scholarly journals Modification of myo-inositol monophosphatase by the arginine-specific reagent phenylglyoxal

1989 ◽  
Vol 264 (2) ◽  
pp. 419-422 ◽  
Author(s):  
R G Jackson ◽  
N S Gee ◽  
C I Ragan
Keyword(s):  
Protective Effect ◽  
Competitive Inhibitor ◽  
Small Degree ◽  
Arginine Residue ◽  
Inositol Monophosphatase ◽  
Degree Of Protection ◽  
Uncompetitive Inhibitor ◽  
Enzyme Intermediate ◽  
Specific Reagent

myo-Inositol monophosphatase is inhibited by the arginine-specific reagent phenylglyoxal. The rate of inactivation is decreased in the presence of Pi, a competitive inhibitor of the enzyme. The effect of Pi is dependent on the presence of Mg2+, but is unaffected by Li+, an uncompetitive inhibitor. In the absence of Mg2+, the substrate, Ins(1)P, binds to the enzyme but is not converted into products, and affords only a small degree of protection against inactivation by phenylglyoxal. Li+ had no further effect under these conditions, but in the presence of Mg2+ caused a marked potentiation of the protective effect of substrate alone. In the absence of substrate, Li+ had no effect on activation by phenylglyoxal. Incorporation of 14C-labelled phenylglyoxal showed that inactivation was associated with modification of a single arginine residue per monomer in the dimeric enzyme. These findings support a mechanism in which Li+ inhibits monophosphatase by trapping a phosphorylated enzyme intermediate and preventing its hydrolysis.

scholarly journals Evidence for the importance of arginine residues in pig kidney alkaline phosphatase

1979 ◽  
Vol 181 (1) ◽  
pp. 137-142 ◽  
Author(s):  
M N Woodroofe ◽  
P J Butterworth
Keyword(s):  
Alkaline Phosphatase ◽  
Active Site ◽  
Competitive Inhibitor ◽  
Arginine Residue ◽  
Pig Kidney ◽  
Close Proximity ◽  
Arginine Residues ◽  
Km Value ◽  
Uncompetitive Inhibitor ◽  
Kidney Alkaline Phosphatase

The arginine-specific reagents 2,3-butanedione and phenylglyoxal inactivate pig kidney alkaline phosphatase. As inactivation proceeds there is a progressive fall in Vmax. of the enzyme, but no demonstrable change in the Km value for substrate. Pi, a competitive inhibitor, and AMP, a substrate of the enzyme, protect alkaline phosphatase against the arginine-specific reagents. These effects are explicable by the assumption that the enzyme contains an essential arginine residue at the active site. Protection is also afforded by the uncompetitive inhibitor NADH through a partially competive action against the reagents. Enzyme that has been exposed to the reagents has a decreased sensitivity to NADH inhibition. It is suggested that an arginine residue is important for NADH binding also, although this residue is distinct from that at the catalytic site. The protection given by NADH against loss of activity is indicative of the close proximity of the active and NADH sites.

scholarly journals Interaction of difluoro-oxaloacetate with aspartate transaminase

1977 ◽  
Vol 161 (2) ◽  
pp. 383-387 ◽  
Author(s):  
P A Briley ◽  
R Eisenthal ◽  
R Harrison ◽  
G D Smith
Keyword(s):  
Steady State ◽  
Competitive Inhibitor ◽  
Aspartate Transaminase ◽  
Steady State Kinetic ◽  
High Concentrations ◽  
State Kinetic ◽  
Uncompetitive Inhibitor

Diffluoro-oxaloacetate behaves as a competitive inhibitor of 2-oxoglutarate and as an uncompetitive inhibitor with respect to aspartate in steady-state kinetic experiments with cytoplasmic aspartate transaminase. In the presence of high concentrations of aspartate transaminase, difluoro-oxaloacetate is slowly transaminated to difluoro-aspartate, suggesting its use as a kinetic probe to study the reactions of the aminic form of the enzyme.

Receptor kinetics pertaining to blockade of nerve-released transmitter at synapses

1988 ◽  
Vol 233 (1273) ◽  
pp. 461-475 ◽  
Keyword(s):  
Channel Blocker ◽  
Competitive Inhibitor ◽  
Tissue Response ◽  
Receptor Density ◽  
Receptor Kinetics ◽  
Tissue Responses ◽  
Competitive Inhibitors ◽  
Transmitter Substance ◽  
Uncompetitive Inhibitor ◽  
Temporal Inhomogeneity

The question is raised as to whether competitive inhibitors should block responses of tissue to nerve-released neurotransmitter to the same extent as they block equivalent responses to exogenous agonist. From a simple dynamic model of synaptic events, which takes into account non-constancy of transmitter concentration in space and time, it is deduced that equal blockade of responses to nerve-released and exogenous transmitter substance will occur if: (i) there are locally many more receptor molecules than transmitter molecules; (ii) the active agonist–receptor complex, A n R, has n = 1 ; and (iii) tissue response is insensitive to spatial or temporal inhomogeneity of AR. In such a case there will also be equal sensitivity of responses to other modes of inhibition: irreversible competitive, uncompetitive, and non-competitive. Equal blockade of responses to equi-effective endogenous and exogenous agonist will also occur if nerve stimulation gives rise to a steady uniform concentration of agonist, so that equilibrium kinetics are applicable. When n > 1 and/or when tissue responses reflect local peak A n R, response to nerve-released transmitter will be relatively insensitive to receptor blockade by a competitive inhibitor. The same is true for irreversible competitive blockade or for modulation of receptor density. However, an uncompetitive inhibitor (e. g. a ‘channel blocker’) may be more effective against nerve-released agonist than against exogenous agonist.

Protective effect of vanillin against carbon tetrachloride (CCl4)-induced oxidative brain injury in rats

2011 ◽  
Vol 28 (7) ◽  
pp. 655-662 ◽  
Author(s):  
Mohamed Makni ◽  
Yassine Chtourou ◽  
Mohamed Barkallah ◽  
Hamadi Fetoui
Keyword(s):  
Carbon Tetrachloride ◽  
Protective Effect ◽  
Brain Damage ◽  
Glutathione Transferase ◽  
Single Injection ◽  
Male Rats ◽  
Control Group ◽  
Protective Effects ◽  
Degree Of Protection ◽  
Oxidative Brain Injury

This study investigated the protective effects of vanillin against acute brain damage induced by carbon tetrachloride (CCl4) in rats. The study was performed on 32 male rats divided into four groups: a control group, vanillin group ([Va] 150 mg/kg/day, intraperitoneally [i.p.]) and CCl4 toxication groups received a single injection of CCl4 (1 ml/kg, i.p.; CCl4 and Va + CCl4 groups). The degree of protection in brain tissue was evaluated by the levels of malondialdehyde (MDA), glutathione (GSH), superoxide dismutase, glutathione transferase, glutathione peroxidase and nitric oxide (NO). Vanillin showed a significant brain-protective effect by decreasing the level of lipid peroxidation and NO2 and elevated the activities of antioxidative enzymes and level of GSH. Consequently vanillin blocked oxidative brain damage induced by CCl4 in rats.

Effect of Human Plasma Proteins on Stabilisation of Platelet Anti-Aggregatory Activity of Prostacyclin

1982 ◽  
Vol 19 (4) ◽  
pp. 241-244 ◽  
Author(s):  
D P Mikhailidis ◽  
A M Mikhailidis ◽  
P Dandona
Keyword(s):  
Biological Activity ◽  
Fatty Acid ◽  
Protective Effect ◽  
Clinical Relevance ◽  
Plasma Proteins ◽  
Human Albumin ◽  
Albumin Solution ◽  
Degree Of Protection ◽  
Buffer Solutions ◽  
Human Albumin Solution

Following the demonstration that biological activity of prostacyclin is more stable in plasma than in buffer solutions at physiological pH, we investigated the possibility that a plasma protein may be responsible for this effect. The duration of platelet anti-aggregatory activity of prostacyclin in fatty acid-free human albumin solution was significantly longer than in buffer solutions. The duration of this ‘protection’ was proportional to the concentration of albumin; α, β, and γ-globulin preparations had no ‘protective’ effect. The degree of ‘protection’ by albumin solutions was lower than that by plasma despite identical albumin concentrations. This discrepancy may in part be explained by the tendency of plasma to become alkaline on standing, a change that would tend to stabilise prostacyclin. The clinical relevance of our findings is discussed.

scholarly journals Suicidal inactivation and labelling of ammonia mono-oxygenase by acetylene

1985 ◽  
Vol 227 (3) ◽  
pp. 719-725 ◽  
Author(s):  
M R Hyman ◽  
P M Wood
Keyword(s):  
Protective Effect ◽  
Gel Electrophoresis ◽  
Ammonia Oxidation ◽  
Polyacrylamide Gel Electrophoresis ◽  
Competitive Inhibitor ◽  
Ion Concentrations ◽  
First Order ◽  
First Order Kinetics ◽  
Labelling Experiment ◽  
Suicide Substrate

Acetylene brings about a progressive inactivation of ammonia mono-oxygenase, the ammonia-oxidizing enzyme in Nitrosomonas europaea. High NH4+ ion concentrations were protective. The inactivation followed first-order kinetics, with a rate constant of 1.5 min-1 at saturating concentrations of acetylene. If acetylene was added in the absence of O2, the cells remained active until O2 was re-introduced. A protective effect was also demonstrated with thiourea, a reversible non-competitive inhibitor of ammonia oxidation. Incubation of cells with [14C]acetylene was found to cause labelling of a single membrane polypeptide. This ran on dodecyl sulphate/polyacrylamide-gel electrophoresis with an Mr value of 28 000. It is concluded that acetylene is a suicide substrate for the mono-oxygenase. The labelling experiment provides the first identification of a constituent polypeptide of ammonia mono-oxygenase.

scholarly journals Evidence for an arginine residue at the coenzyme-binding site of Escherichia coli isocitrate dehydrogenase

1989 ◽  
Vol 261 (1) ◽  
pp. 301-304 ◽  
Author(s):  
J S McKee ◽  
H G Nimmo
Keyword(s):  
Escherichia Coli ◽  
Binding Site ◽  
Isocitrate Dehydrogenase ◽  
Arginine Residue ◽  
Order Process ◽  
First Order ◽  
Coenzyme Binding ◽  
Phosphorylated Form ◽  
Specific Reagent ◽  
Coenzyme Binding Site

The arginine-specific reagent phenylglyoxal inactivated the active, dephosphorylated, form of Escherichia coli isocitrate dehydrogenase rapidly in a pseudo-first-order process. Both NADP+ and NADPH protected the enzyme against inactivation. Phenylglyoxal appeared to react with one arginine residue per subunit, and the extent of the reaction was proportional to the extent of the inactivation. In contrast, the phosphorylated form of isocitrate dehydrogenase did not react detectably with phenylglyoxal. The data indicate that the coenzyme-binding site of isocitrate dehydrogenase contains a reactive arginine residue that is protected by phosphorylation, and are consistent with the hypothesis that phosphorylation of the enzyme occurs close to or at its active site.

scholarly journals Red blood cell tension controlsPlasmodium falciparuminvasion and protects against severe malaria in the Dantu blood group

2018 ◽  
Author(s):  
Silvia N. Kariuki ◽  
Alejandro Marin-Menendez ◽  
Viola Introini ◽  
Benjamin J. Ravenhill ◽  
Yen-Chun Lin ◽  
...  
Keyword(s):  
Protective Effect ◽  
Severe Malaria ◽  
Blood Group ◽  
Sickle Cell ◽  
Sickle Cell Trait ◽  
Surface Protein ◽  
Major Effect ◽  
Similar Degree ◽  
Parasite Invasion ◽  
Degree Of Protection

Malaria has had a major effect on the human genome, with many protective polymorphisms such as sickle cell trait having been selected to high frequencies in malaria endemic regions1, 2. Recently, we showed that a novel blood group variant, Dantu, provides 74% protection against all forms of severe malaria in homozygous individuals3-5. This is a similar degree of protection to sickle cell trait and considerably greater than the most advanced malaria vaccine, but until now the mechanism of protection has been unknown. In the current study, we demonstrate a significant impact of Dantu on the ability ofPlasmodium falciparummerozoites to invade RBCs. The Dantu variant was associated with extensive changes to the RBC surface protein repertoire, but unexpectedly the malaria protective effect did not correlate with specific RBC-parasite receptor-ligand interactions. By following invasion using video microscopy, we found a strong link between RBC tension and parasite invasion and, even in non-Dantu RBCs, identified a tension threshold above which RBC invasion did not occur. Dantu RBCs had higher average tension, meaning that a higher proportion of Dantu RBCs could not be invaded. These findings not only provide an explanation for the protective effect of Dantu against severe malaria, but also provide fresh insights into the essential process ofP. falciparumparasite invasion, and how invasion efficiency varies across the heterogenous populations of RBCs that are present both within and between individuals.

scholarly journals α-Glucosidase and α-Amylase Inhibitory Compounds from three African Medicinal Plants: An Enzyme Inhibition Kinetics Approach

2017 ◽  
Vol 12 (7) ◽  
pp. 1934578X1701200
Author(s):  
Mohammed Auwal Ibrahim ◽  
James Dama Habila ◽  
Neil Anthony Koorbanally ◽  
Md. Shahidul Islam
Keyword(s):  
Medicinal Plants ◽  
Competitive Inhibitor ◽  
Inhibitory Effect ◽  
Inhibition Kinetics ◽  
Lead Compounds ◽  
Inhibitory Compounds ◽  
Steady State Kinetic ◽  
Enzyme Inhibition Kinetics ◽  
State Kinetic ◽  
Uncompetitive Inhibitor

The quest to find new lead compounds with anti-diabetic effects via the inhibition of α-glucosidase and α-amylase had led us to conduct bioassay guided isolation of three African medicinal plants which resulted in the identification of bicyclo[2.2.0]hexane-2,3,5-triol (1), 3β- O-acetyl betulinic acid (2) and 2,7-dihydroxy-4 H-1-benzopyran-4-one (3), as the bioactive compounds. The compounds demonstrated a significant (P < 0.05) inhibitory effect on α-glucosidase and α-amylase activities than acarbose. Steady state kinetic analysis revealed that compounds 1 and 2 inhibited both α-amylase and α-glucosidase in non-competitive patterns whilst compound 3 was an uncompetitive inhibitor of α-glucosidase and a non-competitive inhibitor of α-amylase. In conclusion, the study has identified three new active α-glucosidase and α-amylase inhibitory compounds that could have the potential to retard postprandial hyperglycemia.

Relationships between inhibition constants, inhibitor concentrations for 50% inhibition and types of inhibition: new ways of analysing data

2001 ◽  
Vol 357 (1) ◽  
pp. 263-268 ◽  
Author(s):  
Antoni CORTÉS ◽  
Marta CASCANTE ◽  
María Luz CÁRDENAS ◽  
Athel CORNISH-BOWDEN
Keyword(s):  
Lactate Dehydrogenase ◽  
Malate Dehydrogenase ◽  
Competitive Inhibitor ◽  
Inhibitor Concentration ◽  
Catalysed Reaction ◽  
Pharmacological Studies ◽  
The Common ◽  
Uncompetitive Inhibitor ◽  
Cytosolic Malate Dehydrogenase ◽  
Theory And Experiment

The concentration of an inhibitor that decreases the rate of an enzyme-catalysed reaction by 50%, symbolized i0.5, is often used in pharmacological studies to characterize inhibitors. It can be estimated from the common inhibition plots used in biochemistry by means of the fact that the extrapolated inhibitor concentration at which the rate becomes infinite is equal to −i0.5. This method is, in principle, more accurate than comparing the rates at various different inhibitor concentrations, and inferring the value of i0.5 by interpolation. Its reciprocal, 1/i0.5, is linearly dependent on v0/V, the uninhibited rate divided by the limiting rate, and the extrapolated value of v0/V at which 1/i0.5 is zero allows the type of inhibition to be characterized: this value is 1 if the inhibition is strictly competitive; greater than 1 if the inhibition is mixed with a predominantly competitive component; infinite (i.e. 1/i0.5 does not vary with v0/V) if the inhibition is pure non-competitive (i.e. mixed with competitive and uncompetitive components equal); negative if the inhibition is mixed with a predominantly uncompetitive component; and zero if it is strictly uncompetitive. The type of analysis proposed has been tested experimentally by examining inhibition of lactate dehydrogenase by oxalate (an uncompetitive inhibitor with respect to pyruvate) and oxamate (a competitive inhibitor with respect to pyruvate), and of cytosolic malate dehydrogenase by hydroxymalonate (a mixed inhibitor with respect to oxaloacetate). In all cases there is excellent agreement between theory and experiment.

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