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)

Current thought is that proliferating cells undergo a shift from oxidative to glycolytic metabolism, where the energy requirements of the rapidly dividing cell are provided by ATP from glycolysis. Drawing on the hexokinase-mitochondrial acceptor theory of insulin action, this article presents evidence suggesting that the increased binding of hexokinase to porin on mitochondria of cancer cells not only accelerates glycolysis by providing hexokinase with better access to ATP, but also stimulates the TCA cycle by providing the mitochondrion with ADP that acts as an acceptor for phosphoryl groups. Furthermore, this acceleration of the TCA cycle stimulates protein synthesis via two mechanisms: first, by increasing ATP production, and second, by provision of certain amino acids required for protein synthesis, since the amino acids glutamate, alanine, and aspartate are either reduction products or partially oxidized products of the intermediates of glycolysis and the TCA cycle. The utilization of oxygen in the course of the TCA cycle turnover is relatively diminished even though TCA cycle intermediates are being consumed. With partial oxidation of TCA cycle intermediates into amino acids, there is necessarily a reduction in formation of CO2 from pyruvate, seen as a relative diminution in utilization of oxygen in relation to carbon utilization. This has been assumed to be an inhibition of oxygen uptake and therefore a diminution of TCA cycle activity. Therefore a switch from oxidative metabolism to glycolytic metabolism has been assumed (the Crabtree effect). By stimulating both ATP production and protein synthesis for the rapidly dividing cell, the binding of hexokinase to mitochondrial porin lies at the core of proliferative energy metabolism. This article further reviews literature on the binding of the isozymes of hexokinase to porin, and on the evolution of insulin, proposing that intracellular insulin-like proteins directly bind hexokinase to mitochondrial porin.
...
PMID:Hexokinase binding to mitochondria: a basis for proliferative energy metabolism. 938 93

Multiple isoforms of type 1 hexokinase (HK1) are transcribed during spermatogenesis in the mouse, including at least three that are presumably germ cell specific: HK1-sa, HK1-sb, and HK1-sc. Each of these predicted proteins contains a common, germ cell-specific sequence that replaces the porin-binding domain found in somatic HK1. Although HK1 protein is present in mature sperm and is tyrosine phosphorylated, it is not known whether the various potential isoforms are differentially translated and localized within the developing germ cells and mature sperm. Using antipeptide antisera against unique regions of HK1-sa and HK1-sb, it was demonstrated that these isoforms were not found in pachytene spermatocytes, round spermatids, condensing spermatids, or sperm, suggesting that HK1-sa and HK1-sb are not translated during spermatogenesis. Immunoreactivity was detected in protein from round spermatids, condensing spermatids, and mature sperm using an antipeptide antiserum against the common, germ cell-specific region, suggesting that HK1-sc was the only germ cell-specific isoform present in these cells. Two-dimensional SDS-PAGE suggested that all of the sperm HK1-sc was tyrosine phosphorylated, and that the somatic HK1 isoform was not present. Immunoelectron microscopy revealed that HK1-sc was associated with the mitochondria and with the fibrous sheath of the flagellum and was found in discrete clusters in the region of the membranes of the sperm head. The unusual distribution of HK1-sc in sperm suggests novel functions, such as extramitochondrial energy production, and also demonstrates that a hexokinase without a classical porin-binding domain can localize to mitochondria.
...
PMID:Targeting of a germ cell-specific type 1 hexokinase lacking a porin-binding domain to the mitochondria as well as to the head and fibrous sheath of murine spermatozoa. 945 Sep 53

Complexes between hexokinase, outer membrane porin, and the adenylate translocator (ANT) were recently found to establish properties of the mitochondrial permeability transition pore in a reconstituted system. The complex was extracted by 0.5% Triton X-100 from rat brain membranes and separated by anion exchanger chromatography. The molecular weight was approximately 400 kDa suggesting tetramers of hexokinase (monomer 100kDa). By the same method a porin, creatine kinase octamer, ANT complex was isolated and reconstituted in liposomes. Vesicles containing the reconstituted complexes both retained ATP that could be used by either kinase to phosphorylate external creatine or glucose. Atractyloside inhibited this activity indicating that the ANT was involved in this process and was functionally reconstituted. Exclusively from the hexokinase complex containing liposome internal malate or ATP was released by addition of Ca2+ in a N-methylVal-4-cyclosporin sensitive way, suggesting that the hexokinase porin ANT complex might include the permeability transition pore (PTP). The Ca2+ dependent opening of the PTP-like structure was inhibited by ADP (apparent I(50), 8 microM) and ATP (apparent I(50), 84 microM). Also glucose inhibited the PTP-like activity, while glucose-6-phosphate abolished this effect. Although porin and ANT were functionally active in vesicles containing the creatine kinase octamer complex, Ca2+ did not induce a release of internal substrates. However, after dissociation of the creatine kinase octamer, the complex exhibited PTP-like properties and the vesicles liberated internal metabolites upon addition of Ca2+. The latter process was also inhibited by N-methylVal-4-cyclosporin. The activity of peptidyl-prolyl-cis-trans-isomerase (representing cyclophilin) was followed during complex isolation. Cyp D was co-purified with the hexokinase complex, while it was absent in the creatine kinase complex. The inhibitory effect of N-methylVal-4-cyclosporin on the creatine kinase complex may be explained by direct interaction with the creatine kinase dimer that appeared to support octamer formation.
...
PMID:Complexes between porin, hexokinase, mitochondrial creatine kinase and adenylate translocator display properties of the permeability transition pore. Implication for regulation of permeability transition by the kinases. 945 79

Unique type 1 hexokinase (HK1) mRNAs are present in mouse spermatogenic cells (mHk1-s). They encode a spermatogenic cell-specific sequence region (SSR) but not the porin-binding domain (PBD) necessary for HK1 binding to porin on the outer mitochondrial membrane. This study determined the origin of the multiple Hk1-s transcripts in mouse spermatogenic cells and verified that they are translated in mouse spermatogenic cells. It also showed that a single mHk1 gene encodes the mHk1 transcripts of somatic cells and the mHk1-sa and mHk1-sb transcripts of spermatogenic cells, that alternative exons are used during mHk1 gene expression in mouse spermatogenic cells, and that mHK1-S is translated in mouse spermatogenic cells and is localized mainly with the fibrous sheath in the tail region, not with the mitochondria in the midpiece of mouse sperm.
...
PMID:Mouse spermatogenic cell-specific type 1 hexokinase (mHk1-s) transcripts are expressed by alternative splicing from the mHk1 gene and the HK1-S protein is localized mainly in the sperm tail. 950 88

Highly purified adenylate translocase (ANT) from rat heart mitochondria was functionally reconstituted as ATP/ADP exchange carrier in asolectin/cardiolipin vesicles. The ANT preparations used were free of porin, cyclophilin D, and Bax as analysed immunologically and by activity measurements. After pre-loading the ANT-containing proteoliposomes with ATP, malate or AMP, a gradual release of the trapped compounds by increasing the external Ca2+ concentrations could be demonstrated. N-Methyl-Val-4-cyclosporin did not inhibit the Ca2+ dependent release of internal substances from ANT liposomes. This inhibitor was found to be specific for the mitochondrial permeability transition pore (MTP) in intact mitochondria or reconstituted MTP-like protein complexes (e.g. hexokinase, porin, ANT complex). However, ADP in concentrations > 20 microM inhibited the liberation of internal compounds, while in contrast, atractyloside (30 microM) and HgCl2 (5 microM) both induced permeability of the ANT-containing liposomes resulting in a release of trapped substances. These results strongly suggest that ANT itself is capable to adopt a pore-like structure under conditions known to induce the permeability transition in mitochondria.
...
PMID:Reconstituted adenine nucleotide translocase forms a channel for small molecules comparable to the mitochondrial permeability transition pore. 959 86

Heterologous binding of rat brain hexokinase to wild type, porinless, and recombinant yeast mitochondria expressing human porin was assessed, partially characterized, and compared to that in the homologous system (rat liver mitochondria). With porin-containing yeast mitochondria it is shown that (i) a significant, saturable association occurs; (ii) its extent and apparent affinity, correlated with the origin of porin, are enhanced in the presence of dextran; (iii) the binding requires Mg ions and apparently follows a complex cooperative mechanism. This heterologous association does not seem to differ fundamentally from that in the homologous system and represents a good basis for molecular studies in yeast. With porinless yeast mitochondria, binding occurs at much lower affinity, but to many more sites per mitochondrion. The results indicating a major but not exclusive role for porin in the binding are discussed in terms of (i) the mode and mechanism of binding, and (ii) the suitability of the rat hexokinase-yeast mitochondria couple for the study of heterogeneous catalysis in reconstituted cellular model systems.
...
PMID:Binding of rat brain hexokinase to recombinant yeast mitochondria: effect of environmental factors and the source of porin. 973 91

Contact sites between the outer and peripheral inner membrane of mitochondria are involved in protein precursor uptake and energy transfer. Hexokinase and mitochondrial creatine kinase could be attributed by different techniques to the energy transfer contacts. Kinetic analyses suggested a functional interaction between the kinases, outer membrane pore protein, and inner membrane adenylate translocator (ANT). This suggestion was strongly supported by isolation of hexokinase and creatine kinase complexes that were constituted of kinase oligomers, porin and ANT. Phospholipid vesicles carrying reconstituted kinase-porin-ANT complexes enclosed internal ATP in contrast to vesicles containing free porin only. This indicated that unspecific transport through porin was regulated by its interaction with a specific antiporter, ANT. A direct interaction between porin and ANT in the hexokinase complex conferred the reconstituted system with permeability properties reminiscent of the mitochondrial permeability transition (PT) pore. In the creatine kinase complex this interaction between porin and ANT was replaced by contact of both with the kinase octamer. Thus PT-pore-like functions were not observed unless the creatine kinase octamer was dissociated, suggesting that the ANT was locked in the antiporter state by interaction with the octamer. Indeed, reconstituted pure ANT showed PT-pore-like properties concerning Ca2+ sensitivity. However, as cyclophilin was missing, sensitivity against cyclosporin was not observed.
...
PMID:The molecular structure of mitochondrial contact sites. Their role in regulation of energy metabolism and permeability transition. 991 25

Changes in amount and activity of enzyme protein are critical factors in regulating intracellular metabolisms. However, since the metabolisms are proceeding in environment with complex architecture consisted of various membranes, spatial factors should be taken into consideration for the regulation. In this review, involvement of interaction between cytosolic and membrane proteins in metabolic regulation are discussed. It had been reported that hexokinase activity was found in mitochondrial fraction in spite of almost exclusive distribution of other glycolytic enzymes to soluble fraction, the tendency being marked in the brain and many types of tumor cells whereas mitochondrial hexokinase activity was quite low in the liver. Interested in such enzyme and tissue specificities, we investigated the significance and mechanism of the unique intracellular distribution of hexokinase. We found that mitochondria-bound hexokinase was more active than the cytosolic type in producing glucose 6-phosphate (G6P), probably due to the advantage in utilizing ATP produced in mitochondria. In addition, we also found that the binding stabilized hexokinase against G6P inhibition. As to the binding, it was reported that G6P released hexokinase from mitochondria while Mg2+ promoted the binding. In this respect, we found that polyamines promoted the binding at much lower concentration than that of Mg2+, and mitochondria-bound form had small hydrophobic domain at terminal region for the binding to porin on the outer membrane. Then, we found a protease which specifically cleaved the domain with little effect on catalytic activity and molecular size of the bindable form. Such a modifying protease was purified and identified as lysosomal cathepsin L. The protease activity was high in the liver and low in the brain, suggesting that the difference in the activity was responsible for the afore-mentioned tissue specificity. On the other hand, we examined regulatory mechanism for active oxygen production in neutrophils, since the production of superoxide anion (O2-) by NADPH oxidase was very low at the resting state while markedly increased on phagocytosis and chemical stimulation. Since the stimulants for the activation were so various in chemical nature, we postulated mechanism to converge the stimulation to the activation. Incidentally, we found increase in phosphorylation of 46-47 K protein, irrespective of the type of stimulation. Use of inhibitors and examination on the phosphorylation condition indicated protein kinase C (PKC) as the phosphorylating enzyme. In addition, we observed the 46-47 K protein existed in cytosol at resting state, while it was translocated to cell membranes in concurrence with the phosphorylation. Similar findings were obtained in many laboratories and those proteins were named cytosolic activating factors (and then p47-phox, etc.). These proteins associate with membrane proteins to constitutes the active from of NADPH oxidase. Next, we examined mechanism to shut off the O2- production, and found that the inactivation through disassembly of the constituents was attained by dephosphorylation of phosphorylated p47-phox by cytosolic protein phosphatase. Then we have also found that protein kinases other than PKC were involved in regulation of NADPH oxidase activity. Though phosphorylation of p47-phox etc. is deeply involved in the activation of NADPH oxidase, membrane perturbation, so-called priming, is required for the activation. We also reported some possible indications for the priming, and possible involvement of cytoskeletons in O2- production. Apart from protein phosphorylation, it has been reported that amphiphilic acidic compounds are potent activator for NADPH oxidase. We also have examined their effects to find that these compounds also caused the assembly of the NADPH oxidase constituents. Reversely, amphiphilic basic compounds suppressed suggesting significance of introduction of negative charge in NADPH oxidase activat
...
PMID:[Cooperation of membrane proteins and cytosolic proteins in metabolic regulation--involvement of binding of hexokinase to mitochondria in regulation of glucose metabolism and association and complex formation between membrane proteins and cytosolic proteins in regulation of active oxygen production]. 992 8

A Triton X-100 extract from rat brain mitochondria was obtained using low detergent/protein ratio. From this extract a proteinaceous complex was purified; its molecular weight was as high as 880 kD. The complex contained both hexokinase and creatine kinase activity. When incorporated into phospholipid bilayer membranes, the complex formed a channel whose activity was different than the channel activity of purified porin isolated either by adsorption chromatography or by dissociation from protein complexes. A ligand of the mitochondrial benzodiazepine receptor (Ro5-4864) in submicromolar concentrations had an apparent influence on the kinetic behavior of enzymatic coupling of hexokinase and creatine kinase. It is suggested that the 880-kD complex is formed by mitochondrial contact sites. The role of the isolated protein complex in the formation of nonspecific permeability in mitochondria is discussed.
...
PMID:Proteinaceous complexes from mitochondrial contact sites. 1023 91

The transport of activated fatty acids across the mitochondrial outer membrane has not been fully addressed. A polyanion (M(n)=22 kDa) inhibited the ADP-stimulated carnitine-dependent oxidation of both palmitoyl-CoA and palmitate plus CoA as well as mitochondrial hexokinase binding. In contrast, the oxidation of palmitoylcarnitine plus malate, as well as glutamate oxidation, was essentially unaffected. Mitochondrial carnitine palmitoyltransferase-1 was not inhibited by the polyanion. The data suggest an additional component in carnitine-dependent mitochondrial fatty acid oxidation, possibly porin.
...
PMID:A 22 kDa polyanion inhibits carnitine-dependent fatty acid oxidation in rat liver mitochondria. 1054 43


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

---