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)

1. The pentose phosphate pathway in Krebs ascites cells was investigated for regulatory reactions. For comparison, the glycolytic pathway was studied simultaneously. 2. Activities of the pentose phosphate pathway enzymes were low in contrast with those of the enzymes of glycolysis. The K(m) values of glucose 6-phosphate dehydrogenase for both substrate and cofactor were about four times the reported upper limit for the enzyme from normal tissues. Fructose 1,6-diphosphate and NADPH competitively inhibited 6-phosphogluconate dehydrogenase. 3. About 28% of the hexokinase activity was in the particulate fraction of the cells. The soluble enzyme was inhibited by fructose 1,6-diphosphate and ribose 5-phosphate, but not by 3-phosphoglycerate. The behaviour of the partially purified soluble enzyme in vitro in a system simulating the concentrations of ATP, glucose 6-phosphate and P(i) found in vivo is reported. 4. Kinetics of metabolite accumulation during the transient state after the addition of glucose to the cells indicated two phases of glucose phosphorylation, an initial rapid phase followed abruptly by a slow phase extending into the steady state. 5. Of the pentose phosphate pathway intermediates, accumulation of 6-phosphogluconate, sedoheptulose 7-phosphate and fructose 6-phosphate paralleled the accumulation of glucose 6-phosphate. Erythrose 4-phosphate reached the steady-state concentration by 2min., whereas the pentose phosphates accumulated linearly. 6. The mass-action ratios of the pentose phosphate pathway reactions were calculated. The transketolase reaction was at equilibrium by 30sec. and then progressively shifted away from equilibrium towards the steady-state ratio. The glucose 6-phosphate dehydrogenase was far from equilibrium at all times. 7. Investigation of the flux of [(14)C]glucose carbon confirmed the existence of an operative pentose phosphate pathway in ascites cells, contributing 1% of the total flux in control cells and 10% in cells treated with phenazine methosulphate. 8. The pentose phosphate formed by way of the direct oxidative route and estimated from the (14)CO(2) yields represented 20% of the total accumulated pentose phosphate, the other 80% being formed by the non-oxidative reactions of the pentose phosphate pathway. 9. The pentose phosphate pathway appears to function as two separate pathways, both operating towards pentose phosphate formation. Control of the two pathways is discussed.
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PMID:The pentose phosphate pathway of glucose metabolism. Enzyme profiles and transient and steady-state content of intermediates of alternative pathways of glucose metabolism in Krebs ascites cells. 536 Jun 73

Cells of the aerotolerant anaerobe Giardia lamblia respire in the presence of oxygen. Endogenous respiration is stimulated by glucose but not by other carbohydrates and Krebs cycle intermediates. Endogenous and glucose-stimulated respiration are insensitive to cyanide, malonate, and 2,4-dinitrophenol, but are inhibited by atabrin and iodoacetamide. G. lamblia produces ethanol, acetate and CO2 both aerobically and anaerobically either from endogenous reserves or exogenous glucose. Molecular hydrogen is not produced. The following enzyme activities were detected in homogenates: hexokinase, fructose-biphosphate aldolase, pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, malate dehydrogenase (decarboxylating), pyruvate synthase, acetyl-CoA synthetase, alcohol dehydrogenase (NADP+), NADH dehydrogenase, NADPH dehydrogenase, NADPH oxidoreductase and superoxide dismutase. The enzymes of energy and carbohydrate metabolism are nonsedimentable (109 000 x g for 30 min). Activities of lactate dehydrogenase, hydrogenase, phosphate acetyltransferase, acetate kinase, citrate synthase, succinate dehydrogenase, fumarate hydratase and catalase were below the limits of detection. The results suggest the occurrence of glycolysis, energy production by substrate level phosphorylation and a flavin, iron-sulfur protein mediated electron transport system as well as the absence of cytochrome mediated oxidative phosphorylation and functional Krebs cycle.
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PMID:Energy metabolism of the anaerobic protozoon Giardia lamblia. 610 7

The quantitative assay of hexokinase (HK), phosphorylase, phosphofructokinase (PFK), glucose 6-phosphate dehydrogenase (G-6-PDH), glycerol 3-phosphate dehydrogenase (G-3 PDH) and lactate dehydrogenase (LDH) revealed that coxal muscles compared to hepatopancreas contained higher activities of all the enzymes investigated. It appears that the coxal muscles of the premolt field crab has carbohydrate-based fuel economy. The hepatopancreas is a rich source of lipid and very poor source of glycogen. The activity of G-6-PDH is moderately high in the hepatopancreas. It seems that in this lipogenic tissue conversion of G-6-P to triose phosphate occurs predominately via pentose-phosphate pathway thus generating NADPH for lipogenesis. The relative G-3PDH ad LDH activities in hepatopancreas and coxal muscles led us to believe that the reconversion of NAD from NADH in hepatopancreas nd muscle flexor is effected by glycerol 3-phosphate shuttle, whereas in muscle extensor it is achieved by both G-3PDH and LDH activities.
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PMID:Glycolytic enzymes in the premolt field crab Paratelphusa hydrodromus (Milne-Edwards) (Crustacea). 619 88

A pathway from glucose via sorbitol bypasses the control points of hexokinase and phosphofructokinase in glucose metabolism. It also may produce glycerol, linking the bypass to lipid synthesis. Utilization of this bypass is favored by a plentiful supply of glucose--hence, conditions under which glycolysis also is active. The bypass further involves oxidation of NADPH, so the pentose phosphate pathway and the bypass are mutually facilitative. Possible consequences in different organs under normal and pathological, especially diabetic, conditions are detailed. Enzymes with related structures (for example, sorbitol dehydrogenase and alcohol dehydrogenase, and possibly, aldehyde reductase and aldose reductase, respectively) are linked functionally by this scheme. Some enzymes of the bypass also feature in glycolysis (aldolase and alcohol dehydrogenase), and these enzymes, with the reductases involved, are proteins known to occur in different classes or multiple isozyme forms. Two of the enzymes (aldolase and alcohol dehydrogenase) both involve classes with and without a catalytic metal (zinc). The existence of parallel pathways and the occurrence of similar enzymic steps in one pathway may help to explain the abundance and multiplicity of enzymes such as reductases, aldolases, and alcohol dehydrogenases.
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PMID:Enzyme relationships in a sorbitol pathway that bypasses glycolysis and pentose phosphates in glucose metabolism. 640 81

A BASIC computer program has been developed which has been used to show that bovine lens aldose reductase with NADPH as substrate follows a 1:1 function, while rabbit lens hexokinase has a rate equation of minimum degree 2:2, and bovine lens polyol dehydrogenase has a rate equation of minimum degree 1:2 with xylitol as substrate. The parameter estimates obtained are very close to those from the BMDP3R curvefitting program on an ICL 2980 mainframe computer, with identical conclusions as to the minimum degree of the rate equation. The computer program can be run on any microcomputer with high resolution graphics in less than 48 K of random access memory.
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PMID:Microcomputer analysis of hyperbolic and non-hyperbolic steady-state kinetics. 643 8

The role of mitochondrial hexokinase (EC 2.7.1.1.) and mitochondrial ATP synthesis in the utilization of glucose for the support of estrogen biosynthesis was examined in placental mitochondrial preparations supplemented with NADP+, glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 4-androstene-3,17-dione. With 14 mitochondrial preparations, rates of steroid aromatization supported by 100 mM glucose and 20 mM ATP had a mean of 65.7 +/- 7.1 (SD) % of rates achieved with saturating levels of glucose 6-phosphate. ADP, but not AMP, could substitute for ATP in this system. Aromatization supported by glucose and high concentrations of ADP was inhibited by AMP but not by 2,4-dinitrophenol or oligomycin. Glucose also supported mitochondrial aromatization when combined with a respiratory chain-linked metabolic substrate (glycerol 3-phosphate) and a limiting concentration of ADP (2 mM). This support was inhibited by 2,4-dinitrophenol, the p-trifluoromethoxyphenylhydrazone of carbonyl cyanide, oligomycin and atractyloside. Thus, glucose metabolism by mitochondrial hexokinase, utilizing ATP generated either by oxidative phosphorylation or mitochondrial adenylate kinase (EC 2.7.4.3), can be coupled with a soluble NADPH-generating system to provide effective support of mitochondrial estrogen synthesis.
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PMID:The support of steroid aromatization by mitochondrial metabolic activities of the human placenta. 670 59

Subcellular distribution of hexokinase (HK) isoenzymes in 22 human breast cancers (21 primary cancers and 1 axillary metastatic growth) and 7 non-pathological human mammary gland tissue samples was studied with starch gel electrophoresis on isolated cell fractions obtained by differential centrifugation. Fractions used were cytosol, mitochondria and microsomes. A comparison of two methods for detecting HK activity was made, yielding different results regarding HK II and HK III. A method based on the ability of NADPH to fluoresce in UV gave a constant pattern of HK isoenzymes. In non-pathological breast tissue, only HK I was seen, i.e. in the cytosol and the microsomal fractions. HK I was also seen in all fractions of the cancers, but another more anodal band of HK I, as well as HK II and HK III, consistently appeared in the cytosol fractions. The more commonly used staining technique with tetrazolium dye revealed HK II in 45% and HK III in 50% of the samples. The pattern of HK isoenzymes in the cancers was the same irrespective of estrogen and progesterone cytosolic receptor contents and the histology of the tumors. The fluorescence method is, therefore, much more sensitive than the tetrazolium technique for detecting HK activity after electrophoresis and could explain difference in results obtained by various laboratories.
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PMID:Isoenzyme pattern and subcellular localization of hexokinases in human breast cancer and nonpathological breast tissue. 674 20

The sorbitol pathway in human lenses is evaluated on the enzymic level. Adult lenses, normal and nondiabetic as well as diabetic cataracts, are found to contain limited levels of aldose reductase (AR) and high levels of polyol dehydrogenase (PD) relative to the animal lens. AR is confined primarily to the lens epithelium and is two to three times higher in juvenile lenses than in the adult lens. The level of AR in the epithelium of juvenile lenses is sufficient to cause significant osmotic stress. The Km of glucose of AR is roughly 200 mM, whereas the Km for NADPH is 0.06 mM. NADP inhibits human lens AR noncompetitively and has a Ki equivalent to the Km for NADPH. PD occurs in both the lens epithelium and cortex, remains persistently high with age, and decreases with increased cortical involvement. The Km of sorbitol for PD is 1.4 mM and for NAD is 0.06 mM. NADH (Ki 0.002 mM) competitively inhibits PD in the forward direction. PD purified 100-fold from diabetic and nondiabetic cataracts and normal lenses exhibit similar kinetic constants. PD has an extremely high Vmax in the fructose-to-sorbitol direction. The Km of fructose is 40 mM and for NADH is 0.02 mM. At high enough concentration, alrestatin also inhibits PD. The added activities of AR and PD in producing sorbitol and fructose in combination with decreased hexokinase with age may account for diabetic cataract formation in human lenses exposed to a high glucose stress. Nucleotide levels are reported for senile cataractous lenses.
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PMID:The sorbitol pathway in the human lens: aldose reductase and polyol dehydrogenase. 678 33

The mannitol cycle is an important NADPH regenerating system in Alternaria alternata. The cycle is built up to the following enzymes: mannitol 1-phosphate dehydrogenase, mannitol 1-phosphatase, mannitol dehydrogenase and hexokinase. The net reaction of one cycle turn is: NADH + NADP+ + ATP leads to NAD+ + NADPH + ADP + Pi. The enzymes needed for an operating cycle were found in Aspergillus, Botrytis, Penicillium, Pyricularia, Trichothecium, Cladosporium and Thermomyces all genera belonging to Fungi Imperfecti. The only genus of this class lacking the cycle was Candida. No genera from the classes Basidiomycetes and Phycomycetes showed any mannitol 1-phosphate dehydrogenase or mannitol 1-phosphatase activities. The genera investigated, belonging to Ascomycetes, Gibberella, Ceratocystis and Neurospora all lacked mannitol 1-phosphate dehydrogenase. It was concluded that the mannitol cycle is an important and widespread pathway for NADH oxidation and NADP+ reduction in the organisms belonging to the class Fungi Imperfecti.
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PMID:The distribution of the NADPH regenerating mannitol cycle among fungal species. 678 99

A simple fluorimetric assay for the determination of carbamoyl phosphate in tissue extracts is described. In the assay, production of ATP from carbamoyl phosphate and ADP by carbamate kinase is coupled to the formation of NADPH, using glucose, hexokinase, NADP+, and glucose-6-phosphate dehydrogenase. Production of NADPH in this system proved to be equal to the amount of carbamoyl phosphate present.
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PMID:Fluorimetric determination of carbamoyl phosphate. 685 36


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