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

---

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

Titrations of the tryptophan fluorescence of yeast hexokinase (ATP:D-hexose 6-phosphortransferase, EC 2.7.1.1.) isozymes P-I (A) and P-II (B) were performed with Mg2+, Li+, Na+ and K+ as titrant in absence and in presence of glucose, and vice versa, at pH 8.3 and 5.5 at 20 degrees C. Mg2+ quenches the fluorescence of surface tryptophan primarily and does so by producing a conformational change which alters the microenvironment of the tryptophan. For both isozymes Mg2+ exerts a specific ion effect, i.e. significantly larger than the ionic strength (I) effect, which enhances the glucose quenching by causing a conformation change which increases the glucose-binding constant. For the P-I isozyme glucose binding exhibits positive cooperativity at both pH 8.3 and 5.5 when the ionic strength (I) is low, i.e. significantly larger than the ionic strength (I) effect, which enhances the glucose quenching by causing a conformation change which increases the glucose-binding constant. For the P-I isozyme glucose binding exhibits positive sooperativity at both pH 8.3 and 5.5 when the ionic strength (I) is low, i.e. 0.04 or less, regardless of which of the above four cations is present. For P-II, however, glucose binding is non-cooperative at pH 8.3 regardless of I or the cation species and at pH 5.5 and low I with K+ or Mg2+ as the predominant cation present, but there is apparent negative cooperativity at pH 5.5 and low I when Na+ or Li+ predominates. These results are discussed in terms of known structural characteristics of the isozymes.
...
PMID:Effects of free magnesium and alkali ions on the conformation and glucose-binding strength of yeast hexokinase isozymes. 698

To probe the effects of the substrate, glucose, and the cofactor, Mg2+, on the structure of hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1), titrations of the tryptophan fluorescence of yeast hexokinase isozyme P-II(B) were performed. Acrylamide was used as a quenching titrant in the absence and in the presence of glucose and Mg2+ singly and together at pH 5.5 and 8.3 at 20 degrees C. The four tryptophan residues of the monomeric subunit of yeast hexokinase may be classified as two surface residues, one being highly accessible to dissolved I- and one with restricted accessibility to I-, one glucose-quenchable residue in the cleft, and one buried (Kramp, D.C. and Feldman, I. (1978) Biochim. Biophys. Acta 537, 406--416). The acrylamide data were analyzed by least-squares computer analysis for quenching constants and fractional fluorescence values of the tryptophan residues. The quenching constants measure the accessibilities of the residues to the quencher, while the fractional fluorescences are related to the microenvironments of the fluorophores. At each pH value, glucose altered the quenching constants, but not the fractional fluorescence, of the tryptophan residues. Mg2+ greatly accentuated at this glucose effect, especially for the surface residue near the cleft opening. Comparison of acrylamide- and I-quenching data shows that this particular residue has a positively charged microenvironment. A pH change from 5.5 to 8.3 increased the acylamide-accessibility of the cleft tryptophan but did not seem to influence accessibility of the surface residues or the buried residue significantly, thus strengthening our previous conclusion that the cleft opening is small enough at pH 5.5 to partially restrict entrance of organic molecules and negative ions. However, with saturating glucose present there was a pH effect on the surface residue accessibility. Titrations in 55 vol.% glycerol suggest the presence of transient channels (not just holes) in the hexokinase structure, which allows penetration of the protein by solution. Consequently, the buried tryptophan residue is quenched more strongly by dissolved acrylamide than is attributable to diffusion of quencher through the protein matrix.
...
PMID:Effects of glucose and magnesium ion on the quenching of yeast hexokinase fluorescence by acrylamide. 700 Jan 90

ATP was synthesized in presence of insulin or insulin and prostaglandin E2 by rat skeletal muscle particulate preparation enriched in plasmatic membranes. Isolation of the ATP was carried out using column chromatography on Dowex 1 x 8/cl-form, 100--200 mesh). ATP was formed within 1 min in a medium containing Tris-HCl buffer, pH 7.5, ADP, Mg2+, inorganic phosphate, NaF during NADH-related oxidation involving cytochrome c and O2 in amounts of 100--300 pmoles per mg of protein. Quantitative estimation of ATP in the lyophilized product was carried out by means of spectrophotometry at 340 nm of NADPH formed during a coupled enzymatic reactions involving hexokinase and glycose-6-phosphate dehydrogenase. This products identified by descending paper chromatography on Whatman NI in the system containing ethanol-ammonium citrate pH 4.4 and pH 7.5. Identification of ATP was also performed by thin-layer chromatography. The product was tested for content of ribose (orcinol method) and of inorganic phosphate after acid hydrolysis within 7.5 min at 100 degrees. In the product obtained adenine was identified by UV-spectrophotometry at 260 nm. A salt of ATP was synthesized from the product obtained.
...
PMID:[Isolation, identification and quantitative determination of the ATP synthesized by a preparation of plasma membrane-enriched particles from rat skeletal muscles in the presence of insulin]. 703 65

1. A number of reactive triazine dyes specifically and irreversibly inactive yeast hexokinase at pH 8.5 and 33 degrees C. Under these conditions, the enzyme is readily inactivated by 100 microM-Procion Green H-4G, Blue H-B, Turquoise H-7G and Turquoise H-A, is less readily inactivated by Procion Brown H-2G. Green HE-4BD, Red HE-3B and Yellow H-5G and is not inactivated at all by Procion Yellow H-A. 2. The inactivation of hexokinase by Procion Green H-4G is competitively inhibited by the adenine nucleotides ATP and ADP and the sugar substrates D-glucose, D-mannose and D-fructose but not by nonsubstrates such as D-arabinose and D-galactose. 3. Quantitatively inhibited hexokinase contains approx. 1 mol of dye per mol of monomer of mol.wt. 51000. The inhibition is irreversible and activity cannot be recovered on incubation with high concentration (20 mM) of ATP or D-glucose. 4. Mg2+ protects the enzyme against inactivation by Procion Green H-4G but enhances the rate of inactivation by all the other Procion dyes tested. In the presence of 10 mM-Mg2+ the apparent dissociation constant between enzyme and dye is reduced from 199.0 microM to 41.6 microM. Binding of the dye to hexokinase is accompanied by characteristic spectral changes in the range 560-700 nm. 5. Mg2+ promotes binding of yeast hexokinase to agarose-immobilized Procion Green H-4G but not to the other dyes tested. Elution could be effected by omission of Mg2+ from the column irrigants or by inclusion of MgATP or D-glucose, but not by D-galactose. These effects can be exploited to purify hexokinase from crude yeast extracts. 6. The specific active-site-directed binding of triazine dyes to yeast hexokinase is interpreted in terms of the crystallographic structure of the hexokinase monomer.
...
PMID:The interaction of yeast hexokinase with Procion Green H-4G. 703 16

The conditions of reversible transition of hexokinase from the hyaloplasm to the rat skeletal muscle microsomal membranes were studied. The maximal absorption of the enzyme by the membranes was observed in the presence of Mg2+ and glucose at weakly alkaline values of pH. Adenyl nucleotides and glucose 6-phosphate taken at physiological concentrations at neutral and weakly acid values of pH make the effect of Mg2+ reversible. It was shown that the both hexokinase isozymes I and II localized in muscle hyaloplasm are capable of reversible transition from the free state to the bound one. All the effects observed during hexokinase interaction with the rough microsomal fraction occurred in the cases of a purified muscle sarcoplasmic reticulum fraction. The conditions for the enzyme interaction with the microsomal and mitochondrial membrane fractions were found to be practically identical. However, when the enzyme was bound to the microsomal membrane, some reversible changes (e. g. increase of V) took place; the Km value for glucose remained thereby unchanged. The data obtained are discussed in terms of an adsorption mechanism of hexokinase activity control in the cell.
...
PMID:[Interaction of isozymes I and II of hexokinase with a microsomal fraction of skeletal muscle of rats]. 712 97

The S-methylated derivatives of adenosine 5'-O-(1-thiotriphosphate) (ATP alpha SCH3) have been prepared by the reaction of both diastereomers of adenosine 5'-O-(1-thiotriphosphate) (ATP alpha S) with methyl iodide. At physiological pH ATP alpha SCH3 was unstable, decomposing predominantly to adenosine 5'-O-(S-methyl thiophosphate) (AMPSCH3) and pyrophosphate. A minor degradation pathway also yielded ATP and methyl mercaptan. Greatly enhanced stability was observed at lower pH. The Sp diastereomer of ATP alpha SCH3 was a substrate for hexokinase and acetate kinase, and both diastereomers were active with fructose-6-phosphate kinase. The products of these reactions were the appropriate sugar or acyl phosphate, AMPSCH3, and inorganic phosphate, the latter two species arising from the breakdown of the transient intermediate 5'-O-(S-methyl 1-thiodiphosphate) (ADP alpha SCH3). No measurable substrate activities were observed with creatine and phosphoglycerate kinase. These results are interpreted as meaning that creatine and phosphoglycerate kinase require Mg2+ coordination to the alpha-phosphate group during the enzyme-catalyzed reaction whereas the other three enzymes do not. Attempts to prepare adenosine 5'-O-(S-methyl 2-thiotriphosphate) (ATP beta SCH3) and ADP-alpha SCH3 by similar methods were unsuccessful with adenosine 5'-O-(S-methyl 2-thiodiphosphate) (ADP beta S) and AMPSCH3 being respectively isolated as the major products.
...
PMID:S-Methylated nucleoside phosphorothioates as probes of enzyme metal X nucleotide binding sites. 715 May 48

Progesterone decreases the oxidation of 2-deoxyglucose and glucose through the pentose-phosphate pathway in isolated female rat adipocytes and, therefore, the effect of this steroid incubation in vitro, progesterone decreased total hexokinase activity but did not affect the isoenzyme-I activity. Progesterone had no direct effect on fat cell cytosol hexokinase and its action on glucose oxidation was not affected by variations in the concentration of Mg2+, the cofactor of hexokinase. Our data suggest that the decreased activity of hexokinase in the presence of progesterone is due to a decrease in the activity of the insulin-sensitive isoenzyme-II. This results from the steroid acting at a step beyond enzyme activation and may be mediated by a feedback mechanism.
...
PMID:Progesterone and glucose metabolism in the female rat adipocyte: effect on hexokinase activity. 717 24

Hexokinase from rat skeletal muscle hyaloplasm is represented by two isozymic forms I and II. The values of apparent Km (glucose) for these forms were calculated according to the Reiner method. After binding to mitochondrial membranes under effects of Mg2+ the value of V for hexokinase isozyme II is increased 3-fold, while its Km value is decreased 5 times; the properties of isozyme I remain thereby unchanged. After cessation of interaction with the membrane, under effect of ATP the free hexokinase reveals the same kinetic properties (V, Km, sensitivity to the inhibiting effect of glucose 6-phosphate) as does the native enzyme from hyaloplasm. The ability of hexokinase to exist in a bound or free state is also reversible and depends on the Mg2+/ATP ratio. The conditions for a reversible transfer of muscle hexokinase (isozymes I and II) from the hyaloplasm to the mitochondria-bound state completely coincide with those for cardiac enzyme (isozyme I). The data obtained are discussed in terms of a concept on an adsorption mechanism controlling the enzyme activity.
...
PMID:[Kinetics behavior of isozymes I and II of rat skeletal muscle hexokinase after their binding to mitochondrial membranes]. 728 81

The atractyloside-insensitive accumulation of adenine nucleotides by rat liver mitochondria (as opposed to the exchange-diffusion catalysed by the adenine nucleotide translocase) has been measured by using the luciferin/luciferase assay as well as by measuring [14C]ATP uptake. In foetal rat liver mitochondria ATP is accumulated more rapidly than ADP, whereas AMP is not taken up. The uptake of ATP occurs against a concentration gradient, and the rate of ATP uptake is greater in foetal than in adult rat liver mitochondria. The accumulated [14C]ATP is shown to be present within the mitochondrial matrix space and is freely available to the adenine nucleotide translocase for exchange with ATP present in the external medium. The uptake is specific for ATP and ADP and is not inhibited by adenosine 5'-[beta gamma-imido] triphosphate, GTP, CTP, cyclic AMP or Pi, whereas dATP and AMP do inhibit ATP accumulation. The ATP accumulation is also inhibited by carbonyl cyanide m-chlorophenylhydrazone, KCN and mersalyl but is insensitive to atractyloside. The ATP uptake is concentration-dependent and exhibits Michaelis-Menten kinetics. The divalent cations Mg2+ and Ca2+ greatly enhance ATP accumulation, and the presence of hexokinase inhibits the uptake of ATP by foetal rat liver mitochondria. These latter effects provide an explanation for the low adenine nucleotide content of foetal rat liver mitochondria and the rapid increase that occurs in the mitochondrial adenine nucleotide concentration in vivo immediately after birth.
...
PMID:The transport and accumulation of adenine nucleotides during mitochondrial biogenesis. 730 14

A general kinetic method is described for determining the dissociation constants of metal-ATP complexes that act as inhibitory substrate analogues for any enzyme that utilizes MgATP(2-). The usefulness of the procedure is illustrated by the results obtained from studies of the inhibition of hexokinase by lanthanide-ATP (LnATP) complexes. At relatively low concentrations of Mg2+, these complexes act as linear competitive inhibitors with respect to MgATP(2-). In the presence of higher, fixed concentrations of Mg2+, however, double reciprocal plots of the inhibition by LnATP vs. MgATP are nonlinear, and the data can be used to determine the ratio of the dissociation constants for the LnATP and MgATP complexes. As values are available for the dissociation constant of MgATP under a variety of conditions, that for any LnATP complex can be calculated. The dissociation constant for EuATP at pH 8.0 is 0.16 microM, while that for GdATP is 0.91 microM at pH 6.0, 0.087 microM at pH 7.95, and 1 microM at pH 8.65. Between pH 6 and 8, the ratio of the dissociation constants for GdATP and MgATP(2-) remains constant, and thus, within this range of pH, the lanthanide species involved must be Gd3+ and GdATP-. The method can also be applied to the determination of dissociation constants for inhibitory metal-ADP complexes if MgADP- is used as the variable substrate.
...
PMID:A kinetic method for determining dissociation constants for metal complexes of adenosine 5'-triphosphate and adenosine 5'-diphosphate. 740 34


<< Previous 1 2 3 4 5 6 7 8 9 Next >>

---