Stimulation of brain hexokinase gene expression by recombinant brain insulin-like growth factor in C6 glial cells.

Glycolysis is essential for cerebral energy generation. Hence, expression and regulation of gene-encoding brain hexokinase (HK I), the exclusive brain glucose phosphorylating enzyme, can be a critical step in this process. The present study demonstrates the ability of recombinant brain insulin-like growth factor (BIGF, a closely related member of insulin superfamily) to stimulate HK I gene expression in a concentration- and time-dependent manner in C6 glial cells.

Expression of cell surface glycoprotein CD44 and integrins in breast cancers among Indian women.

Parsis, the sole surviving group of followers of Zoroaster who are settled in Bombay, have a fourfold higher incidence of breast cancer than the general population of Greater Bombay. CD44 expression was studied by immunohistochemistry in breast cancers of 50 non-Parsi and 35 Parsi women, 10 normal breast tissues, 10 proliferative lesions and 49 tissues adjoining a tumor mass. Alpha2 and beta1 integrins could be studied in only 42 malignant cases and five normal tissues.

Expression of two type II-like tumor hexokinase RNA transcripts in cancer cell lines.

To maintain an elevated glycolytic rate, cancerous or proliferating cells alter the expression pattern of rate limiting glycolytic enzymes. Since glucose phosphorylation is the first step in glycolysis, hexokinase (HK), the first rate limiting glycolytic enzyme, can play a key regulatory role in this process. A low-Km, mitochondrial type II-like tumor HK is described as the predominant form in hepatomas.

Insulin-like growth factor I induces tumor hexokinase RNA expression in cancer cells.

Increased glycolysis is a characteristic of cancer cells. Though less efficient in energy production, it ensures continuous supply of energy and phosphometabolites for biosynthesis enabling metastatic and less vascularized cancer cells to proliferate even under hypoxic conditions. Since hexokinase is the first rate limiting enzyme in the glycolytic pathway, elevated levels of Type II like hexokinase in tumors are of great significance in this context.

Mapping of glucose and glucose-6-phosphate binding sites on bovine brain hexokinase. A 1H- and 31P-NMR investigation.

Inhibition of bovine brain hexokinase by its product, glucose 6-phosphate, is considered to be a major regulatory step in controlling the glycolytic flux in the brain. Investigations on the molecular basis of this regulation, i.e.

Brain hexokinase has no preexisting allosteric site for glucose 6-phosphate.

Difference spectroscopic investigations on the interaction of brain hexokinase with glucose and glucose 6-phosphate (Glc-6-P) show that the binary complexes E-glucose and E-Glc-6-P give very similar UV difference spectra. However, the spectrum of the ternary E-glucose-Glc-6-P complex differs markedly from the spectra of the binary complexes, but resembles that produced by the E-glucose-Pi complex. Direct binding studies of the interaction of Glc-6-P with brain hexokinase detect only a single high-affinity binding site for Glc-6-P (KD = 2.

Magnetic resonance studies on the interaction of metal-ion and nucleotide ligands with brain hexokinase.

Our previous studies have shown that one manganous ion binds tightly to bovine hexokinase, with a Kd = 25 +/- 4 microM. The characteristic proton relaxation rate (PRR) enhancement of this binary complex (epsilon b) is 3.5 at 9 MHz and 23 degrees C [Jarori, G.

Reaction of brain hexokinase with a substrate-like reagent. Alkylation of a single thiol at the active site.

An analogue of the substrate glucose, N-(bromoacetyl)-D-glucosamine (GlcNBrAc) inactivates bovine brain mitochondrial hexokinase completely and irreversibly in a pseudo-first-order fashion at pH 8.5 and 22 degrees C. The rate of inactivation of hexokinase by this reagent does not increase linearly with increasing reagent concentration but exhibits an apparent saturation effect, suggesting the formation of a reversible complex between the enzyme and the reagent prior to the inactivation step.

Effect of ligands on the reactivity of essential sulfhydryls in brain hexokinase. Possible interaction between substrate binding sites.

Inactivation of bovine brain mitochondrial hexokinase by 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), a sulfhydryl specific reagent, has been investigated. The study shows that the inactivation of the enzyme by DTNB proceeds by way of prior binding of the reagent to the enzyme and involves the reaction of 1 mol of DTNB with a mol of enzyme. At stoichiometric levels of DTNB, the inactivation of the enzyme is accompanied by the formation of a disulfide bond.