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Biomedical subjects

M Magnani

Publications and source records attributed to M Magnani.

At least 235 records · Page 13Linked to original sources
PubMed1984

Human plasma glutathione oxidation in normal and pathological conditions.

Reduced glutathione added to human plasma disappears rapidly, and it is concomitantly recovered in its oxidized form. This oxidation is not due to the plasma metal content since it is not inhibited by EDTA or by passage of plasma through Chelex columns. Furthermore, this oxidation is not due to the peroxidase activity of glutathione S-transferases, which are usually undetectable in normal human serum, and it does not correlate with the amount of plasma glutathione peroxidase. A significant increase in the rate of glutathione oxidation was observed in plasma of patients with increased gamma-glutamyltranspeptidase activity. It is concluded that the side-oxidase activity of gamma-glutamyltransferase is responsible for the oxidation of glutathione in human plasma.

Glutathione↗
PubMed1983

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.

Amino Acids↗
PubMed1983

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.

Adenosine Triphosphate↗
PubMed1983

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.

Animals↗
PubMed1983

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.

Adenocarcinoma↗
PubMed1983

Prenatal prediction of duplication 10q24 leads to qter by gene dosage of GOT1 on uncultured amniotic cells.

Glutamic-oxaloacetic transaminase (GOT1) gene dosage studies were performed on uncultured amniotic cells from a fetus at risk for duplication/deficiency of 10q24 leads to qter, due to maternal translocation t(9;10)(p24;q24). Previous investigations in the same pedigree had shown triplex dosage effect of GOT1 on red blood cells of a 10q24 leads to qter trisomic fetus monitored by midtrimester amniocentesis. In the present pregnancy, the GOT1 activity of amniotic cells exhibited a triplex gene dosage, suggesting duplication of region 10q24 leads to qter in the fetus. The biochemical prediction was confirmed two weeks later by cytogenetic analysis.

Adult↗
PubMed1983

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.

Adolescent↗
PubMed1983

Rabbit red blood cell hexokinase. Mechanism of decay during cell life-span.

Rabbit red blood cells contain hexokinase type I whereas in the reticulocyte two distinct molecular forms (HK Ia and Ib) are present. One (HK Ia) corresponds to hexokinase type I from other tissues, while the other differs from any previously reported isozyme. Rabbit bone marrow cells contain hexokinase type I and II. However, when the erythroid precursor cells become predominant over the non-erythroid cells (during phenylhydrazine anemia) a great increase of HK Ia can be observed concomitant with the appearance of HK Ib. Fractionation of the bone marrow cells on density gradients provides evidence that basophil erythroblasts and proerythroblasts contain only HK Ia while HK Ib appears at the reticulocyte stage. Maturation and ageing of circulating reticulocytes are associated with the decrease of hexokinase activity. Since the decay rate of HK Ib is about three times higher than the decay rate of HK Ia, the mature erythrocytes do not contain appreciable amounts of HK Ib. Furthermore, in vitro, HK Ia and Ib possess similar stabilities so that a cellular mechanism must be responsible of their in vivo different decay rates. This mechanism, as reported in this paper, is ATP-dependent, could be found in the soluble fraction, and is active only at the reticulocyte stage. These properties are similar to those of the ATP-dependent proteolytic system. Pure ubiquitin, an essential polypeptide of the ATP-dependent proteolytic system, is also able to catalyze the decay of hexokinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

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.

Blood Glucose↗
PubMed1983

[The problematical painful knee. An arthroscopic study of 300 cases].

The diagnosis of internal derangements of the knee sometimes presents a graft deal of difficulty. If today the expression "Internal derangement of the knee" is much more rare, it is due to the progress made in the field of diagnosis thanks, in particular, to arthrography and arthroscopy. The authors report the results of 300 arthroscopies of the knee. They present the most significant forms of the problem knee: hypertrophy of the adipose tissue, hypertrophy of the synovial folds, villo-nodular synovitis, synovial chondromatosis, radiolucent mobile foreign bodies, osteochondritis dessicans hidden meniscal lesions and specific and non-specific mono-arthritis. In the majority of cases, the clinical suspicion was confirmed, but in 29% of cases arthroscopy corrected the diagnosis. Arthroscopy, is judged to be of great value in the diagnosis of doubtful forms of the painful knee syndrome. Often it eliminates the need to open the joint and almost always directs the incision to the most appropriate region and, above all, it prevents the risk of unnecessary operation.

Adolescent↗
PubMed1982

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.

Aging↗
PubMed1982

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.

Adult↗
PubMed1982

Adult and fetal galactokinases in human red blood cells.

This paper reports the biochemical properties of galactokinase from fetal and adult human red blood cells. The specific activity of galactokinase is three times higher in the fetal red cells than in adult cells, shows a significant difference in the Michaelis constant toward galactose, and is more thermostable. On the other hand, no differences were found in molecular weight, electric charge, temperature and pH dependence between the two enzymes partly purified from fetal and adult erythrocytes. The possibility that these differences could be due to the shorter lifespan of the fetal erythrocytes (which could result in a higher proportion of young cells in the blood samples utilized) was investigated. Fetal and adult red blood cells were separated into fractions of different mean age by ultracentrifugation through density gradients. The kinetic properties and thermostability of galactokinase from fetal erythrocytes do not show any similarity with the same properties of the enzyme from young red blood cells. These results indicate that galactokinase from fetal erythrocytes show some biochemical properties that are typical signs distinguishing a fetal enzyme.

Adult↗