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)

In this study, glucose repression in Saccharomyces cerevisiae was analysed under defined physiological conditions, at both the molecular and physiological levels, by pulsing glucose to a galactose-limited continuous culture. During this pulse of glucose, the galactose feed was kept constant. Directly after the glucose pulse, carbon dioxide production increased while oxygen consumption remained constant, demonstrating that the surplus of glucose had been consumed by means of fermentation. The direct accumulation of galactose in the medium after the glucose pulse indicated that the consumption of galactose had been stopped instantaneously. Galactose uptake experiments revealed that the galactose transporter was still present but apparently was incapable of galactose uptake, which could be due to inhibition of the galactose transporter by glucose. The total concentration of cAMP increased from 5 nmol g-1 at t = 0 to 25 nmol g-1 at t = 1.5 min. After 2 min the concentration of cAMP gradually decreased again to the normal level. Within 2 min after the addition of glucose, the transcription of the GAL genes and SUC2 was inhibited. In addition, the transcription of the HXK1 gene, encoding hexokinase isoenzyme 1, was also inhibited, which demonstrates that the HXK1 gene is regulated at the transcriptional level comparable with invertase.
...
PMID:Analysis of glucose repression in Saccharomyces cerevisiae by pulsing glucose to a galactose-limited continuous culture. 133 40

mRNA steady-state levels and activities of enzymes of intermediary carbon metabolism (hexokinase, phosphoglucoisomerase, phosphofructokinase, glucose-6-phosphate dehydrogenase, phosphoglucomutase) and glucose-regulated enzymes (pyruvate decarboxylase, pyruvate dehydrogenase, invertase, alcohol dehydrogenase) were determined in glucose-limited continuous cultures of an industrial strain of Saccharomyces cerevisiae at different dilution rates (D) ranging from 0.05 to 0.315 h-1. The activity of most enzymes measured remained constant over this range except for alcohol dehydrogenase I/II which decreased proportionally with increasing dilution rate. A decrease in phosphoglucomutase activity occurred with increasing dilution rate but reached a minimum at D 0.2 h-1 and from thereon remained constant. A decrease in pyruvate decarboxylase activity and a slight decrease in phosphoglucoisomerase activity was observed. At D 0.29/0.315 h-1, at the onset of the Crabtree effect, most glycolytic enzymes remained constant except for pyruvate decarboxylase and glucose-6-phosphate dehydrogenase which increased at D 0.315 h-1 and alcohol dehydrogenase I/II which decreased. The ADHI/II and PDC1 mRNA levels obtained at the different dilution rates were in accordance with the activity measurements. The mRNA level of HXK1 decreased with increasing dilution rates, whereas the transcription of HXK2 increased. Pyruvate dehydrogenase (PDA1) and PGI1 mRNA fluctuated but no significant change could be detected. These results indicate that there is no transcriptional or translational regulation of glycolytic flux between D 0.05 h-1 and 0.315 h-1 except at the branch point between oxidative and fermentative metabolism (pyruvate decarboxylase/pyruvate dehydrogenase) at D 0.315 h-1. Surprisingly regulation of the Crabtree effect does not seem to involve transcriptional regulation of PDA1.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Analysis of transcription and translation of glycolytic enzymes in glucose-limited continuous cultures of Saccharomyces cerevisiae. 148 26

The hexokinase (HK) of the human red blood cell (RBC) was separated into two distinct major isozymes by fast protein liquid chromatography using a linear salt gradient on a MonoQ column. The first isozyme (HKI) eluted as a sharp peak at the same position as HKI of human liver. The second isozyme eluted between HKI and HKII of human white blood cells, and it appeared to be unique to the RBC (it was designated HKR). From a gel filtration column, HKR eluted before HKI, suggesting that it was larger than HKI by several kilodaltons. In a mitochondria-enriched fraction from human reticulocytes, no HKR was found; thus, HKR was not a mitochondrial enzyme. Despite these differences in chromatographic behavior, size, and mitochondrial binding, both forms behaved kinetically as HKI. RBC from normal blood contained HKI and HKR at an equal activity, but in reticulocyte-rich RBC, HKR dominated. When RBC of increasing age was separated by buoyant density ultracentrifugation, the total HK activity decayed in a biphasic manner, with half-lives respectively of approximately 15 and approximately 51 days. When isolated by MonoQ column from each age-separated fraction, HKR was the major form in the youngest RBC, and decreased rapidly with cell age, with a t 1/2 of approximately 10 days, representing a negligible activity in the oldest RBC. Instead, HKI was relatively stable through the entire life span of the RBC, with a t 1/2 of approximately 66 days. Thus, HKR appears to be an RBC-specific isozyme that is predominant in the reticulocyte and is then rapidly degraded. During maturation of the RBC, the fast decay of HKR contributes to the early sharp decline of HK activity and the slow decay of HKI to the later gradual decline.
...
PMID:An isozyme of hexokinase specific for the human red blood cell (HKR) 238 63

Saccharomyces cerevisiae has two homologous hexokinases, I and II; they are 78% identical at the amino acid level. Either enzyme allows yeast cells to ferment fructose. Mutant strains without any hexokinase can still grow on glucose by using a third enzyme, glucokinase. Hexokinase II has been implicated in the control of catabolite repression in yeasts. We constructed null mutations in both hexokinase genes, HXK1 and HXK2, and studied their effect on the fermentation of fructose and on catabolite repression of three different genes in yeasts: SUC2, CYC1, and GAL10. The results indicate that hxk1 or hxk2 single null mutants can ferment fructose but that hxk1 hxk2 double mutants cannot. The hxk2 single mutant, as well as the double mutant, failed to show catabolite repression in all three systems, while the hxk1 null mutation had little or no effect on catabolite repression.
...
PMID:Effects of null mutations in the hexokinase genes of Saccharomyces cerevisiae on catabolite repression. 354 Jun 5

The nucleotide sequence of the yeast glycolytic hexokinase isoenzyme PI-gene, HXK1, has been determined by sequencing the yeast DNA insert of the previously isolated plasmid HXK1 clone [Entian et al., Mol. Gen. Genet. 198 (1984) 50-54]. The structural gene sequence included 1452 bp coding for 484 amino acid (aa) residues corresponding to the Mr of 153 605 for the HXK1 monomer. Several initiation regions and termination points were located using nuclease S1 mapping. The HXK1 sequence was 76% homologous with that of HXK2, which is responsible for triggering glucose repression in yeasts. Since HXK1 is not involved in this regulatory system, the regulatory function of HXK2 must correspond to one or more of the differences between both isoenzymes. Most changes in the amino acid sequence were statistically distributed; however, four clustered regions with more than five altered aa residues were identified.
...
PMID:Complete nucleotide sequence of the hexokinase PI gene (HXK1) of Saccharomyces cerevisiae. 390 24

Uptake of glucose, fructose, and the nonmetabolizable analog 6-deoxyglucose was measured in wild-type Saccharomyces cerevisiae and two mutant strains, one (hxk1 hxk2) lacking both hexokinase A(P-I) and B(P-II) but containing glucokinase (and hence able to grow on glucose but not fructose) and the other (hxk1 hxk2 glk) also lacking glucokinase (and not able to grow on glucose either). Uptake of the nonmetabolized substances (i.e., 6-deoxyglucose in all three strains, fructose in the two mutants, and glucose in the triple mutant) reached a plateau at or below the external concentration. The kinetic characteristics of uptake were determined from 5-sec incubations by plotting velocity (V) vs. velocity/substrate concentration (V/S) curves. According to such plots, in the wild-type strain uptake had two components, "high affinity uptake" with Km values of ca. 1 mM for glucose and 6 mM for fructose and "low affinity uptake" with Km values of ca. 20 and 50 mM, respectively. The double kinase mutant showed both components for glucose but only the high Km component for fructose, while the triple kinase mutant showed only high Km uptake for both glucose and fructose. Genetic analysis showed that only in strains lacking both hexokinases (hxk1 hxk2) was the low Km system for fructose absent. Low Km uptake was restored to the triple mutant by introduction of the cloned wild-type genes: HXK1 or HXK2, for fructose uptake, and HXK1, HXK2, or GLK1, for glucose uptake. A phosphoglucose isomerase mutant had both low and high Km uptake for glucose. These results indicate the presence of two types of uptake mechanism for glucose and fructose in yeast, the functioning of one of which, the low Km system, is influenced by the cognate kinases.
...
PMID:Involvement of kinases in glucose and fructose uptake by Saccharomyces cerevisiae. 630 Aug 72

Mutants of Saccharomyces cerevisiae lacking glucokinase (EC 2.7.1.2) have no discernible phenotypic difference from the wild-type strain; in a hexokinaseless background, however, they are unable to grow on any sugar except galactose. Reversion studies with glucokinase mutants indicate that the yeast S. cerevisiae has no other enzyme for phosphorylating glucose except the two hexokinases, P1 and P2, and glucokinase. Spontaneous revertants of hxk1 hxk2 glk1 strains collected on glucose regain any one of these three enzymes. The majority of glucokinase revertants synthesize species of enzyme activity that are kinetically or otherwise indistinguishable from the wild-type enzyme. In a few cases the reverted enzyme is very perceptibly altered in properties with a Km for glucose two orders of magnitude higher than that of the enzyme from the wild-type parent. These recessive, noncomplementing mutants, thus, define a single structural gene GLK1 of glucokinase. Yeast diploids lacking all of the three enzymes for glucose phosphorylation fail to sporulate. Heterozygosity of either of the hexokinase genes HXK1 or HXK2, but not GLK1, restores sporulation. The location of GLK1 on chromosome III was indicated by loss of this chromosome when hexokinaseless diploids heterozygous for glk1 were selected for resistance to 2-deoxyglucose; the homologue of chromosome III carrying GLK1, the mating-type allele and other nutritional markers on this chromosome was lost. Meiotic mapping of glucokinase executed with heterozygosity of one of the hexokinases indicated that the gene GLK1 defining the structure of glucokinase protein is located on the left arm of chromosome III 24 cM to the left of his4 in the order: leu2--his4--glk1. --Only two of 206 independent glucokinase mutants are nonsense ochre, both of which map at one end of the gene. In hxk1 only one of 130 isolates is a nonsense mutation, whereas in hxk2 none has been found among 220 independent mutants. These results raise the possibility that the protein products of these genes have some other essential function. --An earlier mapping result for hxk2 has been corrected. The new location is on the left arm of chromosome VII, 17 cM distal to ade5 in the order: lys5--ade5--hxk2.
...
PMID:Genetics of yeast glucokinase. 635 42

The hexokinases, by converting glucose to glucose-6-phosphate, help maintain the downhill gradient that results in movement of glucose into cells through the facilitative glucose transporters. GLUT4 and hexokinase (HK) II are the major transporter and hexokinase isoforms in skeletal muscle, heart, and adipose tissue, wherein insulin promotes glucose utilization. To understand whether hormones influence the contribution of phosphorylation to cellular glucose utilization, we investigated the effects that catecholamines, cyclic AMP (cAMP), and insulin have on HKII gene expression in cells representative of muscle (L6 cells) and brown (BFC-1B cells) and white (3T3-F442A cells) adipose tissues. Isoproterenol or the cAMP analog 8-chlorophenylthio-cAMP selectively increase HKII gene transcription in L6 cells, as does insulin (Printz RL, Koch S, Potter LP, O'Doherty RM, Tiesinga JJ, Moritz S, Granner DK: Hexokinase II mRNA and gene structure, regulation by insulin, and evolution. J Biol Chem 268:5209-5219, 1993), and cause a concentration- and time-dependent increase of HKII mRNA in both muscle and fat cell lines without changing HKI mRNA. Isoproterenol and insulin also increase the rate of synthesis of HKII protein and increase glucose phosphorylation and glucose utilization in L6 cells.
...
PMID:Regulation of hexokinase II gene transcription and glucose phosphorylation by catecholamines, cyclic AMP, and insulin. 758 50

Glucose-repressed growth of Saccharomyces cerevisiae was analysed in a nitrogen-limited continuous culture at different dilution rates (D). The glucose consumption of the yeast decreased from 3.4 g g-1 h-1 to 3.0 g g-1 h-1 when D was decreased from 0.3 h-1 to 0.15 h-1. No transcripts of the SUC2 and HXK1 genes, encoding, respectively, invertase and hexokinase isoenzyme 1, could be detected. Because both genes are regulated by glucose repression at the transcriptional level, this confirmed that the culture was glucose repressed at every D. During the decrease in D, no change in the activities or mRNA levels of key enzymes in carbon metabolism was observed, except for alcohol dehydrogenases I and II and phosphoglucomutase. These enzymes increased in activity and/or mRNA level when D was decreased, which was also observed in glucose- and galactose-limited continuous cultures. This demonstrates that the expression levels of alcohol dehydrogenases I and II, and also phosphoglucomutase, are coupled to the growth rate of the organism. A comparison between the alcohol dehydrogenase II activity in glucose- and nitrogen-limited continuous cultures demonstrated that the growth rate contributes as much to repression of alcohol dehydrogenase II activity as does glucose. Both the glucose consumption and the activity of the glycolytic enzymes were relatively constant when D was decreased and, as a consequence, the concentrations of intracellular metabolites remained constant. A slight decrease in the glucose 6-phosphate concentration was observed, which could be caused by the slight decrease in glucose consumption at low D values.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:A nitrogen-limited, glucose-repressed, continuous culture of Saccharomyces cerevisiae. 801 81

Glucose metabolism and glucose-stimulated insulin secretion are thought to be controlled at the level of glucose phosphorylation in pancreatic islet beta-cells. In the current study we have investigated the importance of glucose phosphorylation by using recombinant adenovirus as a gene delivery system for isolated rat islets. Treatment of islets with a virus containing the cDNA encoding the Escherichia coli beta-galactosidase gene (AdCMV-beta GAL) resulted in efficiencies of gene transfer of 70.3 +/- 2.5 and 61.2 +/- 2.2% in two independent experiments. Treatment of islets with a virus containing the cDNA encoding rat hexokinase I (AdCMV-HKI) resulted in a 10.7-fold increase in immunodetectable hexokinase protein and a similar increase in enzyme activity. A large percentage of the overexpressed hexokinase activity was associated with a cell fraction enriched in mitochondria. These changes in enzyme level were accompanied by a 2-fold increase in insulin release and [5-3H]glucose usage at basal glucose concentrations (3 mM). The rate of glucose usage at 20 mM glucose and the magnitude of the insulin secretory response to this stimulatory level of the sugar were unchanged relative to control islets. Overexpression of hexokinase I in isolated islets therefore creates a phenotype of elevated basal insulin release similar to that seen in islets from obese and insulin-resistant mammals. The discrepancy between the large increase in hexokinase activity and the small increase in glucose usage and insulin release may indicate, however, that other steps in glucose metabolism become rate-limiting after only modest increases in glucose-phosphorylating activity.
...
PMID:Overexpression of hexokinase I in isolated islets of Langerhans via recombinant adenovirus. Enhancement of glucose metabolism and insulin secretion at basal but not stimulatory glucose levels. 806 45


1 2 3 4 5 Next >>

---