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)

The isoenzyme pattern of hexokinase in rabbit red cells (erythrocytes, fetal erythrocytes and reticulocytes) were determined by means of agarose gel and disc electrophoresis. One duplicated hexokinase (4a and 4b according to the IUPAC-nomenclature) was detected in rabbit erythrocytes as also described for human erythrocytes. Besides the isoenzymes 4a and 4b reticulocytes also contain hexokinase 2 and 3 like rabbit and rat liver. The high KM glucose phosphorylating enzyme, hexokinase 1 could be demonstrated only under specific conditions in the reticulocytes during the initial stage of the anemia. After the fractionation of reticulocyte homogenates the total hexokinase activity was recovered in the mitochondria and cytosol to nearly equal amounts as revealed by the distribution of markers. Hexokinase 2 and 3 were detectable in reticulocytes and in isolated mitochondria only after the addition of certain dissociating agents. In contrast to the tightly bound mitochondrial hexokinases 2 and 3 the type 4a and 4b are more loosely bound and exhibit a bilocal distribution between mitochondria and cytosol of reticulocytes.
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PMID:Electrophoretic characterization and subcellular distribution of hexokinase isoenzymes in red blood cells of rabbits. 53 87

We show by the use of 32P-labeling in vivo that hexokinase 2 and hexokinase 1 in Saccharomyces cerevisiae are phosphoproteins. The highest labeling was after incubation in medium with a low concentration of glucose, when labeling appears to be predominant even without use of immunoprecipitation. The nature of the modification is not known, but it has properties consistent with a phosphomonoester of serine or threonine. The cAMP-dependent protein kinase plays a negative role in hexokinase phosphorylation, in that there was reduced labeling in strains (bcy1) lacking a regulatory subunit, and increased labeling during growth with high concentrations of glucose in a strain attenuated in the catalytic subunit (tpk1w1). The function of the modification is not known, but there was a correlation between the extent of labeling and the expression of kinase-dependent high-affinity glucose uptake.
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PMID:Phosphorylation of yeast hexokinases. 216 41

Hexokinase (ADP: D-hexose-6-phosphotransferase, EC 2.7.1.1) was studied in human thyroid carcinomas (n = 11), follicular adenomas (n = 32), and normal thyroid tissue (n = 21). The specific activity was significantly increased in carcinoma (0.163 +/- 0.083 U/mg protein) compared with normal tissue (0.030 +/- 0.010 U/mg protein) (P less than 0.001). Specific activities of follicular adenomas are rather heterogeneous, but when subdivided into three groups according to histopathologic criteria, a significant difference was found between follicular adenomas group I and II and follicular adenomas group III. A lesser cellular differentiation of adenomas is indicated by the lower degree or even absence of colloid production and follicle formation. A higher proliferation rate may be assumed on the grounds of the irregularities in outline, the often defective pseudocapsule, and signs of compression of the surrounding tissue. The highest specific activity in adenomas was found in the group with the highest proliferative activity, i.e., group III, whereas the lowest specific activities were found in adenomas with the lowest grade of proliferation, i.e., group I; the former was comparable with values found in carcinomas and the latter was comparable with values found in normal thyroid tissue. An interesting difference was found when the compartmentation of hexokinase was compared in carcinomas of different degree of differentiation. In papillary carcinomas a significantly lower proportion of hexokinase (HK) is present in the cytosol in comparison to follicular and undifferentiated carcinomas. In carcinomas more HK II and less HK I was found in comparison with normal thyroid tissue. In contrast hexokinase isozyme composition and compartmentation in adenomas were not different from normal thyroid tissue.
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PMID:Determination and characterization of hexokinase in thyroid cancer and benign neoplasms. 397 45

The enzyme activities and isozyme distribution of some glycolytic enzymes were studied in the K562 cell line before and after induction of hemoglobin formation. Special attention was paid to the three regulator enzymes of glycolysis, hexokinase, phosphofructokinase and pyruvate kinase. Results for the K562 cell line were compared with those for the mature red cell. K562 cells exhibit a relatively low phosphofructokinase and high pyruvate kinase activity. Electrophoresis of hexokinase shows the presence of two bands in the HK I region. HK II is also present, probably as a result of culture conditions. Only 15% of the total hexokinase activity is mitochondrial bound. Phosphofructokinase in K562 cells is mainly composed of the L- and F-types of which the F-type is characteristic for platelets and granulocytes and not for erythrocytes. In the electrophoretic pattern of pyruvate kinase a predominant K4 band besides three hybrids were found. The hybrids were demonstrated to contain L-type subunits of pyruvate kinase, which means a new erythroid marker of K562 cells, as the red cell is the only blood cell that contains L-type pyruvate kinase. Induction experiments with hemin, ARA-C and mitomycin-C gave rise to more than 85% benzidine positive cells after 11 days of culture. The isozyme composition of pyruvate kinase did not change after induction. HK II disappears after induction with ARA-C and mitomycin-C but not with hemin. The results support the idea of the multipotential features of the K562 cell line.
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PMID:Glycolytic enzymes of an erythroleukemic cell line, K562, before and after hemoglobin induction. 622 99

Late committed progenitor cells of erythropoiesis, CFU-E (colony-forming unit--erythroid), were isolated from mouse spleens to near homogeneity by a three-step enrichment procedure. The procedure included a four-day pretreatment of bled mice with the antibiotic thiamphenicol, a recovery period of 3 1/2 days, followed by centrifugal elutriation and Percoll density gradient centrifugation of the spleen cells. This practically pure CFU-E population was used to study some aspects of erythroid differentiation in vitro. Colony growth, as well as morphology and glycolytic enzyme activities of cells isolated at selected times of the 48-hour culture period, were determined. Marked declining activities of several enzymes, including hexokinase, phosphofructokinase, aldolase, enolase, pyruvate kinase, and glucose-6-phosphate dehydrogenase, were observed during in vitro differentiation. The activity of diphosphoglycerate mutase was almost absent in the CFU-E, but progressively increased during differentiation. The isozyme distribution of aldolase and enolase did not change during CFU-E in vitro differentiation into the reticulocyte. Hexokinase (HK) in the CFU-E contained mainly a double-banded type I isozyme, in addition to a minor amount of HK II. During differentiation, a shift was noticed within the double-banded HK I region, whereas HK ii disappeared after one cell division. Pyruvate kinase in the CFU-E was characterized by the presence of both the K-type and the L-type isozyme and hybrids of these isozyme types. During in vitro differentiation, the production of the K-type isozyme rapidly stops in favor of the L type.
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PMID:Changes in activities and isozyme patterns of glycolytic enzymes during erythroid differentiation in vitro. 646 70

In rabbit heart, results show that two isoenzymes of hexokinase (HK) are present. The enzymatic activity associated with mitochondria consists of only one isoenzyme; according to its electrophoretic mobility and its apparent Km for glucose (0.065 mM), it has been identified as type I isoenzyme. The bound HK I exhibits a lower apparent Km for ATPMg than the solubilized enzyme, whereas the apparent Km for glucose is the same for bound and solubilized HK. Detailed studies have been performed to investigate the interactions which take place between the enzyme and the mitochondrial membrane. Neutral salts efficiently solubilize the bound enzyme. Digitonin induces only a partial release of the enzyme bound to mitochondria; this result could be explained by the existence of contacts between the outer and the inner mitochondrial membranes [C. R. Hackenbrock (1968) Proc. Natl. Acad. Sci. USA 61, 598-605]. Furthermore, low concentrations (0.1 mM) of glucose 6-phosphate (G6P) or ATP4- specifically solubilize hexokinase. The solubilizing effect of G6P and ATP4-, which are potent inhibitors of the enzyme, can be prevented by incubation of mitochondria with Pi or Mg2+. In addition, enzyme solubilization by G6P can be reversed by Mg2+ only when the proteolytic treatment of the heart homogenate is omitted during the course of the isolation of mitochondria. These results concerning the interaction of rabbit heart hexokinase with the outer mitochondrial membrane agree with the schematic model proposed by Wilson [(1982) Biophys. J. 37, 18-19] for the brain enzyme. This model involves the existence of two kinds of interactions between HK and mitochondria; a very specific one with the hexokinase-binding protein of the outer mitochondrial membrane, which is suppressed by glucose 6-phosphate, and a less specific, cation-mediated one.
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PMID:Rabbit heart mitochondrial hexokinase: solubilization and general properties. 674 59

Subcellular distribution of hexokinase (HK) isoenzymes in 22 human breast cancers (21 primary cancers and 1 axillary metastatic growth) and 7 non-pathological human mammary gland tissue samples was studied with starch gel electrophoresis on isolated cell fractions obtained by differential centrifugation. Fractions used were cytosol, mitochondria and microsomes. A comparison of two methods for detecting HK activity was made, yielding different results regarding HK II and HK III. A method based on the ability of NADPH to fluoresce in UV gave a constant pattern of HK isoenzymes. In non-pathological breast tissue, only HK I was seen, i.e. in the cytosol and the microsomal fractions. HK I was also seen in all fractions of the cancers, but another more anodal band of HK I, as well as HK II and HK III, consistently appeared in the cytosol fractions. The more commonly used staining technique with tetrazolium dye revealed HK II in 45% and HK III in 50% of the samples. The pattern of HK isoenzymes in the cancers was the same irrespective of estrogen and progesterone cytosolic receptor contents and the histology of the tumors. The fluorescence method is, therefore, much more sensitive than the tetrazolium technique for detecting HK activity after electrophoresis and could explain difference in results obtained by various laboratories.
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PMID:Isoenzyme pattern and subcellular localization of hexokinases in human breast cancer and nonpathological breast tissue. 674 20

Syntheses are described of p1-(adenosine-5')-p3-(glucose-6) triphosphate (Ap3 glucose), Ap4 glucose, and p1-(adenosine-5')-P3-(thymidine-5') triphosphate (Ap3T). The compounds were not substrates of any of the enzymes used in the present studies. Ap3 glucose and Ap4 glucose were inhibitors of yeast hexokinase (HK) and the rat isozymes HK I-III; in general, they had less affinity for the enzymes than the substrates ATP and glucose. Inhibition constants (Ki values) of Ap3T with rat mitochondrial thymidine kinase (M-TK) and rat cytoplasmic TK (C-TK) were determined for variable thymidine (TdR) with a constant saturating level of ATP and for variable ATP with constant saturating TdR. Ap3T was a potent and selective inhibitor of M-TK [KM (TdR)/Ki = 1.6, KM (ATP)/Ki = 38 with variable ATP; KM (TdR) Ki = 0.06, KM (ATP)/Ki = 1.4 with variable TdR] relative to C-TK [KM (TdR)/Ki = 0.006, KM (ATP)/Ki = 0.7 with variable ATP; KM (TdR)/Ki = 0.001, KM (ATP)/Ki = 0.12 with variable TdR]. Inhibition of M-TK and C-TK by Ap3T differed qualitatively and quantitatively from inhibition under the same conditions by the metabolic feedback inhibitor TdR 5'-triphosphate.
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PMID:Species- or isozyme-specific enzyme inhibitors. 6. Synthesis and evaluation of two-substrate condensation products as inhibitors of hexokinases and thymidine kinases. 710 96

Glucose phosphorylating activities were measured in liver extracts from chicks at several developmental stages. Enzyme activity levels in supernates were low (about 0.16 units/g liver) from day 10th of egg incubation until the 17th day, at which time a transient increase to 0.5 units/g was observed. At hatching, the levels were again low (0.15 units/g) compared to adult levels (0.9 units/g). Particulate hexokinase activity was rather constant from day 10th to adulthood (about 0.3 units/g). Chromatography of liver supernates in DEAE-cellulose columns revealed the presence of four hexokinases in embryos up to day 15th of incubation. From that day onwards, the least retained from (hexokinase 4) was no longer found. The most retained form (hexokinase 1) disappeared at hatching, at which time a pattern consisting of hexokinases 2 and 3 was found to be very similar to the adult profile. The four isozymes were characterized as low Km glucose hexokinase of broad sugar specificities and molecular weights of about 100,000. Particulate hexokinase activity of embryonic chick liver was found to be composed of the same isozymes observed in cytosolic extracts. Incubation of particles with glucose 6-P or ATP failed to release hexokinase activity.
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PMID:Ontogeny of chick liver hexokinase isozymes. 734 73

Insulin regulates the activity of key enzymes of glucose metabolism in skeletal muscle by altering transcription or translation or by producing activity-altering modifications of preexisting enzyme molecules. Because of the small size of percutaneous muscle biopsies, these phenomena have been difficult to study in humans. This study was performed to determine how physiological hyperinsulinemia regulates the activities of hexokinase (HK), glycogen synthase (GS), and GLUT-4 in human skeletal muscle in vivo. We determined mRNA abundance, protein content, and activities for these proteins in muscle biopsies before and after a hyperinsulinemic clamp in normal subjects. HK I, HK II, GS, and GLUT-4 were expressed in muscle. HK II accounted for 80% of total HK activity and was increased by insulin from a basal value of 2.11 +/- 0.26 to 3.35 +/- 0.47 pmol.min-1.mg protein-1 (P < 0.05); HK I activity was unaffected. Insulin increased GS activity from 3.85 +/- 0.82 to 6.06 +/- 0.49 nmol.min-1.mg-1 (P < 0.01). HK II mRNA was increased 3.3 +/- 1.3-fold (P < 0.05) by insulin infusion. HK I, GS, and GLUT-4 mRNA and protein were unaffected. Because insulin infusion increased HK II but not GS mRNA, we conclude that HK II and GS may be regulated by insulin by different mechanisms in human skeletal muscle.
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PMID:Regulation of hexokinase II and glycogen synthase mRNA, protein, and activity in human muscle. 748 84


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