Red Blood Cell Hexokinase in Tumor Bearing Mice

Red blood cell hexokinase of tumor-bearing BALB/c mice was found to be 35% higher than in the normal controls, whereas glucose 6-phosphate-dehydrogenase and other red blood cell glycolytic enzymes were in the normal range. This hexokinase increase cannot be explained by a mean younger red cell population because normal hematological data and normal red cell enzymes, known as red cell age-markers, have been found in tumor-bearing mice. The isozymic pattern of red cell hexokinase is not modified in the tumor-bearing mice.

Adenine and Pyridine Nucleotides in the Red Blood Cells of Subjects with Solid Tumors

The concentration of adenine (ATP, ADP, AMP) and pyridine (NADP+, NADPH, NAD+, NADH) nucleotides in the erythrocytes of subjects affected by solid tumors was evaluated using a method which allows their simultaneous extraction and reverse-phase high-performance liquid chromatographic analysis. The results showed a lower level of ATP in the erythrocytes of subjects affected by solid tumors, whereas no significant modifications were observed in the other compounds. In fact, the mean value of ATP in these subjects was 27 % lower than that of normal adults. This fact is discussed in relation to other enzymatic and metabolic modifications previously observed in red blood cells.

Relationship between Erythrocyte Hexokinase in Cancer Patients and Red Cell Age

A study of hexokinase isozymic pattern and age dependence of the enzyme was carried out on erythrocytes of 4 patients with adenocarcinoma of the gastrointestinal tract. On the basis of our results, we think that the increase in hexokinase activity previously reported and the increase in both subtypes (Ia and Ib) of the enzyme herein described are not due to a mean younger red cell population caused by secondary anemia, which is frequently present in cancer patients.

Modification of the Hexokinase Activity in the Red Blood Cells of Subjects with Differentiated Adenocarcinoma

In the present work we found a significant increase of erythrocyte HK activity in subjects suffering from differentiated adenocarcinoma. Some erythrocyte enzymatic activities (such as HK, PK, G-6-PD, 6-PGD, PHI and GR) in the red blood cells of 96 subjects, of which 55 were healthy or with noncancerous pathology and 41 had malignant tumors, are considered. Evident modification was shown only for the HK, which together with PFK and PK are limiting steps of glycolysis.

Electronic nose and GC-MS analysis of volatile compounds in Tuber magnatum Pico: evaluation of different storage conditions

The characteristic aromatic composition of white truffles (Tuber magnatum Pico) determines its culinary and commercial value. However modifications of truffle organoleptic proprieties occur during preservation. A study of headspace of white truffles by using Electronic nose (E-nose), gas chromatography-mass spectrometry (GC-MS) and sensory analyses was performed. Truffles were stored at different conditions for 7 days: +4 and +8°C wrapped in blotting paper or covered by rice or none of the above. Headspace E-nose measurements and sensory analyses were performed each day. Statistical multivariate analysis of the data showed the capability of E-nose to predict sensorial analysis scores and to monitor aroma profile changes during storage. Truffle's volatile molecules were also extracted by headspace solid phase microextraction technique and separated and identified by GC-MS. Partial Components Analysis of data was performed. E-nose and GC-MS results were in agreement and showed that truffle storage in paper at +8°C seemed to be the best storage condition.

Characterization of Dermanyssus gallinae (Acarina: Dermanissydae) by sequence analysis of the ribosomal internal transcribed spacer regions

In the present work mites previously identified as Dermanyssus gallinae De Geer (Acari, Mesostigmata) using morphological keys were investigated by molecular tools. The complete internal transcribed spacer 1 (ITS1), 5.8S ribosomal DNA, and ITS2 region of the ribosomal DNA from mites were amplified and sequenced to examine the level of sequence variations and to explore the feasibility of using this region in the identification of this mite. Conserved primers located at the 3'end of 18S and at the 5'start of 28S rRNA genes were used first, and amplified fragments were sequenced. Sequence analyses showed no variation in 5.8S and ITS2 region while slight intraspecific variations involving substitutions as well as deletions concentrated in the ITS1 region. Based on the sequence analyses a nested PCR of the ITS2 region followed by RFLP analyses has been set up in the attempt to provide a rapid molecular diagnostic tool of D. gallinae.

Rhodiola rosea as antioxidant in red blood cells: ultrastructural and hemolytic behaviour

Rhodiola rosea L. (Crassulaceae) is a plant that lives at high altitude in Europe and Asia, widely used for its high capacity to increase the organism resistance to different stress conditions. Although a few international literature supports these effects, today R. rosea has become a common component of many dietary supplements also in the Western world. The aim of the present study was to investigate the effect of the R. rosea roots aqueous extract on in vitro human erythrocytes exposed to hypochlorous acid (HOCl)-oxidative stress. Several damages occur in human erythrocytes exposed in vitro to HOCl, among these membrane protein and lipid modifications, shifting from the discocyte shape to the echinocyte one, and determining lysis ultimately. Therefore, in the present work, the evaluation of the antioxidant capacity of the Rhodiola extract has been carried out by means of scanning electron microscopy and of hemolytic behaviour on human erythrocytes exposed to HOCl in the presence of increasing doses of the aqueous extract in different experimental environments (co-incubation and subsequent incubations). The results obtained are consistent with a significant protection of the extract in presence of the oxidative agent, but a cautionary note emerges from the analysis of the data related to the cell exposition to the plant extract in the absence of any induced oxidative stress. In fact, the addition to erythrocyte of high doses of R. rosea extract always determines severe alterations of the cell shape.

The wall paintings in the Oratorio of San Giovanni Battista in Urbino: a study finalized to a correct conservation project

The walls of the Oratorio of San Giovanni Battista in Urbino are decorated with outstanding mural paintings dating back to the 15th century. Due to degradation processes that have occurred in the past years, such paintings require a conservative restoration project. In order to evaluate reasons of the decay, some scientific studies have been performed. They consist of macroscopic observations and chemical (EDS), morphological (SEM) and mineralogical (XRD) analyses of samples both from the original preparatory layers under the painted layers and from the restored plasters at the surbase of the wall. In addition, environmental studies have been performed to verify microclimatic conditions of the church in which the mural paintings are located. Finally, a conservative restoration project was proposed.

Intracellular ascorbic acid enhances the DNA single-strand breakage and toxicity induced by peroxynitrite in U937 cells

A well-established protocol to increase the intracellular content of ascorbic acid was used to investigate the effects of the vitamin on DNA single-strand breakage and toxicity mediated by authentic peroxynitrite (ONOO(-)) in U937 cells. This protocol involved exposure for 60 min to 100 microM dehydroascorbic acid, which was taken up by the cells and converted into ascorbic acid via a GSH-independent mechanism. At the time of exposure to ONOO(-), which was performed in fresh saline immediately after loading with dehydroascorbic acid, the vitamin present in the cells was all in its reduced form. It was found that, in cells that are otherwise ascorbate-deficient, an increase in their ascorbic acid content does not prevent, but rather enhances, the DNA-damaging and lethal responses mediated by exogenous ONOO(-). These results therefore suggest that acute supplementation of ascorbic acid can be detrimental for individuals with pathologies associated with a decrease in ascorbic acid and in which ONOO(-) is known to promote deleterious effects.

Quercetin prevents glutathione depletion induced by dehydroascorbic acid in rabbit red blood cells

Exposure of rabbit red blood cells to dehydroascorbic acid (DHA) caused a significant decline in glutathione content which was largely prevented by quercetin, whereas it was insensitive to various antioxidants, iron chelators or scavengers of reactive oxygen species. This response was not mediated by chemical reduction of either extracellular DHA or intracellular glutathione disulfide. In addition, the flavonoid did not affect the uptake of DHA or its reduction to ascorbic acid. Rather, quercetin appeared to specifically stimulate downstream events promoting GSH formation.

In vitro effects of 50 Hz magnetic fields on oxidatively damaged rabbit red blood cells

The aim of this study was to investigate the effects of 50 Hz magnetic fields (0.2-0.5 mT) on rabbit red blood cells (RBCs) that were exposed simultaneously to the action of an oxygen radical-generating system, Fe(II)/ascorbate. Previous data obtained in our laboratory showed at the exposure of rabbit erythrocytes or reticulocytes to Fe(II)/ascorbate hexokinase inactivation, whereas the other glycolytic enzymes do not show any decay. We also observed depletion of reduced glutathione (GSH) content with a concomitant intracellular and extracellular increase in oxidized glutathione (GSSG) and a decrease in energy charge. In this work we investigated whether 50 Hz magnetic fields could influence the intracellular impairments that occur when erythrocytes or reticulocytes are exposed to this oxidant system, namely, inactivation of hexokinase activity, GSH depletion, a change in energy charge, and hemoglobin oxidation. The results obtained indicate the a 0.5 mT magnetic field had no effect on intact RBCs, whereas it increased the damage with Fe(II)/ascorbate to a 0.5 mT magnetic field induced a significant further decay in hexokinase activity (about 20%) as well as a twofold increase in methemoglobin production compared with RBCs that were exposed to the oxidant system alone. Although further studies will be needed to determine the physiological implications of these data, the results reported in this study demonstrate that the effects of the magnetic fields investigated are able to potentiate the cellular damage induced in vitro by oxidizing agents.

Quercetin prevents DNA single strand breakage and cytotoxicity caused by tert-butylhydroperoxide: free radical scavenging versus iron chelating mechanism

Although the antioxidant properties of flavonoids are well documented, it is still unclear whether these effects are dependent on radical scavenging or iron chelating activities. By using an experimental approach based on the notion that iron chelators suppress DNA strand scission and cytotoxicity caused by tert-butylhydroperoxide, whereas radical scavenging antioxidants prevent only the latter response, we provide experimental evidence indicating that the most prominent activity of the flavonoid quercetin resides in its ability to chelate iron. This experimental approach can be utilized for the assessment of iron chelation in the biological activity of flavonoids or other antioxidants.

Effect of 50 Hz sinusoidal electric and/or magnetic fields on the rate of repair of DNA single strand breaks in cultured mammalian cells exposed to three different carcinogens: methylmethane sulphonate, chromate and 254 nm U.V. radiation

Treatment of cultured mammalian cells with three different carcinogens, namely methylmethane sulphonate (MMS), chromate and 254 U.V. radiation, produces DNA single strand breaks (SSB) in cultured mammalian cells. The rate of removal of these lesions is not affected by exposure to 50 Hz electric (0.2 - 20 kV/m), magnetic (0.0002-0.2 mT), or combined electric and magnetic fields. These results indicate that, under the experimental conditions utilized in this study, 50 Hz electric, magnetic and electromagnetic fields (over a wide range of intensities) do not affect the machinery involved in the repair of DNA SSBs generated by different carcinogens in three different cultured mammalian cell lines, making it unlikely that field exposure enhances the ability of these carcinogens to induce transformation via inhibition of DNA repair.

Purification and characterization of the carboxyl-domain of human hexokinase type III expressed as fusion protein

In mammalian tissues hexokinase (ATP:D-hexose 6-phosphotransferase, EC 2.7.1.1) exists as four isoenzymes encoded by distinct genes. These proteins are homologous and are organized in two homologous domains, with the exception of hexokinase type IV which has only one. This organization is believed to be the result of a duplication and tandem fusion event involving the gene encoding for the ancestral hexokinase. In this study, we cloned the carboxyl-domain of human hexokinase type III and expressed it in Escherichia coli as a glutathione S-transferase fusion protein, using the pGEX-2T expression vector. The recombinant protein showed catalytic activity. A comparative study of the kinetic properties of the expressed carboxyl-domain and the enzyme partially purified from human lymphocytes is also shown. The results now allow a better understanding of the role of the carboxyl-domain in determining the catalytic properties of the enzyme.

The effect of 50 Hz sinusoidal electric and/or magnetic fields on the rate of repair of DNA single/double strand breaks in oxidatively injured cells

Exposure of cultured mammalian cells to 50 Hz electric (0.2-20 kV/m), magnetic (0.002-2 G), or combined electric and magnetic fields did not affect the rate of repair of DNA single strand breaks (SSB) induced by hydrogen peroxide. The same lack of effect was observed on the repair of both DNA SSBs and DNA double strand breaks (DSBs) in cells treated with the cocktail hydrogen peroxide/L-Histidine. These results indicate that exposure to electric and/or magnetic fields does not affect the machinery involved in the repair of DNA lesions in oxidatively injured cells thus suggesting that it is unlikely that field exposure might induce changes in the response of the cells to the tumor promoting or carcinogenic effects elicited by reactive oxygen species.

Mitochondria-bound hexokinase from rabbit reticulocytes is resistant to the inactivation induced by Fe(II)/ascorbate

Exposure of rabbit reticulocytes to Fe(II)/ascorbate induced a pronounced decay in hexokinase activity. In reticulocytes, this enzyme is present in at least three different molecular forms, Ia, Ia* and Ib, sub-types of hexokinase type I, which show different intracellular distribution. Hexokinase Ia and Ib are soluble, whereas hexokinase Ia* is almost entirely bound to the mitochondria. Anion exchange chromatography of hexokinase from intact reticulocytes exposed to Fe(II)/ascorbate revealed a selective inactivation of forms Ia and Ib, whereas the form Ia* did not show any decay. Binding to the mitochondrial membrane seems to be responsible for the observed resistance of the form Ia* to the inactivation elicited by Fe(II)/ascorbate. Indeed, by using a cell-free system in which hexokinase Ia* was solubilized using Triton X-100, the decay in hexokinase activity induced by iron/ascorbate involved all three enzymatic forms.

High resolution of multiple forms of rabbit reticulocyte hexokinase type I by hydrophobic interaction chromatography

Hydrophobic interaction chromatography (HIC) has been employed extensively in the separation of proteins by elution using a descending salt gradient, with and without the use of detergents or denaturing agents. In this study, a new hydrophobic interaction chromatographic support, Toyopearl Phenyl 650 S, was investigated in order to examine the distribution of multiple forms of rabbit reticulocyte hexokinase type I. These distinct forms of the enzyme, designated hexokinase Ia, Ia* and Ib, show similar kinetic and physical properties, similar molecular masses (ca. 100,000) and a different intracellular distribution. The results obtained using Toyopearl Phenyl 650 S of 20-50-microns particle diameter show that this HIC support allows very high resolution, comparable to that obtainable with HIC-HPLC columns but with the advantage of charging a higher amount of starting material even with a high protein concentration. These characteristics render Toyopearl Phenyl 650 S suitable for analytical and preparative purposes. Further, in the separation of multiple forms of rabbit reticulocyte hexokinase, the HIC method was shown to be superior to RP-HPLC, making possible the efficient separation of proteins with high molecular mass and their recovery in active forms. The Toyopearl Phenyl 650 S column was also shown to be more efficient than the ion-exchange chromatographic media previously used, allowing a quicker analysis of the multiple forms of rabbit reticulocyte hexokinase under different biological conditions.

Inactivation of rabbit red blood cell hexokinase activity promoted in vitro by an oxygen-radical-generating system

Rabbit red blood cell hexokinase (EC 2.7.1.1) has been shown to be inactivated in vitro by incubating intact erythrocytes in the presence of an oxygen-radical-generating system represented by ascorbate and iron. It was interesting to note that among the glycolytic enzymes, only hexokinase was found to be susceptible to the action of oxygen radicals, suggesting that the loss of activity of this enzyme may be one of the first signals of cellular damage in rabbit red blood cells. This statement is supported by the fact that, under the experimental conditions used, we did not observe any significant plasma membrane lipid peroxidation nor intracellular proteolysis. Furthermore, mature erythrocytes are unable to synthesize hexokinase as well as other proteins de novo; therefore, the inactivation of this enzyme, which is both the first and one of the rate-limiting enzymes of the glycolytic pathway, could play an important role in determining metabolic impairment of red blood cells, with possible physiological implications. We also investigated the effect of various radical scavengers and antioxidants (glucose, vitamin E, dithiothreitol, flavonoids) which are able to influence the inactivation of hexokinase activity to different extents. Finally, under the experimental conditions used (90 min of incubation at 37 degrees C), we did not observe any difference in the hemolysis of rabbit red blood cells incubated in the presence or absence of ascorbate and iron (hemolysis was about 1% after 90 min of incubation), suggesting that the system used was able to furnish information about the cellular damage produced by oxygen radicals without provoking cell lysis.

Studies on the possible biological effects of 50 Hz electric and/or magnetic fields: evaluation of some glycolytic enzymes, glycolytic flux, energy and oxido-reductive potentials in human erythrocytes exposed in vitro to power frequency fields

An attempt has been made to understand whether 50 Hz electric and magnetic fields (EMFs) are involved in producing bioeffects by exposing human erythrocytes in vitro. The study evaluated some key glycolytic enzymes, glucose consumption, lactate production, energy charge, 2,3-diphosphoglycerate, and reduced glutathione levels, all of which are biochemical parameters significant to erythrocyte function. Cells exposed to individual or superimposed EMFs have not shown any significant difference compared with the controls.

Electric and/or magnetic field effects on DNA structure and function in cultured human cells

Exposure of cultured K562 cells to 50 Hz electric (0.2-20 kV/m), magnetic (0.002-2 G), or combined electric and magnetic fields for up to 24 h did not result in the production of detectable DNA lesions, as assayed by the filter elution technique. The rate of cell growth was also unaffected as well as the intracellular ATP and NAD+ levels. These results indicate that, under the experimental conditions utilized in this study, 50 Hz electric, magnetic and electromagnetic fields are not geno- and cyto-toxic in cultured mammalian cells.

Preparative purification of pig red blood cell hexokinase type III using a new efficient chromatographic support

In this paper we report the purification of pig erythrocyte hexokinase type III, at preparative level, using 52 liters of starting material (hemolysate). This was possible using a new efficient anion exchanger support, the Toyopearl DEAE 650 M which allows completely to change the strategy of removing hemoglobin from hemolysates, permitting to handle large amounts of starting material and reducing work would have required months using conventional anion exchanger supports, to only 2-3 days. Furthermore, we have tested the binding of other red blood cell enzymes to the Toyopearl DEAE 650 M, showing a wider potential use of this chromatographic support for their purification at a preparative level.

High resolution of multiple forms of red blood cell enzymes using a Toyopearl DEAE 650 S

We have investigated a new anion exchange chromatographic support (Toyopearl DEAE 650 S) which simultaneously allows easily to remove hemoglobin from hemolysates and to obtain a very high resolution of enzymes present in multiple forms. The results obtained are better than those obtainable using an anion-exchange HPLC column. The data obtained at analytical level suggest a wider use of this new matrix also for preparative purposes without significant changes in the resolution.

Role of hexokinase in the regulation of glucose metabolism in human erythrocytes

Red blood cell glucose metabolism was studied in erythrocytes from a patient with trisomy 10 p which resulted in + 50% hexokinase specific activity, in normal controls and in cases of heterozygous hexokinase deficiency. The results obtained show that the hexokinase activity level is an important factor in the control of the erythrocyte's glycolytic rate while having no appreciable effect on the hexose monophosphate pathway under resting conditions. No clear conclusion could be drawn when an oxidative stress was present.

Rabbit red blood cell hexokinase. Decay mechanism during reticulocyte maturation

In rabbit reticulocytes, the hexokinase (EC 2.7.1.1)-specific activity is 4-5 times that of corresponding mature red cells. Immunoprecipitation of hexokinase by a polyclonal antibody made in vitro shows that this maturation-dependent hexokinase decay is not due to accumulation of inactive enzyme molecules but to degradation of hexokinase. A cell-free system derived from rabbit reticulocytes, but not mature erythrocytes, was found to catalyze the decay of hexokinae activity and the degradation of 125I-labeled enzyme. This degradation is ATP-dependent and requires both ubiquitin and a proteolytic fraction retained by DEAE-cellulose. Maximum ATP-dependent degradation was obtained at pH 7.5 in the presence of MgATP. MgGTP could replace MgATP with a relative stimulation of 0.90. 125I-Hexokinase incubated with reticulocyte extract in the presence of ATP forms high molecular weight aggregates that reach a steady-state concentration in 1 h, whereas the degradation of the enzyme is linear up to 8 h, suggesting that the formation of protein aggregates precedes enzyme catabolism. These aggregates are stable upon boiling in 2% sodium dodecyl sulfate, 3% mercaptoethanol and probably represent an intermediate step in the enzyme degradation with hexokinase and other proteins covalently conjugate to ubiquitin. That hexokinase could be conjugated to ubiquitin was shown by the formation of 125I-ubiquitin-hexokinase complexes in the presence of ATP and the enzymes of the ubiquitin-protein ligase system. Thus, the decay of hexokinase during reticulocyte maturation is ATP- and ubiquitin-dependent and suggests a new physiological role for the energy-dependent degradation system of reticulocytes.

Human erythrocyte hexokinases are immunologically related

Human erythrocytes contain three major hexokinase isoenzymes eluted by DE-52 chromatography between hexokinase type I and type II. Cross-reactivities of these isoenzymes were studied by means of a monospecific rabbit antibody against purified human placenta hexokinase type I. It was shown that the three hexokinase isoenzymes were immunologically related, supporting the concept of a postsynthetic mechanism(s) as their origin.

Rat red blood cell hexokinase purification, properties and age-dependence

Rat erythrocytes, in contrast to red blood cells from other mammals, have been shown to contain only one hexokinase isozymic form identified as type I by chromatographic and kinetic properties. Rat reticulocytes contain 3.6-times the hexokinase activity found in mature erythrocytes but exactly the same isozyme. By a combination of ion-exchange chromatography, dye-ligand chromatography and high-pressure liquid chromatography the rat erythrocyte hexokinase was purified more than 84 000-fold to a specific activity of 143 units/mg protein and shown to be homogeneous by sodium dodecyl sulfate-gel electrophoresis. The native protein showed a molecular weight of 100 000 by gel-filtration and an apparent molecular weight of 98 000 under denaturating conditions in sodium dodecyl sulfate-gel electrophoresis. The isoelectric point was shown to be 6.3 pH units. This data provides evidence of only one form of hexokinase in the erythrocytes of a mammal.

Glucose metabolism in fibroblasts from patients with erythrocyte hexokinase deficiency

Four different hexokinase (HK) isoenzymes are distributed in different proportions in human tissues. Fibroblasts contain HK type I as the predominant glucose phosphorylating activity, the same isoenzyme that predominates in red blood cells (RBC). We have established cell lines from two patients homozygous for RBC HK deficiency but carrying different mutations. In one case (HK-Melzo) the residual RBC enzyme shows a marked heat instability but possesses normal kinetic and regulatory properties; in the other (HK-Napoli), the enzyme is characterized by an increased Ki for glucose-1,6-diphosphate. These properties are also retained by the fibroblasts' hexokinase. Glucose utilization by cultured fibroblasts from these patients was markedly reduced in the cell lines where HK deficiency was more pronounced. However, cells with only 30% HK activity retained their full ability to utilize glucose in the hexose monophosphate pathway. This was shown to be true not only under basal conditions but also in the presence of oxidative agents such as methylene blue. Significant reduction of the ATP level was also found in HK-Melzo fibroblasts. Thus, HK deficiency is associated with reduced glucose utilization and normal hexose monophosphate shunt rates. Results previously obtained on RBC support similar conclusions.

Human erythrocyte hexokinase deficiency: a new variant with abnormal kinetic properties

A 14-month-old child who had a haemolytic episode when he was 5 years old, and with psychomotor retardation, was found to have decreased red cell hexokinase activity. The mutant enzyme was characterized by an increased affinity for glucose associated with an increased inhibition constant for glucose-1,6-diphosphate. Affinity for Mg ATP2-, heat stability and pH-optimum were normal. The isozymic pattern of the red cell enzyme was normal but all the molecular forms were present in reduced amounts. The kinetics of decay of hexokinase during cell ageing was also normal. Glucose consumption of the hexokinase deficient cells was 60-65% of the controls while the amount metabolized through the hexose monophosphate shunt was unchanged. Red cell 2,3-diphosphoglycerate and glucose-6-phosphate levels were normal in the proband but reduced in the erythrocytes of his parents, who were heterozygous for the defect but had normal haematological data. Comparison with the 13 previously reported cases of hexokinase deficiency confirms the broad phenotypic variability that characterizes this disorder.

Regulatory properties of human erythrocyte hexokinase during cell ageing

Human red blood cell hexokinase exists in multiple molecular forms with different isoelectric points but similar kinetic and regulatory properties. All three major isoenzymes (HK Ia, Ib, and Ic) are inhibited competitively with respect to Mg.ATP by glucose 6-phosphate (Ki = 15 microM), glucose 1,6-diphosphate (Ki - 22 microM), 2,3-diphosphoglycerate (Ki = 4 mM), ATP (Ki = 1.5 mM), and reduced glutathione (Ki = 3 mM). All these compounds are present in the human erythrocyte at concentrations able to modify the hexokinase reaction velocity. However, the oxygenation state of hemoglobin significantly modifies their free concentrations and the formation of the Mg complexes. The calculated rate of glucose phosphorylation, in the presence of the mentioned compounds, is practically identical to the measured rate of glucose utilization by intact erythrocytes (1.43 +/- 0.15 mumol h-1 ml red blood cells-1). Hexokinase in young red blood cells is fivefold higher when compared with the old ones, but the concentration of many inhibitors of the enzyme is also cell age-dependent. Glucose 6-phosphate, glucose 1,6-diphosphate, 2,3-diphosphoglycerate, ATP, and Mg all decay during cell ageing but at different rates. The free concentrations and the hemoglobin and Mg complexes of both ATP and 2,3-diphosphoglycerate with hemoglobin in the oxy and deoxy forms have been calculated. This information was utilized in the calculation of glucose phosphorylation rate during cell ageing. The results obtained agree with the measured glycolytic rates and suggest that the decay of hexokinase during cell ageing could play a critical role in the process of cell senescence and destruction.

Relationship between the rate of erythrocyte hexose monophosphate pathway and the glucose 6-phosphate concentration

Erythrocytes of individuals with increased (+ 50%) or reduced (-35%) hexokinase activity contain respectively 70 and 17 nmole/ml RBC of glucose-6-phosphate (normal concentration 30 +/- 5nmole/ml RBC) and show comparable rates of the HMP (60 +/- 5nmole/hr/ml RBC). Similarly, in RBC of different ages, obtained by density gradient ultracentrifugation, the glucose-6-phosphate concentration range from 57 (young cells) to 18 (old cells) nmole/ml RBC but the rate at which glucose is utilized in the HMP is unchanged. These data exclude a regulatory role of glucose 6-phosphate in the HMP even if its concentration is under that required for maximal G6PD activity.

Hexokinase in developing rabbit erythroid cells

The activity and isozyme distribution of hexokinase were studied in bone marrow cells from normal and anemic rabbits separated by density centrifugation or by unit-gravity sedimentation. The specific activity of the enzyme was found to be about 150-fold higher in the basophilic erythroblasts as compared with the mature circulating erythrocytes. Most of the falls in hexokinase activity take place when the cell completes its final division and matures from the polychromatic stage to the orthochromatic stage. Concomitant with this strong decrease in enzyme activity, qualitative as well as quantitative changes in the hexokinase isozymic pattern become apparent. While in the basophilic and polychromatic erythroblasts the only hexokinase isozyme present is hexokinase type I, the orthochromatic cells also contain hexokinase Ib. This last isozymic form, which increases further at the reticulocyte stage, is also present in the circulating reticulocytes but not in mature red blood cells.

Purification and properties of the cytoplasmic hexokinase from rabbit brain

About 90% of the total hexokinase activity in rabbit brain was found to be associated with mitochondria while the remaining part was found in the cytosolic fraction. The soluble enzyme was purified 4,700-fold to near homogeneity by a combination of ion-exchange chromatography, dye-ligand chromatography and affinity chromatography. The purified enzyme showed a specific activity of 110 units/mg of protein and was obtained in 70% yield. The molecular weight of the purified hexokinase was found to be approximately 98,000 both for the native and the denatured enzyme. The isoelectric point, pI, was 6.2 pH units by isoelectric focusing and the enzyme was found to be able to phosphorylate several hexoses. Mg . ATP2-, among the nucleotide substrates, was the most effective phosphate donor. The properties of the purified cytoplasmatic hexokinase were compared with those of the solubilized mitochondrial enzyme. No significant differences were found in molecular weight, isoelectric point, pH dependence of activity, electrophoretic mobility and affinity for glucose and Mg.ATP2-. However, the temperature dependence of activity, and the specificity for several hexose substrates were markedly different.

Rabbit red blood cell hexokinase:intracellular distribution during reticulocytes maturation

The intracellular localization and isozyme distribution of hexokinase were studied during rabbit reticulocyte maturation and aging. In reticulocytes 50% of the enzyme was particulate while in the mature erythrocytes all the hexokinase activity was soluble. The bound enzyme co-sediments with mitochondria and by column chromatography it was found to be hexokinase Ia. The cytosol of reticulocytes contains hexokinase Ia (38%) and hexokinase Ib (62%) while the mature erythrocytes contain only hexokinase Ia. The amount of bound hexokinase decreases very quickly during cell maturation and aging as was shown by following in vivo reticulocyte maturation or by analysis of hexokinase compartmentation in cells of different ages, obtained by density gradient ultracentrifugations. A role for this intracellular distribution of hexokinase is suggested.

Regulatory properties of rabbit red blood cell hexokinase at conditions close to physiological

The true level of hexokinase in rabbit erythrocytes was determined by three different methods, including the spectrophotometric glucose-6-phosphate dehydrogenase coupled assay and a new radioisotopic assay. The value found at 37 degrees C (pH 7.2) was 10.23 +/- 1.90 mumol/h per ml red blood cells, which is lower than previously reported values. More than 40 cellular components of the rabbit erythrocytes were tested for their effects on the enzyme. Their intracellular concentrations were also determined. Several of these compounds were found to be competitive inhibitors of the enzyme with respect to Mg X ATP2-. Furthermore, reduced glutathione at a concentration of 1 mM was able to maintain hexokinase in the reduced state with full catalytic activity. The ability of orthophosphate to remove the inhibition of some phosphorylated compounds was examined under conditions similar to cellular (pH 7.2 and 50 microM of orthophosphate) and found to be of no practical interest. In contrast, the binding of ATP4- and 2,3-diphosphoglycerate to the rabbit hemoglobin significantly modifies their intracellular concentrations and the formation of the respective Mg complexes. The pH-dependence of the reaction velocity and of the kinetic properties of the enzyme in different buffer systems were also considered. This information was computerized, and the rate of glucose phosphorylation in the presence of the mentioned compounds was determined. The value obtained, 1.94 +/- 0.02 mumol/h per ml red blood cells, is practically identical to the measured rate of glucose utilization by intact rabbit erythrocytes (1.92 +/- 0.3 mumol/h per ml red blood cells). These results provide further evidence for the central role of hexokinase in the regulation of red blood cell glycolysis.

Rabbit red blood cell hexokinase. Evidences for an ATP-dependent decay during cell maturation

Rabbit hexokinase (EC 2.7.1.1) has been shown to exist in reticulocytes as two distinct molecular forms, designated hexokinase Ia and Ib, but only one of these was consistently present in mature red cells. In vivo, hexokinase Ia and Ib show a decay rate of 3 and 8% a day, respectively, while in vitro they show a similar stability. The possibility that the proteolytic activities of the reticulocyte could be responsible for the fast decay of hexokinase was investigated. No differences were found in the decay rates of hexokinase Ia and Ib during in vitro reticulocyte maturation in presence or absence of proteolytic inhibitors. Contrariwise, many findings indicate the ATP-dependent proteolytic system of the reticulocyte as a possible mechanism. In fact, the decay of hexokinase and the degradation of 3H-globins are both stimulated by ATP and ubiquitin; they show similar kinetic properties and both disappear during reticulocyte maturation. The cellular localization of hexokinase Ia and Ib was shown to be responsible for the differences found between their decay rates.

Pig red blood cell hexokinase: evidence for the presence of hexokinase types II and III, and their purification and characterization

Pig erythrocytes, in contrast to red blood cells from other mammals (M. Magnani, V. Stocchi, F. Canestrari, M. Dachà, and G. Fornaini (1982) Biochem. Int. 4, 673), have been shown to contain hexokinase (EC 2.7.1.1) types II and III. Hexokinase type III is the predominant form, accounts for 98% of the total glucose phosphorylating activity, and has been purified 290,000-fold by a combination of ion-exchange chromatography and affinity chromatography on Sepharose-N-hexanoylglucosamine. The enzyme was shown to be homogeneous by polyacrylamide and sodium dodecyl sulfate-gel electrophoresis. The highest specific activity obtained was 190 units/mg protein with a yield of 60%. Because the amount of hexokinase II was small, it was only partially purified by ion-exchange chromatography. The native proteins have the same molecular weight of 100,000 by gel filtration on Ultrogel AcA44. The apparent isoelectric point of hexokinase type II was shown to be 4.8 and 4.9 pH units, whereas hexokinase type III was shown to have a pI of 4.3 to 4.4 pH units by isoelectric focusing. Both hexokinases are able to phosphorylate several hexoses. However, while hexokinase II shows an apparent Km for glucose of 1.5 X 10(-4) M with negative cooperativity (nH = 0.4), hexokinase III shows an apparent Km for glucose of 1.5 X 10(-5) M and a positive cooperative effect (nH = 1.5). Furthermore, glucose at concentrations higher than 0.4 mM becomes an inhibitor of hexokinase III. Amino acid analysis of hexokinase type III revealed a low number of the aromatic residues Phe, Tyr, and Trp; this is in agreement with the low extinction coefficient of E1%280nm = 12.5.

Pig red blood cell hexokinase: regulatory characteristics and possible physiological role

The regulatory properties of pig erythrocyte hexokinase III have been studied. Among mammalian erythrocyte hexokinases, the pig enzyme shows the highest affinity for glucose and a positive cooperative effect with nH = 1.5 at all the MgATP concentrations studied (for 0.5 to 5 mM). Glucose at high concentrations is also an inhibitor of hexokinase III. Similarly, the apparent affinity constant for MgATP is independent of glucose concentration. Uncomplexed ATP and Mg are both competitive inhibitors with respect to MgATP. Glucose 6-phosphate, known as a stronger inhibitor of all mammalian erythrocyte hexokinases, is a poor inhibitor for the pig enzyme (Ki = 120 microM). Furthermore, this inhibition is not relieved by orthophosphate as with other mammalian red blood cell hexokinases. A variety of red blood cell-phosphorylated compounds were tested and found to be inhibitors of pig hexokinase III. Of these, glucose 1,6-diphosphate and 2,3-diphosphoglycerate displayed inhibition constants in the range of their intracellular concentrations. In an attempt to investigate the role of hexokinase type III in pig erythrocytes some metabolic properties of this cell have been studied. The adult pig erythrocyte is able to utilize 0.27 mumol of glucose/h/ml red blood cells (RBC) compared with values of 0.56-2.85 mumol/h/ml RBC for the other mammalian species. This reduced capacity to metabolize glucose results from a relatively poor ability of the cell membrane to transport glucose. In fact, all the glycolytic enzymes were present and a low intracellular glucose concentration was measured (0.5 mM against a plasma level of 5 mM). Furthermore, transport and utilization were concentration-dependent processes. Inosine, proposed as the major energy substrate of the pig erythrocyte, at physiological concentrations is not as efficient as glucose in maintaining reduced glutathione levels under oxidative stress. Furthermore, newborn pig erythrocytes (fully permeable to glucose) possess hexokinase type II as the predominant glucose-phosphorylating activity. This fact and the information derived from the study of the regulatory characteristics of hexokinase III and from metabolic studies on intact pig erythrocytes permit the hypothesis that the presence of this peculiar hexokinase isozyme (type III) enables the adult pig erythrocyte to metabolize low but appreciable amounts of glucose.

The age-dependent metabolic decline of the red blood cell

The oxidative and non-oxidative utilization of glucose was evaluated in human erythrocytes of different ages, separated by density gradient ultracentrifugation. Young red blood cells are able to metabolize 2.5 times more glucose than old ones; on the other hand, the amount of glucose utilized via the hexose monophosphate shunt does not show any age dependence. Glucose metabolism evaluated during in vivo ageing of a rabbit red cell population shows results very similar to those obtained for human cells. Metabolic stimulation of glucose utilization by high phosphate in both young and old human red cells increases glucose utilization by 40%. In the same way young and old erythrocytes were able to increase the amount of glucose metabolized via the hexose monophosphate shunt when an oxidative stimulus (methylene blue) was introduced. Human erythrocytes of different age possess similar abilities to transport glucose so that an age-dependent defect in glucose transport can be excluded. The ATP content of human and rabbit red blood cells, as a function of cell age, follows the decrease in glucose metabolized via the Embden-Meyerhof pathway. Reduced glutathione, on the other hand, after a small decrease associated with the "maturation" of reticulocytes into red cells, remains constant like the rate of the hexose monophosphate shunt.

Red blood cell glucose metabolism in trisomy 10p: possible role of hexokinase in the erythrocyte

Red blood cell glucose metabolism was investigated in a male patient with de novo trisomy 10p. According to previous evidence, when assigning hexokinase gene locus in the 10p11 leads to pter region, a triplex dosage effect of hexokinase activity (HK) was found, while all the other erythrocyte glycolytic enzymes were in the normal values range. Red blood cell glucose utilization was 2.87 mumole/hr/ml RBC as compared to 1.43 in normal controls; the rate of glucose metabolized through the hexose monophosphate shunt (HMPS) was unchanged. Glucose-6-phosphate, fructose-6-phosphate, fructose-1,6-diphosphate, and dihydroxyacetone phosphate increased with respect to normal controls, while normal levels of 3-phosphoglycerate, 2-phosphoglycerate, phosphoenolpyruvate, and ATP were found. The HK activity increased in all the red blood cell fractions obtained by density gradient ultracentrifugation. However, a small difference in the distribution of cells through the gradient was evident. The experiments reported in this article show that in the red blood cells of patients with trisomy 10p, an increased level of HK leads to higher concentrations of glucose-6-phosphate and to a faster glucose utilization in the Embden-Meyerhof pathway, while the HMPS rate is unchanged.

Red blood cell galactokinase activity and presenile cataracts

Red blood cell galactokinase activity was measured in 70 patients with cataracts to assess a possible correlation between galactokinase activity levels and risk of cataract development. Among all, 15 patients developed cataracts during the first year of life, 25 patients under the age of 50 and 30 later in life. No cases of total or partial galactokinase deficiency were found. These results, taken together with the absence of cataracts in 9 patients with partial galactokinase deficiency render less certain the cause and effect relationship between partial galactokinase deficiency and the appearance of cataracts.

Molecular forms of red blood cell hexokinase

Mammalian red blood cell hexokinase has been shown to exist in two or more distinct molecular forms, which are separable by ion-exchange chromatography. Of these forms just one corresponds to hexokinase type I from other tissues, while the others differ from any previously reported hexokinase isozyme. Analysis of several molecular properties of the three major forms (Ia, Ib and Ic in the order of their elution from DE-52 columns) of hexokinase prepared from human red cells and of the two forms purified from rabbit reticulocytes, shows significant differences in the isoelectric point. The kinetic and regulatory characteristics, the molecular weight, the temperature and pH-dependence of the various isozymes were similar. The hexokinase isozymic pattern is largely dependent upon red blood cell age. Among all, hexokinase Ib is the predominant form in rabbit reticulocytes and becomes the minor component in the older cells; a similar situation has also been found in the human erythrocyte. At present the molecular basis of hexokinase heterogeneity remains unknown, however preliminary experimental findings indicate a post-translational modification as a possible mechanism.

Multiple forms of human red blood cell hexokinase. Preparation, characterization, and age dependence

Human red blood cell hexokinase (EC 2.7.1.1) has been shown to exist in multiple molecular forms which are separable by ion exchange chromatography. Of the major forms, designated hexokinase Ia, Ib, and Ic, only hexokinase Ia corresponds to hexokinase type I from human liver, while the others differ from every other previously reported hexokinase isozyme. Hexokinase Ib is the predominant form in the fetal erythrocytes, while it is present at lower levels in the red blood cells of adults. Analysis of the hexokinase isozymic pattern in red cells of different mean age shows that the level of hexokinase Ib is also dependent on the age of the cell. The three major forms of hexokinase have the same molecular weight of 100,000, by sedimentation velocity on sucrose density gradients, the same Michaelis constants, substrate and coenzyme specificity, pH-dependent activity, and the same thermal stability. The only significant differences were found in the isoelectric points which were 5.7 pH units for hexokinase Ia, 5.5 pH units for hexokinase Ib, and 5.35 pH units for hexokinase Ic. These data, together with that previously reported for rabbit erythrocytes (Stocchi, V., Magnani, M., Canestrari, F., Dachà, M., and Fornaini, G. (1981) J. Biol. Chem. 256, 7856-7861) suggest that the presence of multiple forms of hexokinase is a common phenomenon in mammalian red blood cells.

A new variant of galactokinase

A new variant of human galactokinase activity is described. This enzyme shows reduced catalytic activity both in red and white blood cells, lower Km for ATPMg2-, and increased in vivo instability when compared to the normal enzyme. Thermostability and pH optimum are not modified. We have labelled this enzyme the Urbino variant and have suggested the procedure to distinguish it from the allelic form (GALKG) responsible for galactosemia in the homozygous state.