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:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Michaelis constants for MgATP with yeast hexokinase vary from 28 microM with D-mannose to above 4 mM for the slow ATPase reaction, with the different values reflecting the degree of synergism in binding of MgATP and the sugar substrate. The best substrates show the greatest synergism, but the correlation is not exact. Similar synergistic binding between MgADP or its methylene analogue and phosphorylated sugars is seen. Product inhibiton of MgADP vs. MgATP and vice versa appears noncompetitive at low levels of variable substrate but becomes competitive at high levels. These patterns show that MgATP can combine with E-glucose-6-P (Ki = 4 mM) and MgADP with E-glucose (Ki = 1.6 mM). Isotope partitioning studies with glucose or glucose-6-P have determined the rates of release of these substrates from binary and ternary complexes and, together with reverse isotope exchange studies and the product inhibition studies mentioned above, have shown that the kinetic mechanism is a somewhat random one in which dissociation of sugars from productive ternary complexes is very slow, but release from nonproductive ternary complexes occurs at rates similar to those from binary enzyme-sugar complexes. D-Arabinose-5-P has a Km of 4.6 mM and a Vmax 5% that for glucose-6-P, confirming that the high Km for D-arabinose in the forward direction is caused by the low proportion in the furanose form. The dissociation constant of MgADP in the absence of sugars was determined from the Ki of 5.8 mM for MgADP as a competitive inhibitor vs. MgATP of the slow ATPase reaction.
...
PMID:Substrate synergism and the kinetic mechanism of yeast hexokinase. 704 74

Yeast cells can respond and adapt to osmotic stress. In our attempt to clarify the molecular mechanisms of cellular responses to osmotic stress, we cloned seven cDNAs for hyperosmolarity-responsive (HOR) genes from Saccharomyces cerevisiae by a differential screening method. Structural analysis of the clones revealed that those designated HOR1, HOR3, HOR4, HOR5 and HOR6 encoded glycerol-3-phosphate dehydrogenase (Gpd1p), glucokinase (Glk1p), hexose transporter (Hxt1p), heat-shock protein 12 (Hsp12p) and Na+, K+, Li(+)-ATPase (Ena1p), respectively. HOR2 and HOR7 corresponded to novel genes. Gpd1p is a key enzyme in the synthesis of glycerol, which is a major osmoprotectant in S. cerevisiae. Cloning of HOR1/GPD1 as a HOR gene indicates that the accumulation of glycerol in yeast cells under hyperosmotic stress is, at least in part, caused by an increase in the level of GPDH protein. We performed a series of Northern blot analyses using HOR cDNAs as probes and RNAs prepared from cells grown under various conditions and from various mutant cells. The results suggested that all the HOR genes are regulated by common signal transduction pathways. However, the fact that they exhibited certain distinct responses indicated that they might also be regulated by specific pathways in addition to the common pathways. Ca2+ seemed to be involved in the signaling systems. In addition, Hog1p, one of the MAP kinases in yeast, appeared to be involved in the regulation of expression of HOR genes, although its function seemed to be insufficient for the overall regulation of expression of these genes.
...
PMID:Cloning and characterization of seven cDNAs for hyperosmolarity-responsive (HOR) genes of Saccharomyces cerevisiae. 750 Sep 33

Copper(II) complexes were encapsulated in human red blood cells in order to test their possible use as antioxidant drugs by virtue of their labile character. ESR spectroscopy was used to verify whether encapsulation in red blood cells leads to the modification of such complexes. With copper(II) complexes bound to dipeptides or tripeptides, an interaction with hemoglobin was found to be present, the hemoglobin having a strong coordinative site formed by four nitrogen donor atoms. Instead, with copper(II) complexes with TAD or PheANN3, which have the greatest stability. ESR spectra always showed the original species. Only the copper(II) complex with GHL gave rise to a complicated behavior, which contained signals from iron(III) species probably coming from oxidative processes. Encapsulation of all copper(II) complexes in erythrocytes caused a slight oxidative stress, compared to the unloaded and to the native cells. However, no significant differences were observed in the major metabolic properties (GSH, glycolytic rate, hexose monophosphate shunt, Ca(2+)-ATPase) of erythrocytes loaded with different copper(II) complexes, with the exception of methemoglobin levels, which were markedly increased in the case of [Cu(GHL)H-1] compared to [Cu(TAD)]. This latter finding suggests that methemoglobin formation can be affected by the type of complex used for encapsulation, depending on the direct interaction of the copper(II) complex with hemoglobin.
...
PMID:Copper(II) complexes encapsulated in human red blood cells. 759 66

Lead, zinc and copper were administered i.p singly or in combination as acetate salts to rats for 14 consecutive days. It was observed that lead induced drastic changes, copper induced moderate changes but zinc did not cause any significant change in the cholesterol and phospholipid content, hexose, hexosamine and sialic acid levels and activities of the erythrocyte membrane enzymes--acetylcholinesterase (AChE), NADH dehydrogenase and Na(+)-K+ ATPase. In the combined metal treatment the presence of zinc considerably reduced the changes induced by lead and copper.
...
PMID:Metal induced changes in the erythrocyte membrane of rats. 761 77

The intestine is a major site of expression of the human GLUT5 hexose transporter, which is thought to be localized exclusively to the brush border membrane (BBM) where its major role is likely to be in the absorption of fructose. In this study we present novel biochemical and morphological evidence showing that the GLUT5 transporter is also expressed in the basolateral membrane (BLM) of the human intestine. BBM and BLM were isolated by fractionation of human jejunum. BBM were enriched with alkaline phosphatase activity by over 9-fold relative to a crude jejunal homogenate and contained immunoreactive sucrase-isomaltase and GLUT5 proteins. By contrast the BBM fraction was substantially depleted of immunoreactive a1 subunits of the Na,K-ATPase and GLUT2 glucose transporters which were abundantly present in the BLM fraction. This BLM fraction was enriched by over 11-fold in potassium-stimulated phosphatase activity relative to the crude homogenate; BLM also reacted to immunological probes for GLUT5 but showed no observable reactivity with antibodies directed against sucrase-isomaltase. Quantitative immunoblotting revealed that the BBM and BLM contained near equal amounts of GLUT5 per mg of membrane protein. Immunogold localization of GLUT5 on ultrathin sections of human jejunum showed that GLUT5 was present in both apical BBM and BLM. This gold labelling was absent when antiserum was pre-incubated with the antigenic peptide corresponding to a specific C-terminal sequence of human GLUT5. Quantitative analyses of the number of gold particles per unit length of BBM and BLM indicated that the mean density of gold labelling was marginally greater in the BBM (0.399 gold particles/micrometer) than in the BLM (0.293 gold particle/micrometer). The localization of GLUT5 in the BLM of the human jejunum may suggest that it specifically participates in the transfer of fructose across the basal membrane of the enterocyte.
...
PMID:The GLUT5 hexose transporter is also localized to the basolateral membrane of the human jejunum. 761 85

In a previous study [K. Lange and U. Brandt (1993) FEBS Lett. 320, 183-188], we showed that the bulk of the ATP-dependent IP3-sensitive Ca2+ store of the hamster insulinoma cell line, HIT-T15, resides in cell surface-derived vesicles most likely of microvillar origin. The origin and orientation of these vesicles suggested that Ca2+ storage is not due to a membrane-located Ca2+ pumping ATPase but rather to ATP-dependent Ca(2+)-binding within the vesicles. In this case, Ca2+, ATP and IP3 should have free access to the vesicle lumen. This hypothesis was tested. ATP-independent Ca2+ uptake occurred with biphasic kinetics. An initial rapid uptake, which was complete within 30 s, was followed by a slow linear uptake lasting about 10 min. The rapid component was shown by efflux experiments to have an equilibration half-time of about 4 s. This rapid Ca2+ efflux pathway was inhibited by externally applied La3+ (0.1 mM). A similar rapidly equilibrating La(3+)-sensitive Ca2+ pool was also present in vesicles which had been actively loaded with Ca2+ in the presence of ATP. The intravesicular distribution space of this labile Ca2+ pool was identical with that of the non-metabolizable hexose analogue 3-O-methyl-D-glucose, demonstrating that rapid Ca2+ uptake occurs into a true vesicular water space and is not due to binding. ATP and IP3 were also shown to enter the vesicles by an energy-independent pathway which is inhibited by the anion channel inhibitor, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS; 0.5 mM). Both ATP-dependent Ca2+ uptake and IP3-induced Ca2+ release from preloaded vesicles were inhibited by DIDS. These findings clearly demonstrate that (1) the vesicle membrane is permeable to ATP and IP3 via anion channels, and (2) Ca2+ uptake into as well as IP3-induced Ca2+ release from the vesicles occur by passive diffusion through a cation channel which is not regulated by IP3. Consequently, the mechanisms for Ca2+ storage and IP3-induced Ca2+ release must be located in the vesicle lumen. Moreover, the microvillar diffusion-barrier concept, originally proposed for the regulation of hexose transport may also be valid for the receptor-operated regulation of cation and anion influx pathways.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Rapid uptake of calcium, ATP, and inositol 1,4,5-trisphosphate via cation and anion channels into surface-derived vesicles from HIT cells containing the inositol 1,4,5-trisphosphate-sensitive calcium store. 768 9

Glucokinase is distinguished from yeast hexokinase and low Km mammalian hexokinases by its low affinity for glucose and its cooperative behavior, even though glucose binding residues and catalytic residues are highly conserved in all of these forms of hexokinase. The roles of Ser-151 and Asn-166 as determinants of hexose affinity and cooperative behavior of human glucokinase have been evaluated by site-directed mutagenesis, expression and purification of the wild-type and mutant enzymes, and steady-state kinetic analysis. Mutation of Asn-166 to arginine increased apparent affinity for both glucose and ATP by a factor of 3. Mutation of Ser-151 to cysteine, alanine, or glycine lowered the Km for glucose by factors of 2-, 26-, and 40-fold, respectively, decreased Vmax, abolished cooperativity for glucose, and also decreased Km for mannose and fructose. The Ser-151 mutants had hexose Km values similar to those of yeast hexokinase, hexokinase I, and the recombinantly expressed COOH-terminal half of hexokinase I. However, the Ki values for the competitive inhibitors, N-acetylglucosamine and glucose-6-P, were unchanged, suggesting that Ser-151 is not important for inhibitor binding. Mutation of Ser-151 also increased the Km for ATP about 5-fold and abolished the enzyme's low ATPase activity, which indicates it is essential for ATP hydrolysis. The substrate-induced change in intrinsic fluorescence of S151A occurred at a much lower glucose concentration than that for wild-type enzyme. The results implicate a dual role for Ser-151 as a determinant of hexose affinity and catalysis, exclusive of the glucose-induced conformational change, and suggest that the low hexose affinity of glucokinase is dependent on interaction of Ser-151 with other regions of the protein.
...
PMID:Human beta-cell glucokinase. Dual role of Ser-151 in catalysis and hexose affinity. 773 Mar 77

Understanding the molecular mechanisms involved in the regulation of glucose transport into human muscle is necessary to unravel possible defects in glucose uptake associated with insulin resistance in humans. Here we report a strategy to subfractionate human skeletal muscle biopsies (0.5 g) removed from vastus lateralis during a euglycemic insulinemic clamp procedure. A sucrose gradient separated total membranes into five fractions. Fraction 25 (25% sucrose) contained the plasma membrane markers alpha 1- and alpha 2-subunits of the Na(+)-K(+)-adenosinetriphosphatase and the GLUT-5 hexose transporter, recently immunolocalized to the cell surface of human skeletal muscle. The dihydropyridine receptor, a transverse tubule marker, was present exclusively in this fraction. The GLUT-4 glucose transporter was more concentrated in fraction 27.5 (27.5% sucrose) and largely diminished in plasma membrane markers. Open skeletal muscle biopsies were removed before and 30 min after clamping insulin to 550 pM. This increased GLUT-4 protein by 1.61-fold in fraction 25 and lowered it by 50% in fraction 27.5. Thus physiological concentrations of insulin induce translocation of glucose transporters from an internal membrane pool to surface membranes in human skeletal muscle.
...
PMID:Insulin induces translocation of GLUT-4 glucose transporters in human skeletal muscle. 773 59

Saccharomyces cerevisiae and Schizosaccharomyces pombe cells were grown on D-glucose, D-galactose, D-fructose, D-mannose, maltose, trehalose and ethanol. All these substrates were separately added to cells thus grown and the onset and rate of acidification mediated by the plasma membrane H(+)-ATPase were determined. Irrespective of the growth substrate, the best triggers of acidification in both species were fructose, mannose and glucose (with average rates of 5.2, 5.0 and 4.8 nmol H+ per min per mg dry weight, respectively, for S. cerevisiae, and 4.5, 6.8 and 5.8 for S. pombe). These were followed in S. cerevisiae by galactose in Gal-, Man- and Tre-grown cells (about 0.40 nmol H+) and by maltose in Mal- and Tre-grown cells (about 0.15 nmol H+). Trehalose elicited some response in only ethanol-grown cells while ethanol itself was completely ineffective in activating the H(+)-ATPase. In S. pombe, however, maltose caused an acidification rate of 3.6 nmol H+ per min per mg dry wt., followed by EtOH (().38), Gal (0.13) and Tre (0.05). 6-Deoxy-D-glucose and 2-deoxy-D-glucose, not metabolized or improperly metabolized analogues of glucose, had no effect whatsoever. It appears that the sensor triggering the ATPase-activating pathway is a complex responding both to a glucose-type sugar (Glc, Man, Fru) and possibly identical with one of the glucose carriers, and to one of its metabolites, most probably fructose-6-phosphate.
...
PMID:Both glucose-type monosaccharides and one of their metabolites are required for activation of yeast plasma membrane H(+)-ATPase. 780 58

Rat skeletal muscle myofibrils were incubated in the presence of D-glucose, D-fructose, D-galactose, D-ribose, D-tagatose, D-arabinose, D-xylose, D-mannose, L-sorbose, L-rhamnose or DL-glyceraldehyde and myofibrillar ATPase activity as well as the extent of glycation was measured. The attachment of sugars to proteins during glycation was generally dependent on the percentage of a given sugar present in the open-chain form. Glycation resulted in the decrease of myofibrillar ATPase activity. This decrease was low after incubation of myofibrillar proteins with slowly glycating sugars (e.g. glucose) and high with fast glycating sugars (e.g. ribose or glyceraldehyde). ATPase activity was less reduced in the presence of beta-mercaptoethanol.
...
PMID:Glycation of myofibrillar proteins and ATPase activity after incubation with eleven sugars. 805 40


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---