Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.3.5.1 (succinate dehydrogenase)
 8,177 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Physiologically, a postprandial glucose rise induces metabolic signal sequences that use several steps in common in both the pancreas and peripheral tissues but result in different events due to specialized tissue functions. Glucose transport performed by tissue-specific glucose transporters is, in general, not rate limiting. The next step is phosphorylation of glucose by cell-specific hexokinases. In the beta-cell, glucokinase (or hexokinase IV) is activated upon binding to a pore protein in the outer mitochondrial membrane at contact sites between outer and inner membranes. The same mechanism applies for hexokinase II in skeletal muscle and adipose tissue. The activation of hexokinases depends on a contact site-specific structure of the pore, which is voltage-dependent and influenced by the electric potential of the inner mitochondrial membrane. Mitochondria lacking a membrane potential because of defects in the respiratory chain would thus not be able to increase the glucose-phosphorylating enzyme activity over basal state. Binding and activation of hexokinases to mitochondrial contact sites lead to an acceleration of the formation of both ADP and glucose-6-phosphate (G-6-P). ADP directly enters the mitochondrion and stimulates mitochondrial oxidative phosphorylation. G-6-P is an important intermediate of energy metabolism at the switch position between glycolysis, glycogen synthesis, and the pentose-phosphate shunt. Initiated by blood glucose elevation, mitochondrial oxidative phosphorylation is accelerated in a concerted action coupling glycolysis to mitochondrial metabolism at three different points: first, through NADH transfer to the respiratory chain complex I via the malate/aspartate shuttle; second, by providing FADH2 to complex II through the glycerol-phosphate/dihydroxy-acetone-phosphate cycle; and third, by the action of hexo(gluco)kinases providing ADP for complex V, the ATP synthetase. As cytosolic and mitochondrial isozymes of creatine kinase (CK) are observed in insulinoma cells, the phosphocreatine (CrP) shuttle, working in brain and muscle, may also be involved in signaling glucose-induced insulin secretion in beta-cells. An interplay between the plasma membrane-bound CK and the mitochondrial CK could provide a mechanism to increase ATP locally at the KATP channels, coordinated to the activity of mitochondrial CrP production. Closure of the KATP channels by ATP would lead to an increase of cytosolic and, even more, mitochondrial calcium and finally to insulin secretion. Thus in beta-cells, glucose, via bound glucokinase, stimulates mitochondrial CrP synthesis. The same signaling sequence is used in the opposite direction in muscle during exercise when high ATP turnover increases the creatine level that stimulates mitochondrial ATP synthesis and glucose phosphorylation via hexokinase. Furthermore, this cytosolic/mitochondrial cross-talk is also involved in activation of muscle glycogen synthesis by glucose. The activity of mitochondrially bound hexokinase provides G-6-P and stimulates UTP production through mitochondrial nucleoside diphosphate kinase. Pathophysiologically, there are at least two genetically different forms of diabetes linked to energy metabolism: the first example is one form of maturity-onset diabetes of the young (MODY2), an autosomal dominant disorder caused by point mutations of the glucokinase gene; the second example is several forms of mitochondrial diabetes caused by point and length mutations of the mitochondrial DNA (mtDNA) that encodes several subunits of the respiratory chain complexes. Because the mtDNA is vulnerable and accumulates point and length mutations during aging, it is likely to contribute to the manifestation of some forms of NIDDM.(ABSTRACT TRUNCATED)
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PMID:Mitochondria and diabetes. Genetic, biochemical, and clinical implications of the cellular energy circuit. 854 53

We encountered a patient with diabetes mellitus due to the 3243 mitochondrial tRNA mutation(DM-Mt3243), who developed insulin edema and hepatic dysfunction after starting insulin. Such a rare phenomenon was unlikely to be a fortuitous coincidence in mitochondrial diabetes, as none in 197 non-mutant NIDDM patients had same episode. Moreover, similar leg edema was noticed in another DM-Mt3243 patient, and other two DM-Mt3243 patients had leg edema which responded to coenzyme Q10. These observations suggest further a role of mitochondrial function on leg edema. The mechanism of his insulin edema may involve vasomotor changes induced by the rapidly glycemic control, because our case of insulin edema had a prominent increase of strong succinate dehydrogenase reactive vessels. Alternatively, myocardial dysfunction might have produced leg edema and hepatic dysfunction, because he had subclinical myocardial dysfunction, judged by imaging with beta-methyl-p-(123I)-iodophenyl-pentadecanoic acid. The third explanation is that a rapid improvement of glycemic control might have induced hepatic reoxygenation and the production of reactive oxygen species in the liver that contributed to cell damage. Thus, although we cannot draw definite conclusion, our experiences here suggest that mitochondrial dysfunction is important in the etiology of insulin edema.
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PMID:Insulin edema in diabetes mellitus associated with the 3243 mitochondrial tRNA(Leu(UUR)) mutation; case reports. 859 1

The enzyme activities of mitochondrial glycerol phosphate dehydrogenase (mGPD) (EC 1.1.99.5) and pyruvate carboxylase (PC) (EC 6.4.1.1) have been reported to be low in the pancreatic islet of several rodent models of NIDDM. The present study was undertaken to discern whether mGPD is abnormal in the Zucker diabetic fatty (ZDF) rat (ZDF/Gmi-fa/fa), an animal model of NIDDM in which insulin secretion is unable to counteract the insulin resistance associated with the obesity that characterizes this model. Experiments were performed in prediabetic 6-week-old ZDF rats in comparison with 12-week-old overtly hyperglycemic animals and, as controls, Zucker lean (ZL) rats (ZDF/Gmi-+/fa or -+/+) and Wistar rats (+/+) of the same ages. The enzyme activity of mGPD was 32 and 18% of normal in islets of 6- and 12-week-old ZDF rats, respectively (P < 0.001 by analysis of variance). The activity of PC, which like mGPD is relatively abundant in the pancreatic islet, was 17 and 10% of normal in the islets of 6- and 12-week-old ZDF rats, respectively (P < 0.001). The activity of mGPD was normal in islets from ZL rats. However, PC activity was slightly lower in islets of 6- (51% of normal, P = 0.007) and 12-week-old (67% of normal, P = 0.01) ZL rats. The amounts of mGPD protein, as judged from Western analysis, and of PC protein, as judged from probing transblots with streptavidin that binds to biotin-containing enzymes, roughly correlated with the enzyme activities. This indicates that the decreased enzyme activities are caused by the decreased net synthesis of these enzymes rather than by the decreased activity of a normal amount of enzyme. The enzyme activity of succinate dehydrogenase, a control for mGPD, was normal in the ZL and ZDF rats. An incidental finding of the current study was the discovery of beta-methylcrotonyl-CoA carboxylase and propionyl-CoA carboxylase in the islet. Levels of these enzymes were also normal. Although reductions in mGPD and PC may contribute to the abnormal insulin secretion present in overt diabetes, they are modest compared with the severe reductions seen in inherited inborn errors of metabolism. Because of this and because more than a single enzyme is affected and the enzymes in the islet are diminished in more than one rodent model of NIDDM, these reductions are unlikely to represent the primary genetic defect in the ZDF rat. Since ZDF rats are euglycemic at 6 weeks of age and ZL animals are euglycemic throughout life and since these animals demonstrate low enzyme activities, this evidence suggests that it is not hyperglycemia but rather some other component of the diabetic syndrome that is responsible for the reductions in these enzymes.
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PMID:Low mitochondrial glycerol phosphate dehydrogenase and pyruvate carboxylase in pancreatic islets of Zucker diabetic fatty rats. 886 70

Changes in the pancreas of diabetic patients with the A-to-G mitochondrial DNA (mtDNA) mutation at nucleotide position 3243 base pair (bp) have not previously been described. The clinical phenotypes of diabetes associated with the mtDNA 3243 mutation range from NIDDM to IDDM. We sought the presence of the mutation and studied volume of beta-, alpha-, and delta-cells, mitochondrial enzyme activity, and presence of apoptosis in diabetic pancreases obtained at autopsy. Pancreases were obtained from 16 patients with IDDM, from 18 patients with NIDDM, and from 11 nondiabetic patients. Mitochondrial enzyme activity was determined for cytochrome c oxidase (COX), the subunits of which are partially encoded by mtDNA, and for succinate dehydrogenase (SDH), the subunits of which are solely encoded by nuclear DNA. The volumes of islet beta-, alpha-, and delta-cells were estimated by computerized morphometry. Pancreatic cells were examined for apoptosis by an in situ end-labeling procedure. The mtDNA 3243 mutation was detected in 1 of 16 (6%) pancreases from the IDDM patients; none of the pancreases from 18 NIDDM patients and 11 nondiabetic patients had the mutation. The single patient with the mtDNA 3243 mutation was a 56-year-old woman with IDDM, aged 39 years at diabetes onset, whose mother was diagnosed with NIDDM. The patient had a history of secondary failure of oral hypoglycemic agents and had a marked decrease in the number of beta-cells. The islet beta-cells and non-beta-cells of the patient showed extremely decreased COX enzyme activity. The islet cells in the patient showed a high activity when examined for SDH. Some pancreatic exocrine cells also showed decreased COX activity with high SDH activity. In IDDM, NIDDM, and nondiabetic patients without the mtDNA 3243 mutation, only weak staining for SDH of the islet cells showed. The percentage of heteroplasmy of the mtDNA 3243 mutation in pancreatic micropunched islet specimens was 63 +/- 5% (mean +/- SD) in the islets, 32 +/- 3% in the exocrine pancreas, and 8 +/- 1% in peripheral polymorphonuclear cells. Apoptotic cells were not observed in the IDDM pancreas in the patient with the mtDNA 3243 mutation. The fact that higher levels of mutated mtDNA at 3243 bp were found in affected islets rather than in other tissue suggests that the distribution of the mutant may determine the effect on islet function. A characteristic decrease in the mitochondrial enzyme with COX activity and accelerated SDH activity of the affected islets may provide new insights into the pathogenesis of mitochondrial diabetes.
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PMID:In situ characterization of islets in diabetes with a mitochondrial DNA mutation at nucleotide position 3243. 931 51