Disease relevance of Hk1

• Extensive similarity in sequence, taken to indicate similarity in secondary and tertiary structure, is seen between the mammalian enzyme and yeast hexokinase isozymes A and B. All residues critical for binding glucose to the yeast enzyme are conserved in brain hexokinase [1].
• Therefore, in order to examine a possible link between increased glucose metabolism and the development of diabetic nephropathy mRNA and protein expression as well as enzyme activity of type 1 hexokinase were examined in kidneys of control and diabetic rats and in mesangial cells [2].
• Targeting of hexokinase 1 to liver and hepatoma mitochondria [3].
• Neither ischemia nor reperfusion affected the kinetic properties of hexokinase [4].
• A comparable anomeric behavior of hexokinase was observed in breast cancer (MCF-7) and lymphocytic leukemia (P388) cells [5].

Psychiatry related information on Hk1

• To understand this mechanism, it was hypothesized that the enzymes involved in the metabolism of glucose, viz. hexokinase and glucose-6-phosphatase, are affected by REM sleep deprivation [6].
• Hexokinase showed no variation with increasing periods of food deprivation [7].
• 5. Minimal nonsignificant changes were noted in the hexokinase activity of the hearts of all T groups (P greater than or equal to 0.05) [8].

High impact information on Hk1

• Second, the antiapoptotic activity of Akt requires only the first committed step of glucose metabolism catalyzed by hexokinase [9].
• Inhibition of early apoptotic events by Akt/PKB is dependent on the first committed step of glycolysis and mitochondrial hexokinase [9].
• We therefore propose that Akt increases coupling of glucose metabolism to oxidative phosphorylation and regulates PT pore opening via the promotion of hexokinase-VDAC interaction at the outer mitochondrial membrane [9].
• Finally, ectopic hexokinase expression mimics the ability of Akt to inhibit cytochrome c release and apoptosis [9].
• Here, we provide genetic evidence that Akt is required to maintain hexokinase association with mitochondria [10].

Chemical compound and disease context of Hk1

• 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 [11].
• In order to establish whether growth of glioma cells is associated with glucose transport and metabolism, we investigated expression of the glucose transporter and hexokinase, as well as glucose transport and glucose phosphorylation in rat C6 glioma cells growing at different rates [12].
• Effect of prenatally-induced and postnatally-maintained ketosis on beta-hydroxybutyrate dehydrogenase and hexokinase levels in the developing rat brain [13].
• The effects of hypo- and hyperthyroidism on total cerebellar hexokinase levels are interpreted in terms of the effect of thyroid hormone on the biochemical maturation of synaptic structures rich in hexokinase [14].
• Enzyme activities of hexokinase, phosphofructokinase and pyruvate kinase were not inhibited, but rather increased slightly after cerebral embolism [15].

Biological context of Hk1

• The structures define the glucose and G6P binding sites in these enzymes, suggest the mechanisms of intradomain G6P inhibition and activity loss in the Type I hexokinase N-terminal half, and reveal the structure of the membrane targeting motif that integrates the Type I hexokinase into the outer mitochondrial membrane [16].
• The complete amino acid sequence for the type I isozyme of hexokinase from rat brain has been deduced from the nucleotide sequence of cloned cDNA [17].
• These results provide strong support for the view that the "catalytic domain" at the C-terminus of the mammalian Type I hexokinase shares a common ancestry with yeast hexokinase [18].
• High glucose induces type 1 hexokinase gene expression in isolated glomeruli of diabetic rats and in mesangial cells [2].
• Furthermore, glucose phosphorylation via low Km hexokinase was detected only in the high responsive beta-cell subpopulation [19].

Anatomical context of Hk1

• Selective proteolytic cleavage of porin protein was performed and peptides were assayed for their, effect on hexokinase I binding to isolated mitochondria [20].
• Preincubation of mitochondria with purified porin strongly increases hexokinase I binding to rat liver mitochondria [20].
• In addition, glomerular mesangial cells were incubated in high glucose medium and hexokinase expression determined along with enzyme activity [2].
• Surgical biopsies of liver from patients undergoing partial hepatectomies and parenchymal hepatocytes derived from the biopsies were used to assay glucokinase, hexokinase and phosphoenolpyruvate carboxykinase activities [21].
• These findings support the hypothesis that hexokinase is bound to mitochondria in rat brain astrocytes in vivo, and that this association is sensitive to cell metabolic state [22].

Associations of Hk1 with chemical compounds

• We have determined the structures of the glucose-6-phosphate (G6P)-inhibitable 100,000 Mr Type I hexokinase from rat and the G6P-sensitive 50,000 Mr hexokinase from Schistosoma mansoni at a resolution of 2.8 and 2.6 A respectively [16].
• An essential serine residue implicated in the binding of Glc to the yeast enzyme is also conserved in Peptide III from rat brain hexokinase [18].
• Specificity of DCCD-reactive domain binding to hexokinase I was demonstrated by competition of the peptides for porin binding sites on hexokinase as well as by blockage hexokinase binding by N,N-dicyclohexylcarbodiimide [20].
• The results also imply that the redistribution of hexokinase and the differential effect of insulin on its affinity for tracer and tracee are responsible for changes in the "lumped constant" (i.e., the correction factor used to equate 2-deoxyglucose to glucose uptake) [23].
• To test these hypotheses, we analyzed the subcellular distribution of hexokinase relative to mitochondria in paraformaldehyde-fixed astrocytes using immunocytochemistry and quantitative three-dimensional confocal microscopy [22].

Physical interactions of Hk1

• (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 [24].
• Despite normal to elevated hexokinase and glucokinase activities in the islets of these glucose-intolerant animals and despite normal mitochondrial binding of the hexokinase isoenzymes, the metabolic response to a high concentration of D-glucose is severely affected, especially in terms of D-[6-14C]glucose oxidation [25].
• Exogenous glycerol kinase competed effectively with mitochondrially bound hexokinase for extramitochondrial ATP, with relatively low levels of glycerol kinase completely inhibiting phosphorylation of Glc.(ABSTRACT TRUNCATED AT 400 WORDS)[26]
• The studies reveal that a significant fraction of the ADP generated by either adenylate kinase in the intermembrane space or by outer membrane bound hexokinase isozyme I, is not accessible to extramitochondrial pyruvate kinase [27].

Enzymatic interactions of Hk1

• Results suggested that glucosamine may be phosphorylated by high Km hexokinase, i.e. glucokinase [EC 2.7.1.2] [28].

Regulatory relationships of Hk1

• A reconstituted system prepared from RINm5F and HIT cell extracts exhibited a composite concentration-dependency curve of glucose usage and showed substantial inhibition of hexokinase and almost fully expressed glucokinase [29].
• Endothelin-1 stimulates the translocation and upregulation of both glucose transporter and hexokinase in astrocytes: relationship with gap junctional communication [30].
• The latter results are consistent with amylin and epinephrine stimulating glycogenolysis and inhibiting hexokinase activity by intracellular accumulation of glucose 6-phosphate [31].
• 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 [32].

Other interactions of Hk1

• These results provide direct support for the proposal that the mammalian hexokinases of approximately 100 kDa have evolved by a process of duplication and fusion of a gene encoding an ancestral hexokinase similar to the yeast enzyme of approximately 50 kDa [17].
• In this study, we have used recombinant adenoviruses to overexpress the liver and islet isoforms of glucokinase as well as low Km hexokinase I in isolated rat islets of Langerhans [33].
• Stimulation of brain hexokinase gene expression by recombinant brain insulin-like growth factor in C6 glial cells [34].
• The highly glucolytic hepatoma cell line H-91 is characterized by a high hexokinase activity to rat liver; 50% of this activity is associated with the mitochondrial fraction [Bustamante, E., & Pederson, P.L. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 3735--3739] [35].
• Furthermore, we have demonstrated that PACAP exerts long-term effects on beta-cells, such as transcriptional regulation of the insulin gene and genes of the glucose-sensing system (GLUT1 and hexokinase 1) [36].

Analytical, diagnostic and therapeutic context of Hk1

• In the present study, peptide mapping of hexokinase modified by radiolabeled GlcNBrAc yields three labeled peptides (Peptides I-III) [18].
• Modulation of hexokinase association with mitochondria analyzed with quantitative three-dimensional confocal microscopy [22].
• To test whether either protein controls the sensitivity of the beta cell to glucose by controlling the rate of glucose catabolism, we used gene-transfer techniques to express the isoenzymes glucose transporter 1 and hexokinase I in beta cells and measured the response to glucose of the insulin gene promoter [37].
• Purification of hexokinase is accomplished by preferential solubilization of the mitochondrial bound enzyme with glucose-6-phosphate, followed by high-performance liquid chromatography on gel permeation and anion exchange columns [38].
• Here we demonstrate by Southern blot analysis and fluorescence in situ hybridization (FISH) that in the rapidly growing rat AS-30D hepatoma cell line, enhanced hexokinase activity is associated with at least a 5-fold amplification of the type II gene relative to normal hepatocytes [39].

References