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Biomedical subjects

M Magnani

Publications and source records attributed to M Magnani.

At least 217 records · Page 12Linked to original sources
PubMed1985

Hexokinase in human chorionic villi.

The level, intracellular distribution, and isozymic pattern of hexokinase (EC 2.7.1.1) were determined on human chorionic villi obtained by trophoblast biopsy in the first trimester of pregnancy. About 50% of total hexokinase activity was found to be particle-bound and 96% of this in the overt form (i.e. assayable without the addition of detergents). Both soluble and particulate hexokinase show the same affinities for glucose but differ in the affinity for MgATP2- and in their sensitivity to glucose 1,6-diphosphate inhibition. By chromatographic and kinetic methods the soluble hexokinase was found to be represented by isozymes I, II and traces of hexokinase III while most of the bound enzyme was hexokinase type I. These results provide evidence for the expression of at least three hexokinase isozymes in early human development and can partially explain the high rate of glucose utilization of the placenta.

Adenosine Triphosphate↗
PubMed1985

Autologous fitted incus versus Plastipore PORP in ossicular chain reconstruction.

Hearing results and causes of failure with three types of ossicular reconstruction techniques over an intact stapes, during second-stage intact canal wall tympanoplasty, are reported herein. The three types of reconstruction are: fitted autologous incus (38 cases); Plastipore PORP with cartilage (41 cases); Plastipore PORP without cartilage (32 cases). A residual air-bone gap within 15 dB. was found in 63.2 per cent of fitted includes, in 41.5 per cent of PORPs with cartilage, and in only 37 per cent of PORPs without cartilage. Eighty-four per cent fitted incudes, 63 per cent PORPs with cartilage and 44 per cent PORPs without cartilage yielded a residual air-bone gap within 25 dB. Extrusion has been the main cause of failure among Plastipore prostheses.

Biocompatible Materials↗
PubMed1985

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.

Blood Glucose↗
PubMed1985

Hereditary nonspherocytic hemolytic anemia due to a new hexokinase variant with reduced stability.

A 27-year-old woman with severe chronic hemolytic anemia was found to have reduced red cell hexokinase activity when the degree of reticulocytosis was considered. This enzyme had normal pH-dependent activity, normal Km for glucose, fructose, and mannose, normal Km for Mg adenosine triphosphate (ATP)2- and Ki for glucose-1,6-diphosphate. Furthermore, the pH-dependence and orthophosphate dependence of Ki for glucose-1,6-diphosphate were normal. However, this hexokinase was inactivated rapidly at 44 degrees C. No abnormalities were found in the red cell hexokinase isozymic pattern when it was compared with the profile obtained from cells of similar age. The hexokinase specific activity was reduced in all the red blood cell fractions obtained by density gradient ultracentrifugation; a marked difference in the distribution of cells through the gradient was evident. Among the glycolytic intermediates, a significant decrease of 2,3-diphosphoglycerate was evident. ATP and glucose 6-phosphate were also reduced when compared with cells of similar. Glucose consumption of the hexokinase-deficient cells decreased, but the rate of glucose metabolized through the hexose monophosphate shunt was unchanged. Although the total hexokinase activity in lymphocytes was only reduced by 37%, a marked hexokinase deficiency was detected in blood platelets (20% to 25% of normal activity). The parents and one of two siblings of the patient were heterozygous for the defect, with 66% to 74% of normal erythrocyte hexokinase activity and reduced heat stability of the enzyme. These results, when compared with those obtained in previously reported cases of hexokinase deficiency, provide further evidence of the broad phenotypic variability that characterizes this disorder. Furthermore, it is suggested that failure of energy generation is probably the primary cause of hemolytic anemia in hexokinase deficiency.

Adult↗
PubMed1984

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.

Chromosomes, Human, 6-12 and X↗
PubMed1984

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.

Anemia↗
PubMed1984

[Hexokinase in bone marrow cells in the rabbit].

The hexokinase isozymic pattern of circulating reticulocytes fractionated by density gradient ultracentrifugation was studied. All the cellular fractions obtained show similar ratio of hexokinase Ia/hexokinase Ib while a four fold decay in specific activity was evidenced. Bone-marrow cells of anemic rabbits also contain low amounts of HK Ib while this isozymic form is not present in basophilic erythroblasts.

Anemia↗
PubMed1984

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.

2,3-Diphosphoglycerate↗
PubMed1984

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.

Animals↗
PubMed1984

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.

Adenosine Triphosphate↗
PubMed1984

Effect of cholecystokinin octapeptide and ceruletide on release of acetylcholine from cerebral cortex of the rat in vivo.

The effect of cholecystokinin octapeptide (CCK-8) and its analogue, ceruletide on release of acetylcholine (ACh) from the cerebral cortex was investigated in urethane-anaesthetized and in unanaesthetized rats. Cholecystokinin octapeptide and ceruletide markedly stimulated output of ACh at doses of 1.5 and 5.0 micrograms/kg (i.p.), respectively. This effect was prevented by proglumide (160 mg/kg i.p.), a specific cholecystokinin receptor antagonist. At doses of 10 micrograms/kg (i.p.) and more, both CCK-8 and ceruletide decreased output of ACh from the cerebral cortex. The decrease was prevented by naloxone (1 mg/kg, s.c.), and replaced by a short-lasting increase. Cholecystokinin octapeptide and ceruletide appear therefore to affect the activity of cortical cholinergic fibres by acting upon both specific and opiate receptors. The interaction between CCK-8 and ceruletide, and opiate receptors either direct or through the release of endogenous opiates, was also demonstrated by the antagonism between ceruletide (1, 5 and 10 micrograms/kg, i.p.) and analgesia induced by morphine (5 mg/kg, s.c.), evaluated by the tail-flick test in the rat.

Acetylcholine↗
PubMed1984

Regional mapping of hexokinase-1 within the short arm of chromosome 10.

Hexokinase-1 (HK1) activity was determined in red cells of 5 patients with partial duplications of chromosome 10, all of which involved the 10p region. In 4 patients the levels of HK1 activity were higher than the mean activity of controls, strongly indicating a triplex dosage effect. The most likely regional assignment for HK1 would appear to be 10p11.2.

Child↗
PubMed1984

Red blood cell hexokinase in Fanconi's anemia.

The activity of ten red blood cell enzymes, including hexokinase, has been measured in 6 Fanconi's anemia patients. In disagreement with previous reports, in no instance were reduced or increased hexokinase levels found. Furthermore, the hexokinase isozymic pattern, thermostability, pH dependence of activity and kinetic properties were also in the normal range.

Adolescent↗
PubMed1984

Failures with Plasti-Pore ossicular replacement prostheses.

Plasti-Pore ossicular prosthesis failures found in our series of 246 patients with regular follow-up are reported and analyzed. Extrusions as well as poor functional results (postoperative air-bone gap greater than 25 dB) of the prostheses with and without cartilage on top have been reviewed. The overall extrusion rate was 9.3%: a higher extrusion rate occurred with prostheses without cartilage (18.4%) than with cartilage (4.4%). Thirty-six patients among those with poor postoperative hearing improvement have undergone revision surgery: the main causes of failure were a short prosthesis, a fixed stapes or footplate, adhesions of the prosthesis to surrounding structures, and the displacement of the prosthesis.

Cochlear Implants↗