Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies from this laboratory have shown that mitochondrial bound hexokinase is markedly elevated in highly glycolytic hepatoma cells (Parry, D. M., and Pedersen, P.L. (1983) J. Biol. Chem. 258, 10904-10912). A pore-forming protein, porin, within the outer membrane appears to comprise at least part of the receptor site (Nakashima, R.A., Mangan, P.S., Colombini, M., and Pedersen, P.L. (1986). Biochemistry 25, 1015-1021). In studies reported here experiments were carried out to assess the functional significance of mitochondrial bound tumor hexokinase. Two approaches were used to determine whether the bound enzyme has preferred access to mitochondrially generated ATP relative to cytosolic ATP. The first approach compared the time course of glucose 6-phosphate formation by AS-30D hepatoma mitochondria under conditions where ATP was regenerated endogenously via oxidative phosphorylation or exogenously by added pyruvate kinase and phosphoenolpyruvate. The second approach involved the measurement of the specific radioactivity of glucose 6-phosphate formed following the addition of [gamma-32P]ATP to either phosphorylating or nonphosphorylating AS-30D mitochondria. Both approaches provided results which show that the source of ATP for bound hexokinase is derived preferentially from the ATP synthase residing within the inner mitochondrial membrane compartment rather than from the medium (i.e. from the cytosolic compartment). These results provide the first direct demonstration that the exceptionally high level of hexokinase bound to mitochondria of highly glycolytic tumor cells has preferred access to mitochondrially generated ATP, a finding that may have rather profound metabolic significance for such tumors.
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PMID:Functional significance of mitochondrial bound hexokinase in tumor cell metabolism. Evidence for preferential phosphorylation of glucose by intramitochondrially generated ATP. 318 54

Recent studies from this laboratory have demonstrated that a form of hexokinase characteristic of rapidly growing, highly glycolytic tumor cells is bound to an outer mitochondrial membrane receptor complex containing a Mr 35,000 pore protein (D. M. Parry and P. L. Pedersen, J. Biol. Chem., 258: 10904-10912, 1983; R. A. Nakashima, et al., Biochemistry, 25: 1015-1021, 1986). In new studies reported here the specificity of this receptor complex for binding hexokinase is defined, and a purification scheme is described which leads to a homogeneous and bindable form of the tumor hexokinase. In the AS-30D hepatoma, hexokinase activity is elevated more than 100-fold relative to liver tissue. The relative increase in hexokinase activity is 8 times greater than that of any other glycolytic enzyme. Hexokinase is the only glycolytic enzyme of AS-30D cells to exhibit a mitochondrial/cytoplasmic specific activity ratio greater than 1, showing a 3.5-fold elevation in the mitochondrial fraction. 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. The final fraction has a specific activity of 144 units per mg of protein, with a Km for glucose of 0.13 mM and for ATP of 1.4 mM. The purified tumor enzyme migrates as a single species upon sodium dodecyl sulfate: polyacrylamide gel electrophoresis with an apparent molecular weight of 98,000. Significantly, the purified tumor enzyme retains its activity for mitochondrial binding. Additional results derived from chromatographic, polyclonal antibody, and amino acid analysis studies indicate that the predominant rat hepatoma hexokinase species is related most closely to isozymic form(s) of the enzyme commonly referred to as type II, and least related to the liver type IV isozyme (glucokinase).
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PMID:Purification and characterization of a bindable form of mitochondrial bound hexokinase from the highly glycolytic AS-30D rat hepatoma cell line. 333 84

Automated Edman degradation of seven purified tryptic peptides from Novikoff hepatoma hexokinase C revealed amino acid sequences that could be easily aligned within the primary structure of yeast hexokinases. This high degree of structural homology suggests a common evolutionary origin for mammalian and yeast hexokinases. Some of the sequenced peptides overlapped with each other, as well as with regions of the sequence of yeast hexokinases, suggesting that during evolution the 100,000 molecular weight subunit mammalian hexokinases may have resulted from gene duplication followed by gene fusion from a pre-vertebrate 50,000 molecular weight hexokinase ancestor.
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PMID:Amino acid sequence homology between yeast hexokinases and rat hexokinase C. 353 66

The purification to homogeneity of hexokinases B and C from the cytosol of rat Novikoff hepatoma was achieved by a protocol using an initial chromatography on Blue 2-agarose to separate the isoenzymes from each other. After that step each hexokinase was subjected to chromatography on DEAE-cellulose, hydroxyapatite and Sephacryl S-300, followed by re-chromatography on hydroxyapatite. The final preparations of hexokinases B and C had specific activities of 86 and 23.5 units/mg of protein respectively, and gave single bands on electrophoresis under non-denaturing conditions or in SDS/polyacrylamide gels. Mr values of about 100,000 were found for both isoenzymes either by Sephacryl S-300 chromatography or by SDS/polyacrylamide-gel electrophoresis. Values of apparent Km for glucose and ATP of pure hexokinase B were similar to those reported for the enzyme from other sources. The apparent Km value for glucose of hexokinase C was 0.025 mM. Marked inhibition of hexokinase C by glucose concentrations above 0.2 mM was found. The effect was partially relieved by ATP concentrations above 1 mM and was independent of pH. Glucose 6-phosphate was inhibitory, but the Ki value (0.18 mM) is higher than those reported for other animal hexokinases. The amino acid composition of hexokinase C was found to be similar to those reported for hexokinases B and D. Also, an immune serum directed against hexokinase A was able, at low dilutions, to bind hexokinases B and C. An immune serum directed against hexokinase C was able, at low dilutions, to bind hexokinase B and also, but weakly, hexokinase A.
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PMID:Hexokinase isoenzymes from the Novikoff hepatoma. Purification, kinetic and structural characterization, with emphasis on hexokinase C. 359 83

Essential differences are established between the activities in enzymes of monophosphohexoses' transformation in the Zajdela hepatoma and liver of tumour-bearing rats. So, a very low hexokinase activity is observed in the liver, the activity of phosphoglucomutase and glucose-6-phosphate being high. In hepatoma cells the activity of hexokinase is relatively high and that of phosphoglucomutase, glucose-6-phosphate phosphatase and dehydrogenases--glucose-6-phosphate and 6-phosphogluconate inhibiting the activity of phosphoglucomutase is considerably lower. Significant differences are also found in the ratios of the glucose, glucose-6-phosphate, fructose and fructose-6-phosphate concentrations, that evidences for changes in the regulatory mechanisms in the hepatoma cells.
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PMID:[Characteristics of hexosephosphate transformation regulation in Zajdela hepatoma and the liver of tumor-bearing rats]. 381 Aug 99

The level of hexokinase-specific mRNA in rat liver and in rat ascites hepatoma (Zajdela) was assessed by translating free polysomes from both cell types in a reticulocyte lysate. Translation of hexokinase occurred with approximately a 10 fold higher frequency in tumor cells than in liver, suggesting that transcriptional activation is in part responsible for increased levels of hexokinase in tumor.
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PMID:Evidence that transcription of the hexokinase gene is increased in a rapidly growing rat hepatoma. 408 89

The contents of mitochondrial inner membrane protein complexes were compared in normal liver and in Zajdela hepatoma mitochondria by the immunotransfer technique. Antibodies against core proteins 1 and 2, cytochrome c1, the iron-sulfur protein of Complex III, subunits I and II of cytochrome oxidase, and the alpha and beta subunits of the F1-ATPase were used. In addition, antibodies against a primary dehydrogenase, beta-hydroxybutyrate dehydrogenase, as well as the outer membrane pore protein were used. The results indicate that the components of the cytochrome chain and porin are greatly enriched in hepatoma mitochondria compared to normal rat liver mitochondria. This enrichment was also reflected in the rates of respiration in tumor mitochondria using a variety of substrates. Enrichment of porin may partially account for increased hexokinase binding to tumor mitochondria. In contrast to the respiratory chain components, the F1-ATPase and F0 (measured by DCCD binding) were not increased in tumor mitochondria. Thus, Zajdela hepatoma mitochondria components are nonstoichiometric, being enriched in oxidative capacity but relatively deficient in ATP synthesizing capacity. Finally, beta-hydroxybutyrate dehydrogenase, which is often decreased in hepatoma mitochondria, was shown here by immunological methods to be decreased by only 40%, whereas enzyme activity was less than 5% of that in normal rat liver.
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PMID:Immunochemical analysis of the membrane proteins of rat liver and Zajdela hepatoma mitochondria. 609 64

Inhibition of IMP dehydrogenase in AS-30D hepatoma cells in suspension culture resulted in a pronounced and selective reduction of guanine nucleotide pools. Total acid-soluble guanine nucleotides decreased to 40% and the content of GTP and GDP dropped to about 20% of control within 4 h when mycophenolate or ribavirin were used as the inhibitors. Induction of GTP deficiency was associated with a 50% rise in UTP and other uracil nucleotides. Guanosine rapidly reversed both the reduction of guanine nucleotide pools and the elevation of cellular UTP contents. Enzymatic nucleotide analyses in cell and tissue extracts after treatment with ribavirin indicated that ribavirin 5'-triphosphate was an effective substrate for yeast hexokinase, yeast phosphoglycerate kinase, and nucleosidediphosphate kinase from yeast or bovine liver. These results were confirmed in detail by the use of synthetic ribavirin 5'-triphosphate and 5'-diphosphate. The latter nucleotide analog was also a substrate of pyruvate kinase from muscle. Mycophenolate-induced GTP deficiency was associated with an arrest of hepatoma cell growth in suspension culture. Ribavirin, at an equimolar concentration, was much less effective in this respect. None of the two inhibitors had a detectable effect, however, in vivo when guanine or uracil nucleotides were assayed in liver. This indicated that an inhibition of de novo guanylate synthesis in vivo can be compensated by salvage pathway synthesis.
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PMID:Selective guanosine phosphate deficiency in hepatoma cells induced by inhibitors of IMP dehydrogenase. 610 11

Mitochondria were isolated from whole homogenates of normal liver and Novikoff hepatomas using reorienting rate zonal centrifugation on sucrose gradients. The activities of several mitochondrial-specific enzymes and ultrastructure were compared in the two tissues. Our results indicate that cytochrome oxidase, lipoamide dehydrogenase, malate dehydrogenase, and succinate dehydrogenase activities are all higher in liver homogenates than in Novikoff hepatoma homogenates. Mitochondrial hexokinase, however, is much greater in the hepatoma than in liver. The activity of these enzymes in isolated mitochondria displayed a much different pattern. Both cytochrome oxidase and succinate dehydrogenase activities were higher in hepatoma mitochondria than in liver mitochondria. Lipoamide dehydrogenase and malate dehydrogenase, conversely, were higher in liver mitochondria. Hexokinase was found to be virtually absent in liver mitochondria but plentiful in hepatoma mitochondria. Ultrastructural studies have shown that the hepatoma mitochondria are much smaller in size, which results in a decreased rate of migration into the gradient. These studies have also shown that normal liver consists of predominantly "condensed" forms of mitochondria, whereas hepatoma contained a majority of "twisted" species. Experiments using 1% bovine serum albumin in the homogenization procedures and in the gradient have confirmed earlier observations that bovine serum albumin is essential for optimal isolation of neoplastic mitochondria.
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PMID:Characteristics of mitochondria isolated by rate zonal centrifugation from normal liver and Novikoff hepatomas. 624 94

The activities of key enzymes of glycolysis and of the glucose shunt as well as the capacity of lactic acid formation were determined in the high-speed tissue supernatant of the transplantable Albert hepatoma of mouse [originally produced by oral application of chrysoidin (2,4-diaminoazobenzene) on C57 Black mice]. Furthermore, the particle-bound hexokinase activity was determined. The following results were obtained: In the hepatoma the activities of aldolase, pyruvate kinase and lactic dehydrogenase are hardly altered compared with normal liver. The activities of hexokinase and phosphofructokinase are increased 2,5-fold, those of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase 2-fold. The capacity for lactic acid formation from glucose is 7 times as high in the hepatoma supernatant. Strong differences emerge from the liver-to-hepatoma relationship in terms of intracellular distribution of the hexokinase (total homogenate 1 : 5, supernatant 1 : 2,5 and particle-bound hexokinase activity 1 : 18). A summarizing consideration of all the results obtained so far for the Albert hepatoma shows that this malignoma departss in several biochemical parameters from the "Molecular Correlation Concept" maintained by Weber, providing more evidence for the individuality of tumors.
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PMID:[Activities of several enzymes of glycolysis and of the glucose shunt in the Albert hepatoma of mouse (author's transl)]. 625 66


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