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G Liguri

Publications and source records attributed to G Liguri.

At least 37 records · Page 2Linked to original sources
PubMed1993

Acylphosphatase induced modifications in the functional properties of erythrocyte membrane sodium pump.

Human red cell acylphosphatase actively hydrolyzes the Na+/K(+)-ATPase phosphoenzyme from erythrocyte membrane. This effect occurred with amounts of acylphosphatase (up to 10 units/mg membrane protein) within the physiological range, and the low value of the apparent Km (0.147 +/- 0.050 microM) indicates that the enzyme has a high affinity for this substrate. When added at the above concentration to inside out vesicles from human erythrocytes, acylphosphatase significantly enhanced the rate of strophantidine-sensitive ATP hydrolysis. The same amounts of acylphosphatase stimulated, although to a lower extent, the rate of ATP-dependent 22Na+ influx (normal efflux). Thus, the calculated stoichiometry for Na+/ATP was 2.68 in the absence of acylphosphatase and 1.06 in the presence of 10 units/mg vesicle protein of the enzyme. Conversely, acylphosphatase addition strongly decreased the rate of ATP-dependent 86Rb+(K+) efflux (normal influx) which, with 10 units/mg vesicle protein, was almost suppressed. As a consequence, the Na+/Rb+ ratio, calculated as 1.52 in the absence of acylphosphatase rose to 72.5 in the presence of 10 units/mg vesicle protein of this enzyme. These results suggest that, because of its hydrolytic activity on the phosphoenzyme intermediate, acylphosphatase 'uncouples' erythrocyte membrane Na+,K+ pump. Possible mechanisms for this effect are discussed.

Acid Anhydride Hydrolases↗
PubMed1993

Cerebral soluble ubiquitin is increased in patients with Alzheimer's disease.

A study concerning the amount of soluble ubiquitin in different cortical and subcortical regions of brains from patients with Alzheimer's disease compared to the amount in normal brains is presented. Several samples from 9 brain regions were processed and analyzed by liquid chromatography. In almost all the investigated cerebral regions the soluble ubiquitin content was significantly higher in pathologic tissue than in normal tissue. The primary structure of ubiquitin isolated from brain tissue affected by Alzheimer's degenerative processes was determined and resulted to be identical to normal human ubiquitin. These findings, together with the detection of polyubiquitinated proteins in paired helical filaments of neurofibrillary tangles described by several authors, suggest that an impairment of the process of intracellular, ubiquitin-dependent proteolysis might play an important role in the pathogenesis of this neurodegenerative disease. On the other hand, the expression of the correct polypeptide sequence in brain with Alzheimer's disease seems to exclude a mutation of the polyubiquitin gene as a cause of these alterations.

Adult↗
PubMed1992

Alterations induced by acylphosphatase in the activity of heart sarcolemma calcium pump.

We studied the effect of muscle acylphosphatase on the Ca2+ pumping ATPase of heart sarcolemma. Acylphosphatase addition to calmodulin-depleted sarcolemmal vesicles produced a significant increase in the rate of Ca(2+)-dependent ATP hydrolysis, even higher than obtained with exogenously added calmodulin. Maximal stimulation (about four fold over basal value) was obtained with 550 units/mg vesicle protein, a concentration that fall within the physiological range. Conversely, similar amounts of acylphosphatase decreased the rate of ATP-dependent Ca2+ transport into the sarcolemmal vesicles. The maximal statistically significant inhibition of Ca2+ uptake was observed with the same acylphosphatase concentration that gave the maximal stimulation of Ca(2+)-ATPase activity. From these findings acylphosphatase appears to reduce the efficiency of heart sarcolemmal Ca2+ pump with an impairment of the coupling between ATP hydrolysis and Ca2+ transport. A possible mechanism of this effect is discussed.

Acid Anhydride Hydrolases↗
PubMed1991

Effects of acylphosphatase on the activity of erythrocyte membrane Ca2+ pump.

Acylphosphatase, purified from human erythrocytes, actively hydrolyzes the acylphosphorylated intermediate of human red blood cell membrane Ca(2+)-ATPase. This effect occurred with acylphosphatase amounts (up to 10 units/mg membrane protein) that fall within the physiological range. Furthermore, a very low Km value, 3.41 +/- 1.16 (S.E.) nM, suggests a high affinity in acylphosphatase for the phosphoenzyme intermediate, which is consistent with the small number of Ca(2+)-ATPase units in human erythrocyte membrane. Acylphosphatase addition to red cell membranes resulted in a significant increase in the rate of ATP hydrolysis. Maximal stimulation (about 2-fold over basal) was obtained at 2 units/mg membrane protein, with a concomitant decrease in apparent Km values for both Ca2+ and ATP. Conversely, similar amounts of acylphosphatase significantly decreased (by about 30%) the rate of Ca2+ transport into inside-out red cell membrane vesicles, albeit that reduced apparent Km values for Ca2+ and ATP were also observed in this case. A stoichiometry of 2.04 Ca2+/ATP hydrolyzed was calculated in the absence of acylphosphatase; in the presence of acylphosphatase optimal concentration, this ratio was reduced to 0.9. Acylphosphatase activity, rather than just protein, was essential for all the above effects. Taken together these findings suggest that, because of its hydrolytic activity on the phosphoenzyme intermediate, acylphosphatase reduces the efficiency of the erythrocyte membrane Ca2+ pump. A possible mechanism for this effect is that the phosphoenzyme is hydrolyzed before its transport work can be accomplished.

Acid Anhydride Hydrolases↗
PubMed1991

Hydrolysis by acylphosphatase of erythrocyte membrane Na+, K(+)-ATPase phosphorylated intermediate.

Acylphosphatase, purified from human erythrocytes, actively hydrolyzes the phosphoenzyme intermediate of human red blood cell membrane Na+, K(+)-ATPase. This effect occurred with acylphosphatase amounts (up to 10 units/mg membrane protein) that fall within the physiological range. Acylphosphatase addition to erythrocyte membranes resulted in a significant increase in the rate of Na+, K(+)-dependent ATP hydrolysis. Maximal stimulation, observed with 10 units/mg membrane protein, was of about 80% over basal value. The same acylphosphatase amount enhanced of about 40% the rate of ATP driven Na+ transport into inside out red cell membrane vesicles. Taken together these findings suggest a potential role of acylphosphatase in the control of the activity of erythrocyte membrane Na,K pump.

Acid Anhydride Hydrolases↗
PubMed1990

Changes in Na+,K(+)-ATPase, Ca2(+)-ATPase and some soluble enzymes related to energy metabolism in brains of patients with Alzheimer's disease.

Hexokinase, lactate dehydrogenase, acylphosphatase, (Na+,K+)-ATPase and Ca2(+)-ATPase of selected areas from postmortem Alzheimer's disease brains were studied. Hexokinase and lactate dehydrogenase were significantly changed in all the examined subcortical nuclei. (Na+,K+)-ATPase activity was altered in several areas of Alzheimer's disease brains. No changes in Ca2(+)-ATPase and acylphosphatase were observed. The main alterations of the assayed enzymes were observed in subcortical areas but not in cortical areas of Alzheimer's disease brains.

Aged↗
PubMed1990

Effect of acylphosphatase on human erythrocyte membrane Ca2(+)-ATPase.

We studied the effect of human acylphosphatase on the activity of human erythrocyte membrane Ca2(+)-ATPase. Both the acylphosphatase that is contained in hemolysate and the purified enzyme isolated from red blood cells were able to stimulate Ca2(+)-ATPase activity in erythrocyte membranes. Given the same acylphosphatase activity, however, the hemolysate showed higher stimulatory effect than the purified enzyme. Acylphosphatase stimulation was additive to that induced by calmodulin, thus indicating that acylphosphatase acts in a calmodulin-independent manner. Trifluoperazine, a calmodulin antagonist, did not inhibit acylphosphatase-induced stimulation of Ca2(+)-ATPase activity. Acylphosphatase significantly decreased the rate of Ca2+ influx into inside-out erythrocyte membrane vescicles, thus acting as Ca2+ pump inhibitor. Taken together these findings indicate that acylphosphatase is a soluble, non-calmodulin activator of erythrocyte membrane Ca2(+)-ATPase and might be involved in the control of calcium transport across the plasma membrane.

Acid Anhydride Hydrolases↗
PubMed1990

Isolation and quantitation of ubiquitin from rat brain.

A fast and sensitive method for the isolation and quantitation of cytoplasmic ubiquitin from brain by reversed-phase high-performance liquid chromatography is described. Cytosol from brain tissue was obtained by differential centrifugation and, after perchloric acid treatment, the sample was concentrated and ubiquitin was quantitatively isolated by means of a single chromatographic run. The amino acid composition, molecular weight, and primary structure of the pure protein were identified. The addition of monoiodinated 125I-ubiquitin to the sample as an internal standard indicated high native ubiquitin recovery. Statistical analysis carried out on different preparations and standardization of the chromatographic system indicated both the accuracy and the reproducibility of the method.

Amino Acid Sequence↗
PubMed1990

Increased acylphosphatase levels in erythrocytes, muscle and liver of tri-iodothyronine treated rabbits.

To explore a possible role of acylphosphatase in the regulation of energy metabolism, we measured this enzyme's activity and content in skeletal muscle, liver and erythrocytes of normal and tri-iodothyronine treated rabbits. Besides acylphosphatase we assayed (Na+ + K+)-ATPase, Ca2(+)-ATPase and several enzymes of carbohydrate metabolism. Acylphosphatase activity in erythrocytes rose steadily during treatment with triiodothyronine (25 micrograms/Kg per day for 5 weeks), and its increase occurred earlier and was much more pronounced than that of other soluble enzymes. In erythrocytes of treated animals (Na+ + K+)-ATPase declined whereas Ca2(+)-ATPase activity increased, in agreement with previously reported findings. In muscle and liver of the treated animals acylphosphatase activity was about twice as high as in the controls; in these tissues we found also increased activities for (Na+ + K+)-ATPase, fructose-1,6-bisphosphatase and glucose-6-phosphatase. In any case, among the enzymes we examined, acylphosphatase was one of the most strongly and regularly stimulated by the treatment. Furthermore we observed, through an immunochemical procedure, that there was a congruence between increases in acylphosphatase activity and content. On the basis of these results we conclude that the rise in acylphosphatase levels in treated animals is probably due to its increased biosynthesis. The possible significance of these findings in the metabolic modifications associated with hyperthyroidism are discussed.

Acid Anhydride Hydrolases↗
PubMed1990

Immunoaffinity purification and immunoassay determination of human erythrocyte acylphosphatase.

Specific anti-human erythrocyte acylphosphatase antibodies were raised in rabbits, purified by affinity chromatography, and used to develop an enzyme purification procedure based on an immunoaffinity chromatography step. This procedure permitted the rapid purification of the enzyme, with a high final yield and with a specific activity very similar to that found for the enzyme purified by the standard procedure. The noncompetitive enzyme-linked immunoadsorbent assay developed with the affinity-purified antibodies was very specific and sensitive in that a positive reaction could be detected in the presence of antigen amounts of as little as 0.01 ng/ml. By this assay the enzyme content was determined in normal cells, tissues, and organs as well as in blood samples from hemopathy-affected patients. This test could possibly have clinical applications.

Acid Anhydride Hydrolases↗
PubMed1989

Increased acylphosphatase levels in erythrocytes from hyperthyroid patients.

Acylphosphatase activity and content were measured in erythrocytes from hyperthyroid patients and healthy controls. In addition, the soluble enzymes glucose-6-phosphate dehydrogenase, hexokinase, and the membrane bound (Na+ + K+)-ATPase and Ca2+-ATPase were assayed. Our results confirmed previous studies indicating a decrease of (Na+ + K+)-ATPase and an increase of Ca2+-ATPase activity in hyperthyroid erythrocytes. While glucose-6-phosphate dehydrogenase was not significantly changed, hexokinase and acylphosphatase activities were significantly higher in the hyperthyroid group. Both activities and content of acylphosphatase returned to normal levels in erythrocytes from treated patients, when they were euthyroid. These findings suggest that an excess of thyroid hormones may stimulate acylphosphatase biosynthesis in erythroid cells and indicate a potential clinical usefulness of this enzyme in hyperthyroidism.

Acid Anhydride Hydrolases↗
PubMed1989

Regional assignment of the loci for adenylate kinase to 9q32 and for alpha 1-acid glycoprotein to 9q31-q32. A locus for Goltz syndrome in region 9q32-qter?

Normal levels of adenylate kinase (AK-1) and of alpha 1-acid glycoprotein (ORM1) were found in a girl with a deletion 9q32-qter secondary to a maternal translocation (4q35; 9q32), thus excluding these loci from the deleted region. These results, and comparison with other informative data, map the locus for AK-1 to 9q32 and that for ORM1 to region 9q31-q32. The girl has several signs of the Goltz syndrome (Focal dermal hypoplasia), which is listed in the McKusick catalog (no. 30560) as an X-linked dominant condition. Our finding indicates that the locus for Golz syndrome is autosomal and in region 9q32-qter or that there are two such conditions, one autosomal and one X-linked.

Adenylate Kinase↗
PubMed1988

Post-mortem modifications of the specific activity of some brain enzymes.

The post-mortem stability of some brain enzymes was studied. Over the time period under examination, the cytoplasmic enzymes investigated underwent a decisive decay, hexokinase being the most labile and acylphosphatase the most stable. On the other hand, structured activities such as Na+, K+-ATPase and Ca2+, Mg2+-ATPase showed an apparent transitory increase. The differences in post-mortem stability of soluble enzymes could be ascribed, at least in part, to their different susceptibility toward proteolytic activities, as suggested by the electrophoretic results.

Animals↗
PubMed1988

Acylphosphatase increases the rate of ethanol production from glucose in cell-free extracts of Saccharomyces cerevisiae.

Addition of acylphosphatase exerted a stimulating effect on the alcoholic fermentation of glucose by Saccharomyces cerevisiae. The rates of glucose degradation and ethanol production by cell-free extracts of the S-288C strain were measured in the absence and in the presence of various levels of this enzyme. Two acylphosphatase isoenzymes were used; one was purified from horse skeletal muscle and the other from human erythrocytes. Both increased the rate of alcoholic fermentation, but that from erythrocytes proved to be the more efficient. This stimulating action is probably due to an "uncoupling effect" of acylphosphatase on the fermentative process, through hydrolysis of 3-phosphoglyceroyl phosphate. This was demonstrated by the fact that alcoholic fermentation was stimulated considerably by a mixture of ADP and inorganic phosphate and by arsenate as well. The possibility of improving the fermentative capacity of microorganisms may have important biotechnological applications.

Acid Anhydride Hydrolases↗
PubMed1987

Acylphosphatase levels of human erythrocytes during cell ageing.

Human erythrocytes contain an acylphosphatase isoenzyme, whose concentration during cell ageing was determined by an enzyme immunoassay. Erythrocytes were age-fractionated by isopycnic centrifugation in "Percoll" density gradients. Acylphosphatase concentration was found to rise with the increase of cell density. Maximum values were attained in the mature erythrocytes and there was only a slight decrease in the older cells. Acylphosphatase activity in human erythrocytes of different ages followed a similar pattern, a finding which was confirmed for rabbit red cells with different levels of reticulocytes. The most probable mechanism for the increase of acylphosphatase content and activity during red cell maturation appears to be a de novo synthesis of this enzyme during the reticulocyte stage and its storage, virtually unaffected, in the mature erythrocytes. The possible consequences of increased acylphosphatase levels on the metabolic modifications associated with erythrocyte ageing are discussed.

Acid Anhydride Hydrolases↗
PubMed1986

A new acylphosphatase isoenzyme from human erythrocytes: purification, characterization, and primary structure.

A new acylphosphatase from human erythrocytes was isolated by an original purification procedure. It is an isoenzyme of the well-characterized human skeletal muscle acylphosphatase. The erythrocyte enzyme shows hydrolytic activity on acyl phosphates with higher affinity than the muscle enzyme for some substrates and phosphorylated inhibitors. The sequence was determined by characterizing the peptides purified from tryptic, peptic, and Staphylococcus aureus V8 protease digests of the protein, and it was found to differ in 44% of the total positions as compared to the human muscle enzyme. About one-third of these differences are in the form of strictly conservative replacements. The protein consists of 98 amino acid residues; it has an acetylated NH2-terminus and does not contain cysteine: (sequence in text).

Acid Anhydride Hydrolases↗
PubMed1986

Sarcoplasmic reticulum Ca2+-ATPase and acylphosphatase activities in muscle biopsies from patients with Duchenne muscular dystrophy.

Sarcoplasmic reticulum Ca2+-ATPase, acylphosphatase and other soluble enzymes (creatine kinase, lactate dehydrogenase, aldolase and pyruvate kinase) were assayed in muscle biopsies from patients affected by Duchenne muscular dystrophy (DMD) and from normal controls. Specific activities of all the soluble enzymes were decreased in dystrophic muscle, acylphosphatase exhibiting the most marked and significant decrease comparable to that of creatine kinase, in spite of a moderate increase in serum levels. Also, Ca2+-ATPase, particularly the calcium-dependent activity, was decreased in dystrophic muscle. A positive correlation, higher than with the other soluble enzymes, was obtained between acylphosphatase specific activity and the percentage of Ca2+-activation of Ca2+-ATPase. These findings: suggest an impairment of microsomal calcium uptake which could be, at least in part, responsible for sarcoplasmic calcium accumulation observed in DMD; do not disagree with an hypothesized role of acylphosphatase in intracellular calcium homeostasis, consistent with the enzyme's demonstrated hydrolytic activity on the phosphorylated intermediate of Ca2+-ATPase.

Acid Anhydride Hydrolases↗