Search PubMed⌕ Search

Biomedical subjects

P Vanni

Publications and source records attributed to P Vanni.

At least 55 records · Page 3Linked to original sources
PubMed1985

[Anionic detergents, natural and synthetic, as selective denaturants of various dehydrogenases].

The effects of natural (fatty acids) or synthetic detergents on some highly purified enzymes has been studied. Four dehydrogenases (glucose-6-phosphate-, lactico-, malico- and isocitrico-dehydrogenase) are highly inhibited by these products. Other enzymes are not inhibited or inactivated by them. The mechanism of the action of detergents is specifically based on their binding to the enzyme at the level of its proteic constituent and close to its active group.

Animals↗
PubMed1985

Detergents as selective inhibitors and inactivators of enzymes.

In order to study the detergent-enzyme interaction and to clarify whether such an interaction produces specific or non-specific effects, we investigated the action of natural and synthetic detergents on enzymatic systems of different levels of complexity (crystalline enzymes, crude homogenates, organ preparations, organisms in toto i.e. rats and germinating seeds). The enzyme-detergent interaction was examined both as a time-independent phenomenon (inhibition) and as a time-dependent phenomenon (inactivation). In in vitro experiments a clear inhibition of pyridine-dependent dehydrogenases by long-chain anionic detergents was found. Cationic detergents have their greatest effect on lipase, LDH, MDH and ICDH from rat liver homogenates. At low concentrations SDS inactivates all the dehydrogenase enzymes studied. With high concentrations (10 mM) of SDS and dodecyltrimethylammonium bromide (C12), there was a sharp and non-specific decrease of enzymatic activities. In the in vivo studies, rats were given detergents to drink; the cationic detergent (C12) was far more effective than SDS with enzymes from both intestine and liver homogenates. SDS and C12 do not seem to interfere with enzyme activities at the beginning of the germination of Pinus pinea and Triticum durum seeds. However a marked reduction of activities does occur at the respective maximum germination times of these seeds. The nonionic detergent is ineffective both as inhibitor and as inactivator.

Alcohol Dehydrogenase↗
PubMed1984

On the interaction between synthetic detergents and enzymatic proteins.

Eight highly purified and crystalline enzymes representative of fundamental metabolic pathways and of cellular structure were tested with seven detergents. The enzyme-detergent interaction was studied as a time-independent (inhibition) or time-dependent (inactivation) phenomenon. Our results imply a specificity of detergent action on the enzymes studied.

Alanine Transaminase↗
PubMed1984

[Interaction : detergents-enzymes].

The study on the action of eight synthetic detergents of various types of well defined structure and properties (neutral, anionic, cationic) has been realized on fourteen highly purified enzymes of animal or vegetal origin of great metabolic importance, on these of homogenates of intestine or liver of normal rats and of rats fed during a relatively long period with food containing synthetic detergents. The action of all studied detergents on highly purified enzymes has been characterized as this of specific effectors, producing a reversible denaturation of enzymatic proteins to whom they combine. Ingestion of detergents by rats leads, probably by the same mechanism, to a diminution in vivo of the activity of some intestinal and hepatic enzymes.

Animals↗
PubMed1983

Isocitrate lyase: artifacts and multiple enzyme forms.

Multiple enzyme forms of isocitrate lyase from various sources have been frequently reported. Protease action after cell rupture was sporadically claimed to explain the observed multiple enzyme forms. In this communication studies which are consistent with a protease action in vitro on isocitrate lyase of Pinus pinea germinating seeds are reported. Moreover, changes in DEAE-Sephacel patterns, mainly related to the age of germination, were observed. Differences regarding the heat stability of the detected enzyme forms were also found. The results indicate that isocitrate lyase from P. pinea may be detected in at least three different forms, one of which is heat stable and may be obtained only at the early stages of germination.

Chromatography, DEAE-Cellulose↗
PubMed1983

The palmitoleate: a natural selective denaturant of enzymes.

A study has been carried out in order to explain the enzyme-palmitoleate interaction. The highly purified and crystalline enzymes representative of fundamental metabolic pathways were: alcohol dehydrogenase (ADH), lactate dehydrogenase (LDH), malate dehydrogenase (MDH), isocitrate dehydrogenase (ICDH), glucose-6-phosphate dehydrogenase (G6P-DH), alkaline phosphatase. The enzyme-palmitoleate interaction was studied as a phenomenon time-independent (inhibition) and time-dependent (inactivation). Palmitoleate inhibited remarkably LDH, MDH, ICDH and G6P-DH. A kinetic analysis of the inhibitory action of palmitoleate on LDH and MDH was also carried out. Inactivation studies have shown that ADH and alkaline phosphatase are not sensitive to palmitoleate action, unlike the other enzymes. A comparison was made between the action of palmitoleate and that of a synthetic anionic detergent, sodium dodecyl sulfate (SDS).

Alcohol Dehydrogenase↗
PubMed1983

[Phosphoric esters of vitamin D2 and D3, new substrates for alkaline phosphatase of the bovine intestine].

Phosphate esters of vitamins D2 and D3 (D2-O-P and D3-O-P) are hydrolyzed by the alkaline phosphatase from calf intestine (CAPase). pH optimum and Km values are in agreement with those reported for other substrates for intestinal alkaline phosphatase. No effect of activation was noted at low concentrations of D2-O-P and D3-O-P (10(-5)-10(-4)M) in contrast with that stated in earlier works. At higher concentrations (1-4 mM) of the phosphorilated vitamins, accordingly with their function as substrates of CAPase, an inhibitory effect on the hydrolysis of p-nitrophenylphosphate was observed.

Alkaline Phosphatase↗
PubMed1982

Susceptibility to proteinases of yeast enzymes selectively modified by fatty acids.

To investigate a possible correlation between selective modification and degradation of enzymes, the susceptibility to intracellular yeast proteinases A and B of yeast enzymes treated with fatty acids was tested. Enzymes used were glucose-6-phosphate dehydrogenase (EC 1.1.1.49) and 3-phosphoglycerate kinase (EC 2.7.2.3), which are sensitive to the denaturing modification caused by fatty acids, and alcohol dehydrogenase (EC 1.1.1.1) which is insensitive. Proteinases and substrate enzymes were all pure preparations. Without modification by fatty acids, at neutral pH, the three enzymes are remarkably resistant to degradation by both proteinases. Treatment with myristic or oleic acid definitely enhances the susceptibility to proteolysis of the sensitive glucose-6-phosphate dehydrogenase and 3-phosphoglycerate kinase, whereas it leaves negligible that of the insensitive alcohol dehydrogenase. The selective effect of fatty acids on the degradation is pH-dependent: with proteinase A it was lost at acidic pH. Since intracellular levels of free fatty acids near or even higher than 1 mM were actually measured in yeast cells, it is possible that free fatty acids, in some cellular conditions, affect yeast enzyme composition. However, the control of specific enzyme degradation in yeast is still an open question.

Alcohol Dehydrogenase↗
PubMed1982

Specific interaction among some enzymes and sodium dodecyl sulfate.

The effect of 1-butanesulfonic acid sodium salt and sodium dodecyl sulfate on the activity of highly purified and crystalline enzymes with marked differences in structure and function has been studied. The enzymes were: alcohol dehydrogenase; lactate dehydrogenase; malate dehydrogenase; isocitrate dehydrogenase; glucose-6-phosphate dehydrogenase; lipase; alkaline phosphatase. While 1-butanesulfonic acid sodium salt, at the studied concentrations, resulted generally inactive, sodium dedecyl sulfate showed a selective inhibitory effect, always under the critical micellar concentration. A kinetic analysis of the inhibitory action was also carried out.

Alkaline Phosphatase↗
PubMed1982

Isocitrate lyase of conifers (Pinus pinea).

1. Isocitrate lyase has been purified about 60 times from the conifer Pinus pinea. A first characterization was made. 2. The high instability is an important feature of this enzyme from higher plants, this causes serious problems in the purification and characterization. 3. A substantial agreement with the data from the literature was found for what concerns pH dependence of Vmax and pKm, the effect of bivalent cations and the requirement of Mg2+. 4. Kinetic studies gave evidence for a mechanism ordered uni-bi with glyoxylate being the last product released, kinetic constants were calculated, no evidence for cooperative effects was found. 5. Equilibrium constant by Haldane method calculation agrees with value calculated with isocitrate lyase from the bacterium Pseudomonas indigofera.

Cations, Divalent↗
PubMed1982

[Sodium dodecyl sulfate, concurrent inhibitor of several dehydrogenases].

The effect of sodium dodecyl sulfate on the activity of highly purified or crystalline enzymes has been studied. The enzymes were: lactate dehydrogenase (LDH), malate dehydrogenase (MDH). isocitrate dehydrogenase (ICDH), glucose-6-phosphate dehydrogenase (G6P-DH), lipase, alkaline phosphatase. Sodium dodecyl sulfate, always under the critical micellar concentration, shows a selective inhibitory effect. A kinetic analysis of the inhibitory action on LDH, MDH, ICDH and G6P-DH was also carried out.

Alkaline Phosphatase↗
PubMed1981

An example of enzyme hysteresis. The slow and tight interaction of some fully competitive inhibitors with small intestinal sucrase.

Of the fully competitive inhibitors of small intestinal sucrase investigated in this or in other papers, acarbose, nojirimycin, and deoxynojirimycin (Fig. 2) have the highest affinity for the enzyme, their Ki values being in the 10(-7)-10(-8) M range. Furthermore, thier interaction with the enzyme is slow, the steady state being reached in their presence in a matter of minutes. Their overall "on" and "off" constants are small, which indicates that a conformational change accompanies the interaction of these substances with the active site of intestinal sucrase. The structure of these inhibitors, as well as the pH dependence of their Ki values, agrees with and allows additions to be made to the catalytic mechanism earlier suggested for this enzyme (Cogoli, A., and Semenza, G. (1975) J. Biol. Chem. 250, 7802-7809). None of these inhibitors of sucrase has any sizeable effect on the small intestinal Na+-dependent D-glucose transport system.

1-Deoxynojirimycin↗
PubMed1980

Continuous optical assay of sucrase and other glucosidases.

A continuous optical method for the assay of glucose-releasing hydrolases is reported. Particular emphasis is given to the assay of purified sucrase from rabbit small intestine. The procedure requires glucose dehydrogenase and mutarotase. In the presence of the latter enzyme, the initial lag is substantially shortened when glucose is released as alpha-anomer. Under the test conditions used, the method shows a good proportionality up to an activity of 0.2 units/3 ml and may also be applied for measuring the activity in crude homogenates.

Animals↗
PubMed1979

Na+-dependent, electroneutral L-ascorbate transport across brush border membrane vesicles from guinea pig small intestine.

In brush border vesicles from guinea pig small intestine L-ascorbate transport is Na+-dependent and electroneutral (in the presence of Na+, as shown by its lack of response to either positive or negative delta psi across the membrane). L-Ascorbate transporter has the kinetic characteristics of a mobile carrier (Km for L-ascorbate, 0.3 mM). D-Isoascorbate (erythorbate) seems to be another, but poorer, substrate of the same transporter. L-Ascorbate transport is subjected to heterologous inhibition by D-glucose.

Animals↗
PubMed1979

Studies on isocitrate lyase isolated from Lupinus cotyledons.

Isocitrate lyase (threo-DS-isocitrate glyoxylate-lyase, EC 4.1.3.1) was isolated from cotyledons of Lupinus seedlings, purified 100-fold with respect to its initial specific activity and characterized (Km, pH optimum, Mg2+ requirement, sulfhydryl inhibitors, and synthase activity). The final purified preparation consisted of two homogeneous protein bands clearly separated by electrophoresis on polyacrylamide gel and chromatography on Sephadex G 200. Reducing agents are necessary for the maintenance of enzyme activity. The most effective reducing agent studied was 1,4-dithioerythreitol. The effect of several metabolites (oxalate, malonate, phosphoenolpyruvate, succinate, malate, tartrate, gluconate-6-phosphate, sorbose, sorbitol, and inositol) on the activity of purified preparations was tested. Oxalate proved to be the strongest inhibitor, seconded closely by phosphoenolpyruvate. The spectral characteristics of the purified enzyme are as follows: ultraviolet peak at 280 nm and fluorescence peak at 340 nm. The solid state infrared spectrum of the enzyme (lyophilized) showed that the enzyme was mostly in the alpha-helix conformation with very slight random orientation.

Chloromercuribenzoates↗
PubMed1978

Selective denaturation of several yeast enzymes by free fatty acids.

The denaturation of eight purified yeast enzymes, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase, alcohol dehydrogenase, beta-fructosidase, hexokinase and glucose-6-phosphate isomerase, promoted under controlled conditions by the free fatty acids myristic and oleic, is selective. Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADP+ 1 oxidoreductase, EC 1.1.1.49) is extremely sensitive to destabilization and was studied in greater detail. Results show that chain length and degree of unsaturation of fatty acids are important to their destabilizing effect, and that ligands of the enzyme can afford protection. The denaturation process results in more than one altered form. These results can be viewed in the perspective of the possibility that amphipathic substances, and in particular free fatty acids, may play a role for enzyme degradation in vivo, by initiating steps of selective denaturation.

Alcohol Oxidoreductases↗
PubMed1977

Stimulation of isocitrate lyase biosynthesis by hydroxylamine and hydrazine.

Recently it has been demonstrated that hydroxylamine is an activator of triglyceride catabolism. We have studied the effect of hydroxylamine on isocitrate lyase activity and lipid catabolism and have noted a stimulation of isocitrate lyase biosynthesis by 5 mM hydroxylamine. The specificity of this effect was tested with a number of representative enzymes of other metabolic pathways. In an attempt to study the possible mechanism of action of hydroxylamine we have also tested the effects of two substances that are structural or functional analogues of hydroxylamine, namely, ethanolamine and hydrazine, both on the enzyme level in plant cultures and on the activity of enzyme preparations. From our data we may conclude that "de nove" biosynthesis of isocitrate lyase depends on the reaction of hydroxylamine or hydrazine with glyoxylate to give the corresponding oxime and hydrazone. The removal of glyoxylate from the biological equilibrium in this way could cause extra formation of isocitrate lyase.

Dose-Response Relationship, Drug↗