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)

I have re-examined optimum reaction conditions for measurement of creatine kinase (EC 2.7.3.2). The optimum pH is 6.45, and 2,2-bis(hydroxymethyl)-2,2',2''-nitrotriethanol acetate, 200 mmol/liter, is the buffer of choice. Thioglycerol, 20 mmol/liter, is superior for both in-assay reactivation and for storage stability of sera. Fluoride, 25 mmol/liter, a broad inactivator of adenylate kinase (EC 2.7.4.3), has little effect on creatine kinase and is superior to AMP for adenylate kinase inhibition in the assay of creatine kinase. Magnesium ion, ADP, and buffer concentrations are interdependent and their optima must be determined together. The hexokinase/glucose-6-phosphate dehydrogenase activity ratio should not exceed 1.6. The range of linearity is limited by the glucose-6-phosphate dehydrogenase and NAD+ concentrations. Glucose-6-phosphate dehydrogenase, ADP, and NAD+ are the constituents most likely to result in unacceptable blanks. Creatine kinase is inhibited noncompetitively by anions: acetate and fluoride inhibit slightly, but sulfates, nitrates, and excessive chlorides should be avoided.
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PMID:Creatine kinase: re-examination of optimum reaction conditions. 1 66

The activities of several glycolytic enzymes (hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase) as well as glycerol-1-phosphate dehydrogenase and (Mg2+)ATPase in normal cerebrospinal fluid (CSF) and blood plasma samples, from 12 healthy infants, aged 2-18 months, and in supernatants from brain tissue slices, taken during neurosurgical operations from infants of the same range of age were estimated. The values obtained confirm the high activity of the above enzymes found in animal brains, and indicate an independence of these activities in blood plasma and CSF. The origin of the activities of the investigated enzymes in CSF seems to be mainly, if not, exclusively, from brain tissue. This might be useful for detection of brain tissue damage as was earlier proven with LDH activity in CSF.
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PMID:Some glycolytic enzymes in normal cerebrospinal fluid, brain tissue and blood plasma of infants. 13 54

A systematic study of adenosine triphosphate (ATP)-dependent hexose kinases among microorganisms has been undertaken. Sixteen hexose kinases of five major types were partially purified from 12 microorganisms and characterized with respect to specificity for sugar and nucleotide substrates and Michaelis constants for the sugar substrates. Glucokinase activities that phosphorylate glucose and glucosamine are inhibited by N-acetyl-glucosamine and xylose, were found to be present in the non-sulphur photosynthetic bacteria Rhodospirillum rubrum, the blue-green algae Anacystis montana, and the protists Chlorella pyrenoidosa and Chlamydomonas reinhardtii (green algae), Hypochytrium catenoides (Hypochytridiomycete) and Saprolegnia Iitoralis (Oomycete). The myxobacteria Stigmatella aurantiaca contains a glucokinase activity with a different specificity pattern. Anacystis and Chlorella, besides their glucokinase activities, contain highly specific fructokinases, although that from Anacystis can also phosphorylate fructosamine; fructokinase from Anacystis has a molecular weight of 20 000, and exhibits a sigmoidal saturation curve for ATP when the Mg2+/ATP ratio is 2; this curve is transformed to a Michaelian one when under the same conditions an excess of Mg2+ (5 mM) is added. Saprolegnia however, besides the glucokinase, contains a mannofructokinase activity that phosphorylates mannose (Km 0.06 mM) and fructose (1 mM). On the other hand, hexokinase, a low specificity enzyme, was detected in the protist Allomyces arbuscula (Chytridiomycete) and in fungi Mucor hiemalis and Phycomyces blakesleeanus (Zygomycetes), and Schizophyllum commune (Basidiomycete). Schizophyllum contains a glucomannokinase activity together with hexokinase activity. The pattern of distribution of ATP-dependent hexose kinases among microorganisms seems to parallel that reported for biosynthetic pathways for lysine. The correlation with other biochemical parameters is also considered.
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PMID:Distribution of adenosine 5'-triphosphate (ATP)-dependent hexose kinases in microorganisms. 21 81

Keeping constant cellular magnesium an A 23 187 mediated moderate calcium loading of human red cells causes isoosmotic cell shrinkage, potassium efflux, slight decrease of cellular pH, ATP depletion connected with an increase of AMP, ADP and Pi and enhanced lactic acid formation. The calcium loading and accompanying effects can be abolished by EGTA or by extracellular magnesium, the latter kept more than two orders of magnitude above that of calcium which was 30 micrometer. Inhibition of the (Mg2+ + Ca2+)-dependent ATPase by ruthenium red or lanthanum decreases the calcium stimulated lactic acid formation after a lag phase. However, the ATP depletion proceeds faster and is much more pronounced under these conditions. (Mg+2 + Na+ +K+)-dependent ATPase, hexokinase, phosphofructokinase and cell shrinkage are ruled out, too, as mediators of the ATP depletion. This suggests that an unknown ATP consuming reaction, apparently not being related to the calcium pump, causes the calcium induced ATP depletion.
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PMID:Relations between ion shifting, ATP depletion and lactic acid formation in human red cells during moderate calcium loading using the ionophore A 23187. 33 40

1. The preparation of rat heart mitochondria with Potter-Elvehjem homogenizer results in mitochondria showing stimualtion of respiration induced by Mg2+. This stimualtion is neither caused by adherent hexokinase nor by energy-dependent magnesium accumulation (Mg2+ content in the presence of 10 mM glutamate: 22 nmoles/mg protein; in the presence of glutamate plus antimycin A 21 nmoles/mg protein). 2. The effect of added magnesium is excluded by addition of carboxyatractyloside. This demonstrates the activity of an ATPase outside of the mitochondrial inner membrane. 3. A simple and rapid method for the preparation of Mg2+-insensitive rat heart mitochondria is presented. The minced heart is pressed through a normal syringe and then treated with trypsin. 4. A comparison of mitochondria of both preparations shows that there is no difference in magnesium content and no energy-dependent magnesium influx.
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PMID:Influence of Mg2+-ions on the properties of rat heart mitochondria in dependence on the preparation. 70 27

In a theoretical study the influence of hemoglobin and Mg-ions as binding partners of red cell 2,3-diphosphoglycerate and ATP was investigated. Free hemoglobin may be an efficient competitor of Mg2+ for the ligand ATP. At conditions which favour hemoglobin as binding partner (i.e. desoxygenation, low medium pH and incubation temperature, as in blood preservation) up to 95% of the whole cellular ATP (ca. 2mM in cell water) may be bound to hemoglobin (ca. 7 mM). This binding is largely prevented in the presence of physiological amounts of diphosphoglycerate (ca. 7 mM) which is in excess and has a higher binding affinity to hemoglobin. Therefore, diphosphoglycerate keeps ATP (MgATP) in cell water solution at conditions in which Hb would trop it in the presence of Mg2+ (ca. 3mM). It can be calculated that, by lack of free MgATP, the activity of hexokinase within the cell drops by a factor of greater than 10 when diphosphoglycerate is metabolized. This indirect activation by diphosphoglycerate of hexokinase is operative at free concentrations of DPG far below those which exert the well known excess inhibitory effect on hexokinase and phosphofructokinase. In a model study, the activation by diphosphoglycerate of the initial two-kinase stage was introduced into a simplified kinetic model of glycolysis. A pronounced hysteresis loop of the stationary concentrations of ATP and diphosphoglycerate was produced indicating the existence of several stationary states, one with high ATP and high diphosphoglycerate, the other one with low values. It is demonstrated that diphosphoglycerate, being a protector of glycolysis at physiological concentrations, triggers an autocatalytic breakdown of the energy state when permitted to drop to low values.
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PMID:[Importance of binding of 2,3-diphosphoglycerate and ATP to hemoglobin for erythrocyte glycolysis: activation by 2,3-diphosphoglycerate of hexokinase at intracellular conditions]. 70 29

(1) Ca2+ efflux from rabbit skeletal muscle sarcoplasmic reticulum vesicles pre-loaded with 45Ca2+ was studied in the presence and in the absence of external Ca2+. (2) In the absence of Ca2+ in the assay media, ADP activates the Ca2+ efflux. The increment of Ca2+ efflux requires Pi, is coupled to ATP synthesis, and is inhibited by external Ca2+ (Ki 0.1-0.2 muM). (3) When Ca2+ is added to the assay media, ADP alone activates the Ca2+ efflux, but this is coupled to a Ca2+ influx of the same magnitude. It is therefore an exchange of internal for external Ca2+ in a 1:1 ratio. (4) The ADP-activated Ca2+ exchange requires external Ca2+ with an apparent Km of 0.1-0.2 muM, does not require the addition of Pi or Mg2+, although 3-10 mM MgCl2 activates it. It is not inhibited by the removal of contaminating ATP with hexokinase plus glucose. (5) It seems likely that Ca2+ can be translocated across sarcoplasmic reticulum membrane without the formation of a phosphorylated intermediate.
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PMID:ADP-activated calcium ion exchange in sarcoplasmic reticulum vesicles. 81 33

The Mg2+ precipitation procedure of R. D. Palmiter ((1974) Biochemistry 13, 3606) has been used for preparative scale isolation of polysomes from Ehrlich ascites mitochondria. Digitonin-washed metochondria used for isolating the polysomes contain no detectable reduced nicotinamide adenine dinucleotide phosphate-cytochrome c reductase and over 200-fold reduced hexokinase activity. The mitochondrial polysomes exhibit a heterogeneous sedimentation and appear to contain highly aggregated particlses ranging over hexamers. These polysomes are sensitive to RNase, (ethylenedinitrilo)tetraacetic acid and puromycin. Mitochondrial polysomes are active in portein synthesis when supplied with supernatant enzymes from the homologous mitochondrial source or from Escherichia coli. Cytoplasmic enzymes, however, appear to be completely inactive. Protein synthesis by mitochrondrial polysomes is sensitive to chloramphenicol and resistant to cycloheximide and emetine. The procedure yields particles containing intact rRNAs. The extent of cytoplasmic RNA contaminating the total mitochondrial RNA or mitochondrial polysomal RNA has been estimated to be negligible.
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PMID:Messenger ribonucleic acid metabolism in mammalian mitochondria. Isolation and characterization of polyribosomes from Ehrlich ascites mitochondria. 82 18

It has been found that adenylic nucleotides at physiological concentrations solubilize mitochondrial hexokinase from muscles. The solubilizing effect of ATP is reversible in the presence of Mg2+ ions. It is shown that Mg2+ and glucose induce the transition of isoenzymes I and II of hexokinase from the free state to the bound one. Kinetic parameters of the free and bound forms of hexokinase have been determined. The stability of hexokinase has been found to vary, depending on its localization in the cell. Possible action mechanisms of reagents, exerting solubilizing and binding effects on the enzyme and the physiological role of hexokinase ability to exist in free and bound states are discussed.
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PMID:[Changes in the properties of hexokinase from hyaloplasm on binding with mitochondria]. 91 36

Human erythrocyte hexokinase (EC 2.7.1.1) is inhibited competitively with respect to Mg-ATP2- by uncomplexed Mg2+ (Ki = 16--18 mM) and ATP4- (Ki = 1.6 mM). No real activation by low concentrations of Mg2+ could be detected and no allosteric behaviour was observed under the conditions tested. The temperature dependence of the enzyme was studied in relationship to the presence of Mg2+ or ATP4-. At equal concentrations of Mg2+ and ATP4- a break in the Arrhenius plot was observed at 27.5 degrees C, the higher temperature form of the enzyme having the lower activation energy. This break point in the Arrhenius plot was shifted to 36 degrees C in the presence of 5 mM Mg2+. A straight-line relationship was observed in the presence of 2.5 mM ATP4-. The Km for Mg-ATP2- showed a linear increase at temperatures over about 36 degrees C independent of the presence of Mg2+ or ATP4-. The nature of these phenomena is discussed.
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PMID:Kinetics of human erythrocyte hexokinase. Influence of temperature, ATP4- and magnesium ions. 100 15


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