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)

Crystalline arrays are induced in outer membranes of rat-liver and rat-heart mitochondria by phosphotungstate and silicotungstate. The basic structure of the arrays has been determined by correlation averaging of electron microscopic images of side views of tubular arrays and en face views of planar arrays. The arrays consist of rows of bilobed projecting subunits and are similar (in lattice parameters and projected subunit dimensions) to periodic arrays of ion transport ATPases, e.g., arrays of Ca(2+)-ATPase induced by vanadate in sarcoplasmic reticulum. Hexokinase-labeled colloidal gold particles do not specifically decorate the arrays, suggesting that the hexokinase receptor (VDAC channel) is not a component of the arrays.
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PMID:Structure of paracrystalline arrays on outer membranes of rat-liver and rat-heart mitochondria. 147 29

The outer mitochondrial membrane receptor for hexokinase binding has been identified as the VDAC protein, also known as mitochondrial porin. The ability of the receptor to bind hexokinase is inhibited by pretreatment with dicyclohexylcarbodiimide (DCCD). At low concentrations, DCCD inhibits hexokinase binding by covalently labeling the VDAC protein, with no apparent effect on VDAC channel-forming activity. The stoichiometry of [14C]-DCCD labeling is consistent with one to two high-affinity DCCD-binding sites per VDAC monomer. A comparison between the sequence of yeast VDAC and a conserved sequence found at DCCD-binding sites of several membrane proteins showed two sites where the yeast VDAC amino acid sequence appears to be very similar to the conserved DCCD-binding sequence. Both of these sites are located near the C-terminal end of yeast VDAC (residues 257-265 and 275-283). These results are consistent with a model in which the C-terminal end of VDAC is involved in binding to the N-terminal end of hexokinase.
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PMID:Hexokinase-binding properties of the mitochondrial VDAC protein: inhibition by DCCD and location of putative DCCD-binding sites. 247 32

In rapidly growing, highly glycolytic hepatoma cells as much as 65% of the total cell hexokinase is bound to the outer mitochondrial membrane [Parry, D.M., & Pedersen, P.L. (1983) J. Biol. Chem. 258, 10904-10912]. In this paper, we describe the purification to apparent homogeneity of a mitochondrial pore-forming protein from the highly glycolytic AS-30D rat hepatoma cell line. The purified protein shows a single 35 000-dalton band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis, an amino acid composition slightly more hydrophobic than that of the rat liver pore protein (also known as VDAC or mitochondrial porin), and a channel-forming activity of 136 channels min-1 (microgram of protein)-1. In addition to displaying the properties characteristic of VDAC (single-channel conductance, voltage dependence, and preference for anions), we observe that the AS-30D VDAC protein is one of only three mitochondrial proteins that bind [14C]dicyclohexylcarbodiimide (DCCD) at relatively low dosages (2 nmol of DCCD/mg of mitochondrial protein). Significantly, treatment of intact mitochondria isolated from either rat liver or the AS-30D hepatoma with DCCD results in an almost complete inhibition of their ability to binding hexokinase. Fifty percent inhibition of binding occurs at less than 2 nmol of DCCD/mg of mitochondrial protein. In contrast to DCCD, water-soluble carbodiimides are without effect on hexokinase binding. These results suggest that the pore-forming protein of tumor mitochondria forms at least part of the hexokinase receptor complex. In addition, they indicate that a carboxyl residue located within a hydrophobic region of the receptor complex may play a critical role in hexokinase binding.
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PMID:Hexokinase receptor complex in hepatoma mitochondria: evidence from N,N'-dicyclohexylcarbodiimide-labeling studies for the involvement of the pore-forming protein VDAC. 300 16

The mitochondrial porin or VDAC (Voltage-Dependent Anion Channel), the pore-forming structure responsible for the high permeability of the outer mitochondrial membrane, was found to be one of only three mitochondrial proteins bound by [14C]dicyclohexylcarbodiimide (DCCD) at low dosages (1.5 nmol/mg of mitochondrial porin) (De Pinto, V., Tommasino, M., Benz, R., and Palmieri, F. (1985) Biochim. Biophys. Acta 813, 230-242). Treatment of intact mitochondria with DCCD results in the inhibition of their ability to binding hexokinase (Nakashima, R. A., Mangan, P. S., Colombini, M., and Pedersen, P. L. (1986) Biochemistry 25, 1015-1021). In the present study, mitochondrial porin was purified from [14C]DCCD-labeled mitochondria. The purified labeled porin was treated with the cleavage reagent CNBr and with the endoproteases trypsin and V8 from Staphylococcus aureus and blotted to polyvinylidene difluoride membrane. The transferred peptides were detected with Coomassie Blue dye, excised, and sequenced. The sequences of several labeled and unlabeled peptides were obtained and then overlapped. The region containing the [14C]DCCD radioactivity was limited to 50 amino acid residues and completely sequenced. Covalently incorporated [14C]DCCD was exclusively released at the position corresponding to glutamate 72. The DCCD-reactive residue is located in the 4th of 16 predicted transmembrane amphipathic beta-strands. When the sequence surrounding the DCCD site was compared to those surrounding the DCCD-reactive residue of other membrane proteins, no homology was apparent.
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PMID:Location of the dicyclohexylcarbodiimide-reactive glutamate residue in the bovine heart mitochondrial porin. 768 55

Mitochondria from malignant tumor cell lines show a higher capability for hexokinase binding than those from normal liver. To explore possible differences in hexokinase binding sites of mitochondria between tumor cells and normal liver, we characterized porin isoforms expressed in tumor cells. Cloning experiments on the three porin isoforms, VDAC1, VDAC2 and VDAC3 from malignant tumor cell line AH130 clearly showed that their primary structures were completely identical to those of the corresponding VDACs of normal liver cells. Possible expression of the fourth porin isoform in AH130 cells was excluded by degenerate primer-based RT-PCR. However, the transcript levels of the three VDAC isoforms in AH130 cells were significantly higher than those in normal liver. These results suggest that the high hexokinase-binding capability of malignant tumor cell mitochondria was not due to any structural difference, but due to a quantitative difference in binding sites.
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PMID:Characterization of porin isoforms expressed in tumor cells. 1099 68

The outer mitochondrial membrane pore (VDAC) changes its structure either voltage-dependently in artificial membranes or physiologically by interaction with the adenine nucleotide translocase (ANT) in the c-conformation. This interaction creates contact sites and leads in addition to a specific organisation of cytochrome c in the VDAC-ANT complexes. The VDAC structure that is specific for contact sites generates a signal at the surface for several proteins in the cytosol to bind with high capacity, such as hexokinase, glycerol kinase and Bax. If the VDAC binding site is not occupied by hexokinase, the VDAC-ANT complex has two critical qualities: firstly, Bax gets access to cytochrome c and secondly the ANT is set in its c-conformation that easily changes conformation into an unspecific channel (uniporter) causing permeability transition. Activity of bound hexokinase protects against both, it hinders Bax binding and employs the ANT as anti-porter. The octamer of mitochondrial creatine kinase binds to VDAC from the inner surface of the outer membrane. This firstly restrains interaction between VDAC and ANT and secondly changes the VDAC structure into low affinity for hexokinase and Bax. Cytochrome c in the creatine kinase complex will be differently organised, not accessible to Bax and the ANT is run as anti-porter by the active creatine kinase octamer. However, when, for example, free radicals cause dissociation of the octamer, VDAC interacts with the ANT with the same results as described above: Bax-dependent cytochrome c release and risk of permeability transition pore opening.
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PMID:The function of complexes between the outer mitochondrial membrane pore (VDAC) and the adenine nucleotide translocase in regulation of energy metabolism and apoptosis. 1283 65

In tumour cells, elevated levels of mitochondria-bound isoforms of hexokinase (HK-I and HK-II) result in the evasion of apoptosis, thereby allowing the cells to continue proliferating. The molecular mechanisms by which bound HK promotes cell survival are not yet fully understood. Our studies relying on the purified mitochondrial outer membrane protein VDAC (voltage-dependent anion channel), isolated mitochondria or cells in culture suggested that the anti-apoptotic activity of HK-I occurs via modulation of the mitochondrial phase of apoptosis. In the present paper, a direct interaction of HK-I with bilayer-reconstituted purified VDAC, inducing channel closure, is demonstrated for the first time. Moreover, HK-I prevented the Ca(2+)-dependent opening of the mitochondrial PTP (permeability transition pore) and release of the pro-apoptotic protein cytochrome c. The effects of HK-I on VDAC activity and PTP opening were prevented by the HK reaction product glucose 6-phosphate, a metabolic intermediate in most biosynthetic pathways. Furthermore, glucose 6-phosphate re-opened both the VDAC and the PTP closed by HK-I. The HK-I-mediated effects on VDAC and PTP were not observed using either yeast HK or HK-I lacking the N-terminal hydrophobic peptide responsible for binding to mitochondria, or in the presence of an antibody specific for the N-terminus of HK-I. Finally, HK-I overexpression in leukaemia-derived U-937 or vascular smooth muscle cells protected against staurosporine-induced apoptosis, with a decrease of up to 70% in cell death. These results offer insight into the mechanisms by which bound HK promotes tumour cell survival, and suggests that its overexpression not only ensures supplies of energy and phosphometabolites, but also reflects an anti-apoptotic defence mechanism.
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PMID:In self-defence: hexokinase promotes voltage-dependent anion channel closure and prevents mitochondria-mediated apoptotic cell death. 1456 Dec 15

The mechanism of Bax-dependent cytochrome c release is still controversial and may also depend on the actual localisation of cytochrome C: (i) we studied the distribution of cytochrome c in sub-fractions of rat kidney mitochondria and found that 10-20% of the total cytochrome c was associated at the peripheral inner membrane and to some extent organised in the contact sites. (ii) Cytochrome c concentrations in the contact site fractions varied related to surface bound hexokinase activity. It decreased upon reduction of contact sites by glycerol or specific dissociation of the VDAC-ANT complexes by bongkrekate, whereas it increased upon induction of contacts by dextran or association of VDAC-ANT complexes by atractyloside. (iii) The outer membrane pore (VDAC) acquires high capacity for hexokinase binding by interacting with the ANT. Thus, surface-attached hexokinase protein indicated the frequency of VDAC-ANT complexes and the correlation between hexokinase activity and cytochrome c suggested association of the latter to the complexes. (iv) Substances affecting exclusively the structure of either hexokinase (glucose-6P) or cytochrome c (borate) led to a decrease only of the effected protein without changing the concentration of other contact site constituents. (v) Hexokinase was furthermore used as a tool to isolate the contact site forming complex of outer membrane VDAC and inner membrane ANT from Triton-dissolved membranes. Cytochrome c remained attached to the hexokinase VDAC-ANT complexes that were reconstituted in phospholipid vesicles. (vi) The vesicles were loaded with malate and BaxDeltaC released the endogenous cytochrome c from the reconstituted complexes without forming unspecific pores for malate. BaxDeltaC targeted a cytochrome c fraction associated at the VDAC-ANT complex. The cytochrome c organisation was dependent on the actual structure of VDAC and ANT. Thus, the BaxDeltaC effect was suppressed either by hexokinase utilising glucose and ATP or by bongkrekic acid both influencing the pore and ANT structure.
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PMID:The intra-mitochondrial cytochrome c distribution varies correlated to the formation of a complex between VDAC and the adenine nucleotide translocase: this affects Bax-dependent cytochrome c release. 1474 42

In thymocytes, dexamethasone initiates cytochrome c-dependent processing of caspase-9 and the activation of caspase-3 to trigger apoptotic damage. Using murine thymocytes or a thymocyte cell line WEHI 7.1, we show that this pathway is inhibited by dominant-negative caspase-9, the anti-apoptotic protein Bcl-2, or by blocking components of the mitochondrial permeability transition pore complex (PTPC). We use DIDS (dithiocyanatostilbene-2,2-disulfonic acid), a pharmacological modifier of VDAC (voltage-dependent anion channel) function or ectopic expression of hexokinase-II, to examine the role of the VDAC--a mitochondrial outer membrane protein--in this apoptotic pathway. This approach implicated the VDAC in dexamethasone-mediated cytochrome c release, processing of caspase-9 and caspase-3, the loss of mitochondrial transmembrane potential (Deltapsim), nuclear damage and cell lysis. Inhibiting the adenine nucleotide transporter (ANT), a protein on the mitochondrial inner membrane, also blocks dexamethasone-induced apoptosis, but the ANT regulates caspase-3 processing and nuclear damage but not the mitochondrial efflux of cytochrome c. Collectively, the data identify two separable, but connected events in dexamethasone-induced mitochondrial damage in thymocytes. The first event is an increase in permeability of the mitochondrial outer membrane leading to VDAC-regulated efflux of cytochrome c and initial processing of caspase-9 followed by ANT-dependent caspase-3 processing and apoptotic damage to cells.
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PMID:The mitochondrial phase of the glucocorticoid-induced apoptotic response in thymocytes comprises sequential activation of adenine nucleotide transporter (ANT)-independent and ANT-dependent events. 1497 Oct 37

VDAC changes its structure either voltage dependent in artificial membranes or physiologically by interaction with the c conformation of the adenine nucleotide translocator (ANT). This interaction creates contact sites and leads to a specific organisation of cytochrome c in the VDAC ANT complexes. The VDAC structure specific for contact sites thus generates a signal at the surface for several proteins in the cytosol to bind with high affinity such as hexokinase, glycerolkinase and Bax. If the VDAC binding site is not occupied by hexokinase, the VDAC ANT complex has two critical qualities: firstly, external Bax gets access to the cytochrome c and secondly the ANT stays in the c conformation that easily changes the structure to an unspecific uni-porter causing permeability transition. Activity of bound hexokinase protects against both, it hinders Bax binding and employs the ANT as specific anti-porter. The octamer of mitochondrial creatine kinase binds to VDAC from the inner surface of the outer membrane. This firstly hinders direct interaction between VDAC and ANT and secondly changes porin structure into low affinity for hexokinase and external Bax. Cytochrome c in the creatine kinase complex will be differently organised not accessible to Bax and the ANT is run as anti-porter by the active octamer. However, when free radicals cause dissociation of the octamer, VDAC interacts with the ANT with the same results as described above: Bax dependent cytochrome c release and risk of permeability transition pore opening.
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PMID:VDAC and peripheral channelling complexes in health and disease. 1497 75


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