for these frequent diseases.
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PMID:Inborn Errors of Fructose Metabolism. What Can We Learn from Them? 2836 61