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Biomedical subjects

E Meucci

Publications and source records attributed to E Meucci.

35 records · Page 2Linked to original sources
PubMed1985

Ascorbic acid stability in aqueous solutions.

Different water purity provokes a great variation of the stability of ascorbic acid and isoascorbic acid solutions. The effect of temperature on ascorbate aerobic oxidation was assessed by means of Arrhenius plots from which thermodynamic parameters were derived. The presence of bovine serum albumin drastically reduces the vitamin oxidation rate regardless of stereoisomerism. On the other hand the interaction with alkaline phosphatase, an enzyme inhibited by preincubation with vitamin C, does not modify significantly the stability in the experimental conditions used.

Alkaline Phosphatase↗
PubMed1984

Characterization of alkaline phosphatase inactivation by ascorbic acid.

Ascorbic acid, isoascorbic acid and dehydroascorbic acid inhibit bovine kidney alkaline phosphatase activity. Ascorbic acid free radicals seem not to be involved. Dialysis does not make the inactivation reversible. A competitive mechanism can be inferred from experiments with phosphate and substrates, which block the activity decay. The influence of temperature, pH, other inhibitors and tertiary structure modifications on the inactivation process is also investigated.

Alkaline Phosphatase↗
PubMed1984

Studies on the selective chemical inhibition by urea of alkaline phosphatase isoenzymes in the reaction course.

Urea inhibits the activity of alkaline phosphatase during the reaction course. The inactivation is progressively stronger for the placental, intestinal and renal subforms. Influence of reaction temperature, pH, type and molarity of buffer, magnesium chloride, albumin and enzyme concentration on the inactivation mechanism is evaluated. In all experimental conditions the process follows pseudofirst-order kinetics and the inactivation profiles are distinct and typical for each enzymatic subform. With a simple graphical analysis, a single inactivation curve in controlled experimental conditions, allows the identification of each isoenzyme from the slope and the calculation of the respective fractional amount from the intercept of the time-activity plot.

Alkaline Phosphatase↗
PubMed1983

Effect of general anesthetics on human granulocyte chemiluminescence.

The effect of general anesthetics on human granulocyte 'phagocytic capacity' was tested, both in vivo and in vitro, by means of chemiluminescence. Halothane and ethrane produced a consistent degree of chemiluminescence inhibition, which, in vitro, was clearly dose-dependent.

Anesthesia, General↗
PubMed1983

Ascorbic acid and alkaline phosphatase activity.

Ascorbic acid is found strikingly to decrease the activity of bovine kidney alkaline phosphatase in vitro. The inhibition of alkaline phosphatase is a function of ascorbic acid concentration and is time and temperature dependent. The presence of the substrate protects the enzyme against the inhibitory action of the vitamin.

Alkaline Phosphatase↗
PubMed1983

In vitro effect of ascorbic acid on bovine kidney alkaline phosphatase activity.

A striking decrease of bovine kidney alkaline phosphatase activity is observed in vitro when the catalytic assay is performed after preincubation of the enzyme with ascorbic acid (AA). The inhibitory effect is a function of AA concentration time and on temperature. Activity decay follows an exponential biphasic course as a function of preincubation time composed by a "fast" phase in the first half hour and by a later "slow" phase of inhibition. Both the rise in preincubation temperature and the increase of the amount of vitamin enhance the degree of inhibition. Ascorbic acid is ineffective as inhibitor when added together with the substrate, p-nitrophenyl phosphate, which in fact markedly stabilizes the enzyme even when present in unsaturating amounts.

4-Nitrophenylphosphatase↗
PubMed1983

Modulation of alkaline phosphatase in different organs by ascorbic acid and related compounds.

The organ-specific modulation by ascorbic acid and related compounds on alkaline phosphatase activity of calf intestinal and human placental tissues has been studied at pH 8.0 and 37 degrees C. L(+)-ascorbic acid and its isomer D(-)-ascorbic acid inhibit to a similar extent the intestinal isoenzyme and appear to be more potent modifiers than dehydro-L-(+)-ascorbic acid. In contrast, the placental isoenzyme shows an initial activation by the three chemical agents, followed by an inhibition. The inhibition is lower with L(+)-ascorbic acid and D(-)-ascorbic acid, while its catalytic activity is affected only slightly by dehydro-L-(+)ascorbic acid.

Alkaline Phosphatase↗
PubMed1982

Vitamin C in normal human mononuclear and polymorphonuclear leukocytes.

Human peripheral leukocytes from healthy donors have been isolated by means of a suitable separation method to obtain a high yield of lymphocytes and granulocytes with a very low contamination of platelets and red blood cells. Mononuclear cells so purified contain more than double amounts of vitamin C than polymorphonuclear cells. The difference between lymphocytes and granulocytes content also tends to be larger at increasing vitamin concentrations in total leukocytes. A higher level of vitamin C is displayed by the mononuclear cells obtained from women in respect to men, while no significant difference is found in the polymorphonuclear cells.

Adolescent↗
PubMed1981

[Colorimetric determination of plasma vitamin C: comparison between 2,4-dinitrophenylhydrazine and phosphotungstic acid methods (author's transl)].

The evaluation of a recently published colorimetric method for plasma ascorbic acid determination, using phosphotungstic acid (PTA), was performed by comparison with the largely employed 2,4-dinitrophenylhydrazine (DNPH) procedure. The method has been evaluated according to International Federation of Clinical Chemistry (I.F.C.C.) recommendations. In particular, calibration procedures have been performed and precision, accuracy, linearity, specificity and sensitivity have been studied in biological samples. Linear regression analysis indicates that the two methods do not correlate completely. The PTA method shows a better recovery. The PTA method shares with the DNPH procedure a poor precision at low concentrations of vitamin C in plasma such as to make results less reliable at the clinically significative levels.

Ascorbic Acid↗
PubMedDate not supplied

Vitamin C-bovine serum albumin binding behaviour.

The binding of ascorbic acid and dehydroascorbic acid to bovine serum albumin is greatly heterogeneous. The Hill plots, as evaluated from the fluorescence quenching measurements, clearly show a biphasic behaviour. Scatchard analysis moreover indicates that the potency and the pattern of the binding can change gradually in the process of occupation of various sites because of albumin structural modifications.

Ascorbic Acid↗
PubMedDate not supplied

Modifications induced by ascorbic acid on alkaline phosphatase fluorescence.

Ascorbic acid, isoascorbic acid and dehydroascorbic acid quench the tryptophyl fluorescence of alkaline phosphatase. The quenching is protein aspecific, although its extent reflects the different inhibitory efficiency of the compounds. The kinetic inactivation and emission deactivation of alkaline phosphatase isoenzymes present also striking similarities. The fluorescence modifications, moreover, show a particular pattern, indicative of a transition phenomenon. The quenching effects displayed by the ascorbic system on alkaline phosphatase can then supply an interesting insight into other aspects of the inhibitor-enzyme interaction.

Alkaline Phosphatase↗
PubMedDate not supplied

A kinetic approach to the evaluation of alkaline phosphatase inactivation by urea.

A kinetic approach is described which enables the measurement of the enzyme inactivation rate constant during the reaction course. A mathematical analysis is presented and it is shown that a time-dependent step may be postulated to exist. Reaction kinetics follow an exponential rule with time as the independent variable and enzymatic activity as the dependent variable. A simple procedure of graphical analysis is reported and the influence on the inactivation rate constant of various conditions (temperature and inhibitor concentration) is evaluated. The method is illustrated by an experimental model: the inactivation of bovine kidney alkaline phosphatase by urea.

Alkaline Phosphatase↗
PubMedDate not supplied

Interaction between alkaline phosphatase and ascorbic acid by fluorescence and absorption studies.

Very low amounts of ascorbic acid modify alkaline phosphatase fluorescence, absorption and enzymatic activity. A strong quenching of enzyme, tryptophan and tyrosine emission together with evident alterations of the protein absorption characteristics are observed. The catalytic activity inhibition probably reflects a perturbation of the active site environment due to the interaction of ascorbic acid with enzyme aminoacyl residues.

Alkaline Phosphatase↗