The effect of agar on the inhibitory activities of fatty amines

It has been shown that Difco Bacto agar contains at least two factors which produce a 27 to 93% reduction in the inhibitory activities of 11 fatty amines. One of these factors can be extracted from the agar by treatment with distilled water.     

Prostaglandin H synthase kinetics. The effect of substituted phenols on cyclooxygenase activity and the substituent effect on phenolic peroxidatic activity.

A series of p- and m-substituted phenols were examined for their effect on the cyclooxygenase activity of prostaglandin H synthase in 0.1 M phosphate buffer at pH 8.0 and 25.0 +/- 0.1 degrees C. A biphasic response was observed. At low concentrations phenols stimulate, but at higher concentrations inhibit, cyclooxygenase activity. Both enhancement and inhibition are increased by phenolic substituents which are electron-donating, quantified by Hammett sigma constants, and hydrophobic, quantified by Hantsch tau constants. The same series of substituted phenols was also reacted with compound II of prostaglandin H synthase at 4.0 +/- 0.5 degrees C. The compound II data fit the Hammett rho sigma equation; no hydrophobicity factors are required. Phenols inhibit cyclooxygenase activity by interfering with the binding of arachidonic acid to compound I and by competing directly with arachidonic acid as reducing substrates for compound I. Phenols stimulate cyclooxygenase activity by acting as reducing substrates for compound II, thereby accelerating the peroxidatic cycle. Phenols also protect the enzyme from self-catalyzed inactivation, most likely by removing the free radical of prostaglandin G2 by reducing it to prostaglandin G2. Kinetic parameters Km and kcat for cyclooxygenase activity were determined in the presence of phenols. Identical values of Km (15.3 +/- 0.5 mM) and kcat (89 +/- 2 s-1) were obtained regardless of which phenol was employed. Therefore these represent the true Km and kcat values for cyclooxygenase activity.     

The inhibitory effect of vanadium oxoanions on the activity of copper-zinc superoxide dismutase

The inhibitory effect of vanadate species on the enzymatic activity of bovine copper-zinc superoxide dismutase has been investigated at different pH values and vanadium concentrations. A definite inhibitory effect, clearly related to the main negative charge of each of the vanadate solutions, has been found. The results suggest that the origin of the inhibitory effect may be similar to that found for the phosphate ion, i.e., a diminution of the effectiveness of the substrate electronic guidance mechanism by partial neutralization of the charges close to the active site. Under physiological conditions, the inhibitory effect of vanadate is somewhat smaller than the phosphate.     

Nature of the inhibitory effect of collagenase on phosphodiesterase activity

The level of phosphodiesterase (PDE) activity is lower in collagenase-isolated human fat cells than in adipose tissue fragments. The inhibition is not species-specific since collagenase also inhibits PDE in rat adipose tissue and bovine heart. In subcellular fractions from isolated fat cells, the PDE activities were lowest in the plasma membrane-enriched fractions and highest in the cytosolic fractions. This is opposite to PDE in subcellular fractions obtained from adipose tissue fragments. In dose-response experiments, collagenase inhibited particulate PDE to a much larger extent than it inhibited soluble PDE. The extracellular activities of PDE were completely eliminated by collagenase. Repeated washings or reincubation of the isolated fat cells did not restore the PDE activity. A purified collagenase with low specific protease activity reduced the PDE activity in isolated fat cells to a lesser extent than did a collagenase with high specific protease activities. Collagen and several protease inhibitors were ineffective in preventing the reduction of PDE after exposure to collagenase. It is concluded that nonspecific proteases in the collagenase preparations used for fat cell isolation interact with particulate and soluble PDE causing an irreversible inhibition of PDE activity in isolated fat cells. Of the various forms of PDE, plasma membrane-associated PDE seems most sensitive to collagenase.     

Alanine reverses the inhibitory effect of phenylalanine on acetylcholinesterase activity

The aim of this work was to evaluate, in vitro, the effect of L-alanine (Ala) on suckling rat brain acetylcholinesterase (AChE) and on eel Electrophorus electricus pure AChE inhibited by L-phenylalanine (Phe) as well as to investigate whether Phe or Ala is a competitive inhibitor or an effector of the enzyme. AChE activity was determined in brain homogenates and in the pure enzyme after 1 h preincubation with 1.2 mM of Phe or Ala as well as with Phe plus Ala. The activity of the pure AChE was also determined using as a substrate different amounts of acetylthiocholine. Ala reversed completely the inhibited AChE by Phe (18-20% in 500-600 microM substrate, p<0.01). Lineweaver-Burk plots showed that Vmax remained unchanged. However, Km was found increased with Phe (150%, p<0.001), decreased with Ala alone (50%, p<0.001) and unaltered with Phe plus Ala. It is suggested that: a) Phe presents a competitive inhibitory action with the substrate whereas Ala a competitive activation; b) Ala competition with Phe might unbind the latter from AChE molecule inducing the enzyme stimulation; c) Ala might reverse the inhibitory effect of Phe on brain AChE in phenylketonuric patients, if these results are extended into the in vivo reality.     

Mechanisms of the inhibitory effect of the stellate ganglion on cardiac activity

The mechanisms of cardiac activity inhibition caused by stimulation of the stellate ganglion were studied in acute experiments on 28 dogs and 37 cats and chronic experiments on 12 cats. It was shown that inhibition of cardiac activity is caused by stimulation of the parasympathetic fibers of the vagus, anastomozing with stellate ganglion branches and ingoing as part of these fibers to the heart. The hypothesis of change over of the sympathetic nerve fibers to the intracardial cholinergic neurons and the hypothesis of the cholinergic component in the mechanism of catecholamine release by the sympathetic nerve terminals was not confirmed. Therefore, the known Dale's principle as to that one neuron exerts its efferent effect with the aid of one transmitter is quite just. alpha-Adrenoreceptors does not produce any noticeable effect on cardiac activity.     

Investigation of Ca2+ inhibitory effect on cellulase activity

The Ca2+ effect on the activity of cellulase [beta-1-4-endoglucanase) is quantitatively estimated. Values of partial inhibition of the enzyme activity at different Ca2+ concentrations within 2-10 mM are determined. The type of inhibition is identified from the data on kinetic analysis. The values of substrate and inhibitory constants are calculated.     

The effect of concentration of phenols on their batch methanogenesis

The biodegradability of phenol and six other phenolic compounds (o-, m-, and p-cresol, 2-, 3-, and 4-ethylphenol) was examined in batch methanogenic cultures. The effect of concentration of these alkyl phenols on the anaerobic biodegradation of phenol was also evaluated. The inoculum used in this study was cultivated in a continuous flow laboratory fermenter with phenol as the primary substrate. Phenol, at initial concentrations as high to 1400 mg/L was completely degraded to methane and carbondioxide after 350 hours incubation. Complete degradation of m- and p-cresol was also observed while the ethylphenols and o-cresol were not significantly degraded.At initial concentrations exceeding 600 mg/L, phenol inhibited the phenol-degrading microorganisms but not the methanogens. At about 600 mg/L, cresols reduced the rate of phenol degradation to 50% of that observed in a control culture containing only 200 mg/L phenol. Ethylphenols were more inhibitory than cresols. Phenol degrading microorganisms were more susceptible to inhibition by cresols and ethylphenols than were the methanogens. The inhibitory effects of the three isomers of cresol and ethylphenol did not vary with the isomer but rather with the substituted functional group.     

The inhibitory effect of dinitrosyl iron complexes (NO donors) on myeloperoxidase activity

The effect of synthetic analogues of dinitrosyl mononuclear iron complexes (DNICs) with functional sulfur-containing ligands (NO donors) on the activity of myeloperoxidase (MPO) was studied, and their efficiency was evaluated. It was shown that the enzyme MPO is the molecular target of DNICs. It was found that six DNICs inhibited the activity of MPO and one compound potentiated it. The evaluation of their efficiency showed that two DNICs effectively inhibited the activity of MPO by 50% at IC₅₀ = 2 × 10^–4 M and IC₅₀ = 5 × 10^–7 M.     

The inhibitory effect of various indolyl amino acid derivatives on arginase activity in macrophages

Summary. Numerous indolyl amino acids and their derivatives inhibited arginase activity. The inhibition was found to be non-competitive, – at least partly – allosteric, and independent on manganese ions in the active site, and it cannot be explained by the dissociation of arginase homotrimers. Indole alone is weakly inhibitory; however, the presence of three-carbon side chains and their net charges is favorable for the inhibition. The binding of the inhibitory compounds caused only minor changes in the steric structure of arginase: a slight increase in α-helix content was detected by circular dichroism together with a decrease in parallel pleated sheet and β-turn sections. A slight alteration in the tertiary structure was also found using tryptophane fluorescence studies, but buried apolar side chains were not transposed to the protein surface. Computer studies that were performed did not provide additional structural information. Authors’ address: András Hrabák, Department of Medical Chemistry, Molecular Biology and Patho-biochemistry, Semmelweis University Medical School, Budapest, VIII. Puskin u. 9., H-1444 POB 260, Hungary     

The inhibitory effect of tetramethylethylene diamine on water soluble and membrane bound acetylcholinesterase activity

• 1.1. The inhibitory effect of N,N,N′,N′-tetramethylethylene diamine (TEMED) on water soluble (WSAChE) and membrane bound (MBAChE) acetylcholinesterase was investigated.
• 2.2. TEMED (0.5–4.0 mM) reversibly inhibited WSAChE activity (18–62%) and MBAChE (20–61%) in a concentration dependent manner.
• 3.3. The IC₅₀ being about 2.8 mM for WSAChE and 2.6 mM for MBAChE.
• 4.4. Lineweaver-Burk plots indicated that the nature of inhibition is noncompetitive for both water soluble and membrane bound acetylcholinesterase, with K_m values 68 μM and 123 μM respectively.
• 5.5. An Arrhenius plot showed that the transition temperature (TT) is unaffected in the presence of TEMED.
• 6.6. The activation energy was increased below and above TT in the case of WSAChE only.
• 7.7. On the basis of this behaviour of TEMED with AChE. it can be proposed that it can be used as an eluting agent for the bounded AChE to affinity ligand and may have beneficial action on the reactivatability of irreversibly-inhibited AChE due to its structure.
• 8.8. Moreover there is a possibility that it can be used as a therapeutic agent for the treatment of Alzheimer's disease, myasthenia gravia and glaucoma like some other inhibitors of AChE.

     

The effect of phenols on respiratory enzymes in seed germination

Low molecular weight phenolic compounds were identified in two soilswith different vegetative cover, Fagus sylvatica, L. andPinus laricio, Poiret, spp. calabrica, and were tested atdifferent concentrations on seed germination of Pinuslaricio, and on respiratory and oxidative pentose phosphate pathwayenzymes involved in the first steps of seed germination. The data obtained showthat there are marked differences in the phenolic acid composition of the twoinvestigated soils. All the phenolic compounds bioassayed inhibited seedgermination and those extracted from Pinus laricio soilwere particularly inhibitory. We also found that the non-germination of seedsisstrongly correlated to the inhibition of the activities of enzymes ofglycolysisand the oxidative pentose phosphate pathway.     

Novel inhibitory effect on 5-lipoxygenase activity by the anti-asthma drug montelukast

5-Lipoxygenase is the key enzyme in the biosynthesis of leukotrienes, powerful lipid mediators involved in inflammation, cell-cell communication, and other important physiological and pathological conditions. Particularly, cysteinyl-leukotrienes have been recognized as playing a significant role in the pathophysiology of asthma and potent and effective Cys-LT1 receptor antagonists have been developed for the treatment of this illness. Here we report that montelukast, a structural Cys-LT1 receptor antagonist, also exerts a substantial and apparently direct inhibitory effect on 5-lipoxygenase activity in vitro, at concentrations in the lower micromolar range, which are of potential therapeutic relevance. Thus, when human mast cells HMC-1 were stimulated with the Ca ionophore A23187 in the presence of montelukast (up to 100 microM) a substantial decline in 5-lipoxygenase biosynthesis was observed. Similar results were obtained in the rat mast cell-like RBL-1 cell model (IC50 congruent with 2.5 microM) and in human polymorphonuclear leukocytes. Moreover, montelukast directly inhibited human recombinant 5-lipoxygenase. Kinetic experiments revealed that the inhibition was of the non-competitive type, suggesting that montelukast binds a yet undefined allosteric site on 5-lipoxygenase. 5-Lipoxygenase inhibition by montelukast appears to be highly selective since the drug had no effects on other enzymes of the leukotriene cascade, viz. LTC4 synthase and LTA hydrolase.