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)

Phytomonas sp. isolated from Euphorbia characias was adapted to SDM-79 medium. Cells isolated in the early stationary phase of growth were analyzed for their capacity to utilize plant carbohydrates for their energy requirements. The cellulose-degrading enzymes amylase, amylomaltase, invertase, carboxymethylcellulase, and the pectin-degrading enzymes polygalacturonase and oligo-D-galactosiduronate lyase were present in Phytomonas sp. and were all, except for amylomaltase, excreted into the external medium. Glucose, fructose and mannose served as the major energy substrates. Catabolism of carbohydrates occurred mainly via aerobic glycolysis according to the Embden-Meyerhof pathway, of which all the enzymes were detected. Likewise, the end-products of glycolysis, acetate and pyruvate, glycerol, succinate and ethanol were detected in the culture medium, as were the enzymes responsible for their production. Mitochondria were incapable of oxidizing succinate, 2-oxoglutarate, pyruvate, malate and proline, but had a high capacity to oxidize glycerol 3-phosphate. This oxidation was completely inhibited by salicylhydroxamic acid. No cytochromes could be detected either in intact mitochondria or in sub-mitochondrial particles. Mitochondrial respiration was not inhibited by antimycin, azide or cyanide. The glycolytic enzymes, from hexokinase to phosphoglycerate kinase, and the enzymes glycerol kinase, glycerol-3-phosphate dehydrogenase, phosphoenolpyruvate carboxykinase, malate dehydrogenase and adenylate kinase, were all associated with glycosomes that had a buoyant density of about 1.24 g cm-1 in sucrose. Cytochemical staining revealed the presence of catalase in these organelles. The cytosolic enzyme pyruvate kinase was activated by fructose 2,6-bisphosphate, typical of all other pyruvate kinases from Kinetoplastida. The energy metabolism of the plant parasite Phytomonas sp. isolated from E. characias resembled that of the bloodstream form of the mammalian parasite Trypanosoma brucei.
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PMID:Characterization of carbohydrate metabolism and demonstration of glycosomes in a Phytomonas sp. isolated from Euphorbia characias. 143 59

The mutual adjustment of glucose uptake and metabolism in the insect stage of the protozoan parasite Trypanosoma brucei was studied. T. brucei was preadapted in the chemostat to conditions in which either glucose or proline served as the major carbon and energy source. Cells were grown and adapted to either energy or non-energy limitation at a low dilution rate (0.5 day-1) or a high dilution rate (1 day-1). The cells were then used in short- to medium-term uptake experiments with D-[14C]glucose as a tracer. In time course experiments a steady state was reached after 15 min regardless of the preadaptation conditions. This steady-state level increased with increasing glucose availability during preadaptation. The rate of glucose uptake and the hexokinase activity were linearly correlated. In short-term 5- to 90-s) uptake experiments a high transport rate was measured with cultures grown in excess glucose, an intermediate rate was measured with proline-grown cultures, and a low rate was measured in organisms grown under glucose limitation. Glucose metabolism and proline metabolism did not affect each other during the 15-min incubations. Glucose uptake, as a function of the external glucose concentration, did not obey simple Michaelis-Menten kinetics but could be described by a two-step mechanism: (i) transport of glucose by facilitated diffusion and (ii) subsequent metabolism of glucose. The respective rates of the two steps were adjusted to each other. It is concluded that T. brucei is capable of adjusting the different metabolic processes in a way that gives maximum energy efficiency at the cost of short-term flexibility.
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PMID:Mutual adjustment of glucose uptake and metabolism in Trypanosoma brucei grown in a chemostat. 173 18

Saccharomyces cerevisiae glucokinase (GLK) is the only described hexose-phosphorylating enzyme specific for aldo-hexoses. The gene was cloned by complementation of a triple mutant lacking all hexose-phosphorylating isoenzymes. Restriction sites were confirmed by genomic hybridization and GLK1 was mapped on chromosome III by ROFAGE, a method derived from the orthogonal field alteration gel electrophoresis. The mapping data were in agreement with previous genetic data. The open reading frame was established by two transcription start points in front of the initial ATG codon and by C-terminal beta-galactosidase fusions. The mRNA is 1.75 kb long and codes for 500 amino acid (aa) residues. Diversity of GLK from hexokinases PI and PII is very marked, with only 26 and 28% overall aa homology. A central core of about 350 aa shows 39% homology. No cross-hybridization could be observed by Southern hybridization. However, strong homologies were found over a range of 11 aa between glucokinase, yeast hexokinases (PI, PII) and rat hexokinase with 8 aa in common. These strongly conserved homologies give support to the view that this aa region corresponds to the binding site for glucose. Unlike all other hexose-phosphorylating enzymes, there is no proline residue indicating a conformational turn next to this glucokinase region. This finding may explain the failure of fructose phosphorylation. In both GLK and the hexokinases, a lysine residue is also conserved at aa position 110 which probably corresponds to the ATP-binding site. Additionally, a consensus sequence of 8 aa residues which is common for ATP-binding enzymes is conserved within the C-terminal part of GLK. The codon bias index for GLK1 is 0.25, which is very low compared with other glycolytic enzymes described so far. The gene is moderately expressed and constitutive on different carbon sources investigated. GLK1 null alleles had no detectable effects on sporulation and growth. Hence, a physiological role for GLK, which might explain its preservation, could not be detected under our laboratory test conditions.
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PMID:Structure of yeast glucokinase, a strongly diverged specific aldo-hexose-phosphorylating isoenzyme. 307 53

Herpetomonas roitmani, a non-pathogenic trypanosomatid was grown in chemically defined media either containing proline or glucose as carbon source. Using transmission electron microscopy we observed that cells grown in the presence of proline present more lipid inclusions, and a larger mitochondrion with more cristae and higher activity of succinate cytochrome c reductase. On the other hand, cells grown with glucose as carbon source had more glycosomes, which were preferentially located close to the bacterium endosymbiont, and a much higher activity of hexokinase, a typical glycosome marker. Three-dimensional reconstruction and morphometrical analysis confirm these observations. The number of promastigotes of H. roitmani increased in the presence of proline. Taken together these results indicate that the growth conditions markedly influenced the ultrastructure and the metabolism of H. roitmani.
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PMID:Biochemical and ultrastructural changes in Herpetomonas roitmani related to the energy metabolism. 1076 96

The widely accepted idea that bees fuel flight through the oxidation of carbohydrate is based on studies of only a few species. We tested this hypothesis as part of our research program to investigate the size-dependence of flight energetics in Panamanian orchid bees. We succeeded in measuring rates of O(2) consumption and CO(2) production in vivo during hovering flight, as well as maximal activities (V(max) values) in vitro of key enzymes in flight muscle energy metabolism in nine species belonging to four genera. Respiratory quotients (ratios of rates of CO(2) production to O(2) consumption) in all nine species are close to 1.0. This indicates that carbohydrate is the main fuel used for flight. Trehalase, glycogen phosphorylase and hexokinase activities are sufficient to account for the glycolytic flux rates estimated from rates of CO(2) production. High activities of other glycolytic enzymes, as well as high activities of mitochondrial oxidative enzymes, are consistent with the estimated rates of carbohydrate-fueled oxidative metabolism. In contrast, hydroxyacylCoA dehydrogenase, an enzyme involved in fatty acid oxidation, was not detectable in any species. Thoracic homogenates displayed ADP-stimulated oxidition of pyruvate + proline, but did not oxidize palmitoyl l-carnitine + proline as substrates. A metabolic map, based on data reported herein and information from the literature, is presented. The evidence available supports the hypothesis that carbohydrate serves as the main fuel for flight in bees.
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PMID:Energy metabolism in orchid bee flight muscles: carbohydrate fuels all. 1615 28

Molecular studies of the genome of the fungus Coccidioides have demonstrated two nearly identical, but well-identified species, Coccidioides immitis and C. posadasii, known as "California" and "non-California" species, respectively. The objective of this study was to determine, through molecular methods, whether both species of Coccidioides are present in Mexican patients with coccidioidomycosis and to estimate, their geographical distribution in Mexico. We analyzed 56 clinical isolates of Coccidioides spp. from Mexican patients. Molecular identification of each strain was done by means of real time PCR using TaqMan(R) probes to amplify single nucleotide polymorphisms (SNPs) in four target sequences, loci, named proline 157, proline 174, hexokinase 149 and glucose-synthase 192. SNP analysis identified two of the 56 isolates as Coccidioides immitis and the remaining 54 as C. posadasii. The dual probe assay that included proline 157, proline 174 and glucose-synthase 192 gave consistent results on SNP differentiation between the two species. In contrast, the template matching hexokinase 149 gave negative results for any species in 34 samples. Our results did not show geographical overlap of the species, and they also confirmed that C. posadasii is the most frequent species in Mexico. A vast majority of C. posadasii strains were localized in the north-central region of the country.
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PMID:Molecular identification of coccidioides isolates from Mexican patients. 1734 38

Glucokinase (GCK, hexokinase IV) is a monomeric enzyme with a single glucose binding site that displays steady-state kinetic cooperativity, a functional characteristic that affords allosteric regulation of GCK activity. Structural evidence suggests that connecting loop I, comprised of residues 47-71, facilitates cooperativity by dictating the rate and scope of motions between the large and small domains of GCK. Here we investigate the impact of varying the length and amino acid sequence of connecting loop I upon GCK cooperativity. We find that sequential, single amino acid deletions from the C-terminus of connecting loop I cause systematic decreases in cooperativity. Deleting up to two loop residues leaves the kcat value unchanged; however, removing three or more residues reduces kcat by 1000-fold. In contrast, the glucose K0.5 and KD values are unaffected by shortening the connecting loop by up to six residues. Substituting alanine or glycine for proline-66, which adopts a cis conformation in some GCK crystal structures, does not alter cooperativity, indicating that cis/trans isomerization of this loop residue does not govern slow conformational reorganizations linked to hysteresis. Replacing connecting loop I with the corresponding loop sequence from the catalytic domain of the noncooperative isozyme human hexokinase I (HK-I) eliminates cooperativity without impacting the kcat and glucose K0.5 values. Our results indicate that catalytic turnover requires a minimal length of connecting loop I, whereas the loop has little impact upon the binding affinity of GCK for glucose. We propose a model in which the primary structure of connecting loop I affects cooperativity by influencing conformational dynamics, without altering the equilibrium distribution of GCK conformations.
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PMID:Role of connecting loop I in catalysis and allosteric regulation of human glucokinase. 2472 72