Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.1.1 (hexokinase)
5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have adapted for glucose determination a new approach to kinetic analyses [Anal. Chem. 50, 1611 (1978)]; it is 50-fold less dependent upon some experimental variables than is a more conventional rate method. Modification of a commercially available hexokinase/glucose-6-phosphate dehydrogenase reagent system for glucose provides that the rate of production of NADH be first-order in total glucose concentration within about 30 s after sample and reagent are mixed. In the kinetic method, absorbance vs. time data recorded after 30 s and a multiple-linear-regression program are used to compute the absorbance change that would occur if the reaction were monitored to completion. Results demonstrate a linear relationship between glucose concentration and computed absorbance change. Application of the method to 51 human sera without rigorous control of either temperature or reagent composition yielded a regression equation of y = 1.01x -0.3 when kinetic results (y) were compared with equilibrium results (x) for the same samples analyzed in a hospital laboratory.
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PMID:A kinetic method for glucose that is insensitive to variations in temperature and enzyme activity. 46 84

In this communication the results of applying various histochemical semipermeable membrane techniques to the localization of several enzymes in bovine and porcine heart are presented. The Purkinje fibers of the atrioventricular conducting system of the bovine heart differ from the myocardium proper in containing a greater activity of the glycolytic and gluconeogenetic enzymes--lactate dehydrogenase, glyceraldehyde-phosphate dehydrogenase, hexokinase, glucosephosphate isomerase and phosphoglucomutase, and less activity of the aerobic enzymes--NADH: nitroBT oxidoreductase and isocitrate dehydrogenase (NADP+). The metabolic reactions obtained with Purkinje fibers of the porcine heart are less pronounced. These histochemical findings are in accordance with the impression that Purkinje fibers, compared with the common myocardial fibers, have a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism. The activity of the NADPH regenerating enzymes glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating), and the activity of acid hydrolases such as non-specific esterase and acid phosphatase is higher in the Purkinje fibers of both the bovine and porcine heart.
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PMID:Enzyme histochemical studies on the Purkinje fibers of the atrioventricular system of the bovine and porcine hearts. 66 82

The oxidation of an optimal concentration of palmitoyl-carnitine, buffered with bovine serum albumin, by isolated rat heart mitochondria was found to give rise to an inactivation of pyruvate dehydrogenase, provided that the concentration of pyruvate present in the mitochondrial incubation was less than 250 muM. The greatest degree of inactivation was found at the lowest pyruvate concentration used, 50 muM, and this concentration was adopted for further studies in which the rate of mitochondrial respiration was varied. This was done by varying the activity of added hexokinase, in the presence of ATP, MgCl2, and glucose, and thus the availability of ADP to the mitochondrion. The pyruvate concentration in the incubation was approximately stabilized by adding pyruvate on the basis of oxygen consumption, with the ratio of pyruvate consumed:O2 consumed determined by trial and error. This device allowed the maintenance of essentially steady pyruvate concentrations and ATP/ADP ratios for at least 5 min, and allowed the pyruvate dehydrogenase interconversion time to approach a steady state. Activities of pyruvate dehydrogenase after 5 or 6 min of respiration were as follows, with values given in nanomoles/min/mg of protein for incubations containing pyruvate as sole substrate, and values for incubations containing pyruvate plus palmitoylcarnitine given in parentheses: State 4, 27 (9); 55% of State 3, 54 (14); 85% of State 3, 73 (28); State 3, 90 (93). Respiratory states are defined by Chance and Williams (1955) J. Biol. Chem. 217, 409-427). Values at earlier time points are also presented so that some idea may be formed of the time course of pyruvate dehydrogenase inactivation. CoASH/acetyl-CoA, NAD+/NADH, and ATP/ADP ratios were measured at the same time points in precisely scaled up incubations. The presence of palmitoylcarnitine in State 4 was found to give essentially no change in NAD+/NADH and ATP/ADP ratios and thus the inactivation of pyruvate dehydrogenase in that state may be attributed to a decreased CoASH/acetyl-CoA ratio. At a respiratory rate of 85% of State 3, palmitoylcarnitine did not change the ATP/ADP ratio, but lowered both CoASH/acetyl-CoA and NAD+/NADH ratios, both of which may contribute to pyruvate dehydrogenase inactivation. In State 3 there was no pyruvate dehydrogenase inactivation, despite a lowered CoASH/acetyl-CoA ratio in the presence of palmitoylcarnitine. It is concluded that ATP/ADP ratio has a pronounced effect on the interconversion of active and inactive pyruvate dehydrogenase, in according with previous work. Moreover, at a given ATP/ADP ratio, the effects of palmitoylcarnitine oxidation on enzyme interconversion are consistent with a mechanism involving the modulation of the interconversion by NAD+/NADH and CoASH/acetyl-CoA ratios...
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PMID:Studies on inactivation of pyruvate dehydrogenase by palmitoylcarnitine oxidation in isolated rat heart mitochondria. 83 28

Changes in the metabolism of Crithidia fasciculata ATCC 11745 when grown in the presence of ethidium bromide were studied. Ethidium bromide-grown cells had decreased respiratory activity as measured by oxygen consumption. More than 50% of the organisms cultivated in a defined medium containing 1.0 mg/liter of ethidium bromide became dyskinetoplastic and had decreased activities of particulate succinate and NADH-linked dehydrogenases as well as of soluble isocitrate dehydrogenase. These cells also had increased activities of particulate alpha-glycerophosphate dehydrogenase, soluble alpha-glycerophosphate dehydrogenase, malic enzyme, hexokinase, and malate dehydrogenase. Ethidium bromide-grown cells had a lower level of ATP and contained less DNA than cells grown in its absence.
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PMID:Effect of ethidium bromide on the oxidative metabolism and enzyme profiles of Crithidia fasciculata. 86 23

Factors which influence the distribution of pyruvate dehydrogenase between its active, unphosphorylated form (PDHa) and its inactive, phosphorylated form (PDHb) have been examined in isolated rat liver mitochondria. A rapid freezing method was developed for the extraction of pyruvate dehydrogenase from incubated mitochondria which prevented interconversions between PHDa and PDHb which normally occur when mitochondria are collected by centrifugal methods. The intramitochondrial ATP:ADP ration was varied over a 100-fold range by the addition of dinitrophenol, oligomycin, or both substances to mitochondria oxidizing 2-oxoglutarate. PDHa activity was found to be inversely proportional to the intramitochondrial ATP:ADP ratio but was not closely correlated with the extramitochondrial adenine nucleotide levels. When mitochondria were incubated in State 4 with succinate and rotenone, the addition of pyruvate increased PDHa activity more than 10-fold without appreciably altering the mitochondrial ATP:ADP ratio. These observations are most readily explained by the known inhibitory effects of pyruvate and ADP on PDHa kinase. PDHa activity could be maintained at a high level by incubating mitochondria in a condition resembling State 3 by the addition of succinate, glucose, and hexokinase. The further addition of octanoate reduced PDHa activity by 60% without appreciably altering the ATP:ADP ratio. Rotenone had a sililar effect. When added in the presence of octanoate, rotenone further decreased PDHa activity whereas 4-pentenoate led to an increase in activity. The effects of octanoate on PDHa activity were not seen when mitochondria were incubated in the presence of high levels of pyruvate, though pyruvate oxidation was till diminished by over 50%. The data suggest that octanoate addition favors the PDHa kinase reaction leading to inactivation of PDHa, and in addition causes the accumulation of NADH and acetyl-CoA which are recognized competitive inhibitors of pyruvate dehydrogenase.
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PMID:Regulation of pyruvate dehydrogenase in isolated rat liver mitochondria. Effects of octanoate, oxidation-reduction state, and adenosine triphosphate to adenosine diphosphate ratio. 111 96

The concentration of 2,3-diphosphoglycerate, and the activities of the enzymes hexokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glutathione reductase and NADH-dependent methaemoglobin reductase in the erythrocytes of newborn and adult sheep were investigated. All the enzyme activities and the concentration of 2,3-diaphosphoglycerate were found to be significantly greater in the erythrocytes of newborn lambs than in those of adult sheep.
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PMID:Postnatal changes in the levels of 2,3-diaphosphoglycerate, reduced glutathione and some enzyme activities in the erythrocytes of lambs. 126 64

1. NADPH-specific mitochondrial enoyl-CoA reductase can be assayed by a sensitive radioactive test, employing tritium-labelled NADPH, synthesized in a prefixed reaction from D-[1-3H]-glucose via the hexokinase and glucose-6-phosphate dehydrogenase reactions. 2. Liver, kidney cortex, heart muscle, skeletal muscle, brown adipose tissue, brain cortex, and aortic intimal tissue are investigated concerning chain lengths specificity of the chain elongation and the enoyl-CoA reductase. Medium-chain acyl-CoA compounds prove to be the best primers for the chain elongation. Enoyl-CoA reductases still show large incorporation rates with hexadecenoyl-CoA. 3. The differences in the chain lengths specificity of the chain elongation and enoyl-CoA reductase can be explained by the inhibitory effect of long-chain acyl-CoA derivatives on the 3-hydroxyacyl-CoA dehydrogenase. 4. The nucleotide specificity in the different tissues reveals two types of chain elongation: In addition to liver and kidney cortex, mitochondria of brown adipose tissue need NADH + NADPH for optimal chain elongation, whereas heart muscle, skeletal muscle and aortic intimal mitochondria only need NADH. 5. Different physiological roles are proposed for the two types. The "heart type" may be of importance in the conservation of reducing equivalents or acetate units in the anaerobic state, the "liver type" may play a role in the transfer of hydrogen from NADPH to the respiratory chain. In addition, the mitochondrial chain elongation may serve as bypass of the first part of the respiratory chain.
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PMID:On the mechanism of malonyl-CoA-independent fatty-acid synthesis. Different properties of the mitochondrial chain elongation and enoylCoA reductase in various tissues. 127 59

A highly sensitive FIA system for chemiluminometric determination of reduced coenzyme, NADH, was developed, using immobilized NADH oxidase from Brevibacterium ammoniagenes. The enzyme catalyzed the oxidation of NADH generating hydrogen peroxide which emitted chemiluminescence when mixed with luminol and potassium ferricyanide. The immobilized enzyme reactor was a mini-column, measuring 1 or 2 mm in inner diameter and 20 mm in length, and the sample volume was only 1 microliter per assay, with a feeding speed of one sample per min and a lowest detection limit of 10 pmol NADH. A FIA system was also developed for the determination of magnesium in human serum, using an enzyme column reactor with simultaneously coimmobilized hexokinase, D-glucose-6-phosphate dehydrogenase, and NADH oxidase. The performance of the system was as satisfactory as a routine colorimetric assay, but with much higher sensitivity.
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PMID:A flow injection analysis system involving immobilized NADH oxidase in column form for clinical analysis. 136 46

Control over oxidative phosphorylation by purified potato mitochondria was determined using the top-down approach of metabolic control analysis. The control over the respiration rate, phosphorylation rate, proton-leak rate and proton motive force exerted by the respiratory chain, phosphorylation reactions and the proton leak were measured over a range of phosphorylation rates from resting (state 4) to maximal (state 3). These rates were obtained by adding different amounts of hexokinase in the presence of glucose, or different amounts of oligomycin in the presence of ADP. The respiratory substrate was NADH or succinate, both of which feed electrons directly to ubiquinone. The rate of oxygen consumption by the alternative oxidase pathway was negligible with NADH as substrate but was measurable with succinate and was subtracted. Control over the respiration rate in potato mitochondria was predominantly exerted by the respiratory chain at all rates except close to state 4, where control by the proton leak was equally or more important. For oxidation of NADH, the flux control coefficient over the respiration rate exerted by the respiratory chain in state 3 was between 0.8 and 1.0, while in state 4, control over the respiration rate was shared about equally between the chain and the proton leak. The control over the phosphorylation rate was predominantly exerted by the respiratory chain, although at low rates control by the phosphorylation system was also important. For oxidation of NADH, the flux control coefficient over the phosphorylation rate exerted by the respiratory chain in state 3 was 0.8-1.0, while near state 4 the flux control coefficients over the phosphorylation rate were about 0.8 for the phosphorylation system and 0.25 for the chain. Control over the proton leak rate was shared between the respiratory chain and the proton leak; the phosphorylation system had negative control. For oxidation of NADH, the flux control coefficients over the leak rate in state 3 were 1.0 for the leak, 0.4 for the chain and -0.4 for the phosphorylation system, while in state 4 the flux control coefficients over leak rate were about 0.5 for the leak and 0.5 for the chain. Control over the magnitude of the protonmotive force was small, between -0.2 and +0.2, reflecting the way the system operates to keep the protonmotive force fairly constant; the respiratory chain and the phosphorylation system had equal and opposite control and there was very little control by the proton leak except near state 4.
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PMID:Characterisation of the control of respiration in potato tuber mitochondria using the top-down approach of metabolic control analysis. 148 62

During steady-state, the Pi released in the medium is derived from glucose-6-phosphate which continuously regenerates the ATP hydrolyzed. A membrane potential (delta psi) can be built up in submitochondrial particles using glucose-6-phosphate and hexokinase as an ATP-regenerating system. The energy derived from the membrane potential thus formed, can be used to promote the energy-dependent transhydrogenation from NADH to NADP+ and the uphill electron transfer from succinate to NAD+. In spite of the large differences in the energies of hydrolysis of ATP (delta G degrees = -7.0 to -9.0 kcal/mol) and of glucose-6-phosphate (delta G degrees = -2.5 kcal/mol), the same ratio between Pi production and either NADPH or NADH formation were measured regardless of whether millimolar concentrations of ATP or a mixture of ADP, glucose-6-phosphate and hexokinase were used. Rat liver mitochondria were able to accumulate Ca2+ when incubated in a medium containing hexokinase, ADP and glucose-6-phosphate. The different reaction measured with the use of glucose-6-phosphate and hexokinase were inhibited by glucose concentrations varying from 0.2 to 2 mM. Glucose shifts the equilibrium of the reaction towards glucose-6-phosphate formation thus leading to a decrease of the ATP concentration in the medium.
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PMID:Reversal of oxidative phosphorylation in submitochondrial particles using glucose 6-phosphate and hexokinase as an ATP regenerating system. 149 30


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