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PubMed1981

Modulation by bicarbonate, phosphate, and maleate of the kinetics of adenosinetriphosphatase activity and of the binding of manganese ions to chloroplast coupling factor 1.

Bicarbonate, maleate, and phosphate were shown to modulate adenosinetriphosphatase (ATPase) activity in coupling factor 1 from chloroplasts. Kinetic analysis of the changes in the ratio between the apparent Km with and without effectors indicated that the stimulation of the activity by bicarbonate was a result of a decrease in the Km for MnATP2-. The inhibition by phosphate resulted from a decrease in the Ki for free ATP as a competitive inhibitor at pH 8. THe effectors did not change Vmax at this pH. However, at pH 6.5, both Km and Vmax of ATPase activity with MnATP2- were changed by maleate, yet the mode of inhibition by free ATP remained unaltered. In addition to decreasing the Km, bicarbonate induced a 10-fold decrease in the Kd for binding of Mn2+ at the two tight binding sites in the presence of ATP at pH 8. At pH 6.5, maleate also decreased both the Km for MnATP2- and the Kd for Mn2+ binding. A decrease in the Km of a substrate induced by an effector is likely to be a result of a decrease in the binding constant of the substrate. Therefore, these results are in harmony with the suggested assignment of the two tight binding sites of Mn2+ at the active sites of the enzyme.

Adenosine Diphosphate↗
PubMed2005

Mechanism of benzylsuccinate synthase: stereochemistry of toluene addition to fumarate and maleate.

Benzylsuccinate synthase catalyzes a highly unusual reaction: the addition of toluene to fumarate to form (R)-benzylsuccinic acid. The stereochemistry of this reaction has been examined using [d3-methyl]toluene and either fumarate or its cis stereoisomer, maleate, as the substrates. We demonstrate that when fumarate is the cosubstrate, deuterium is transferred from toluene to the C-3 pro-(R) position of benzylsuccinate, implying a syn addition of toluene to the double bond of fumarate. However, when maleate is the cosubstrate, the addition of toluene occurs in an anti fashion, so that deuterium transfer to the C-3 pro-(R) position of benzylsuccinate is also observed. This is consistent with the formation of the C-3 radical of benzylsuccinate as an intermediate, in which rotation about the C-2-C-3 bond can occur to relieve the sterically unfavorable cis conformation of the carboxylate groups when maleate is the cosubstrate.

Carbon-Carbon Lyases↗
PubMed2001

Development of NMR and raman spectroscopic methods for the determination of the degree of substitution of maleate in modified starches.

In this paper we report the application of NMR spectroscopy and Raman spectroscopy to determine the degree of maleate substitution in maleinated starches. Five kinds of maleinated starches were investigated and calibration sets were constructed to derive linear regression equations that may be used to predict the degree of maleate substitution for starch samples with unknown amounts of chemical modification. The calibration sets reported have very high linearity (r > 0.99) for both the NMR and Raman methods. The NMR and Raman calibration sets allow fast and nondestructive measurement of the degree of maleate substitution for different starches with little need of sample preparation.

Calibration↗
PubMed1982

[Are 0.1% timolol-maleate eyedrops suitable for treating chronic glaucoma? (author's transl)].

On the basis of 47 patients with chronic open-angle glaucoma, the administration of 0.1% timolol-maleate eye-drops was investigated in the form of a controlled long-term study over a period of 56 weeks. It was found that in a remarkable proportion of chronic glaucoma cases, this low concentration had an adequate, long-term effect, reducing IOP by 24-27%. The results obtained give sufficient grounds for the assumption that in the initial stages of glaucoma, the 0.1% solution is just as effective as solutions of a higher concentration, provided that a satisfactory degree of responsiveness to timolol-maleate is present from the outset. The local and systemic side-effects are relatively slight and therefore also fewer than with higher concentrations. Since in over 50% of patients with chronic glaucoma, 0.1% timolol-maleate eye-drops reduce IOP adequately over a considerable period of time, the 0.1% solution is to be recommended at all events for the initial treatment of glaucoma patients.

Chronic Disease↗
PubMed1996

Chronic dizocilpine maleate (MK-801) treatment suppresses the effects of nigrostriatal dopamine deafferentation on enkephalin but not on substance P expression in the rat striatum.

The present study examined the effects of chronic treatment with dizocilpine maleate (0.2 mg/kg i.p., twice a day for 8 days) alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic neurons on substance P and enkephalin expression in the rat striatum. This was done by means of quantitative in situ hybridization histochemistry and immunocytochemistry. As reported previously, the unilateral dopaminergic lesion resulted in marked decreases in substance P mRNA expression and immunoreactivity in the ipsilateral striatum while enkephalin mRNA expression and Met-enkephalin immunoreactivity were considerably increased in this structure. Blockade of NMDA receptors by chronic dizocilpine maleate treatment alone resulted in decreased levels of striatal substance P mRNA without significant change in substance P immunoreactivity versus controls. Enkephalin mRNA levels were also decreased in the striatum, matched by parallel reductions in Met-enkephalin immunoreactivity. These observations indicate that NMDA receptor activity may exert tonic excitatory effects on substance P and enkephalin expression in the striatum. The same chronic treatment with dizocilpine maleate started 12 days after the 6-hydroxydopamine injection suppressed the lesion-induced up-regulation of enkephalin expression without significantly affecting the down-regulation of substance P expression. These data provide evidence that NMDA receptor-mediated mechanisms contribute to the alteration of striatal enkephalin expression associated with dopaminergic depletion in hemiparkinsonian rat models.

Afferent Pathways↗
PubMed1969

Combined effect of sodium maleate and some thiol compounds on mercury excretion and redistribution in rats.

1. (+)-Penicillamine in a dose of 193 mumoles/kg given subcutaneously twice a day on the sixth and seventh days after the administration of 100 mug mercury increased the urinary excretion of rats more than the equimolar dose of N-acetyl-(+)-penicillamine but less than 2,3-dimercaptopropanol 48.3 mumoles/kg.2. Sodium maleate in a dose of 156 mumoles/kg given on the sixth and seventh days after the mercury did not influence mercury excretion or redistribution. Sodium maleate in the same dose increased considerably the effect of (+)-penicillamine on the urinary excretion and redistribution of mercury. It increased the effect of N-acetyl-(+)-penicillamine only slightly. There was a tendency to decrease the effect of 2,3-dimercaptopropanol.3. All the complexing agents decreased the kidney content of mercury and increased the liver and blood concentration of mercury. These changes were highest with 2,3-dimercaptopropanol. The combination of sodium maleate with (+)-pencillamine caused higher mercury excretion and lower kidney content but a smaller increase in the liver and blood mercury contents than 2,3-dimercaptopropanol.

Animals↗
PubMed1987

Inhibition of Clostridium botulinum 62A by fumarates and maleates and relationship of activity to some physicochemical constants.

A series of n-monoalkyl maleates and n-mono-, di-, and methyl n-alkyl fumarates were prepared, 18 esters of each, with R = CH3 to C18H37. Their activity against Clostridium botulinum was determined in culture medium. The n-monoalkyl maleates and fumarates possessed significant activity, particularly those esterified with higher C13 to C18 alcohols. Somewhat lower activity was exhibited by methyl n-alkyl fumarates, while symmetrical esters, di-n-alkyl fumarates, were almost inactive. An attempt was made to correlate the activity of n-monoalkyl maleates and fumarates with chain length, solubility in water, apparent dissociation constant (pKa'), and infrared and UV absorption frequencies. The active esters may have potential as preservatives in foods.

Chromatography, High Pressure Liquid↗
PubMed1976

Effects of maleate on carbohydrate metabolism in rats.

Intraperitoneal administration of maleate produced an increase in blood alpha-ketoacid, acetoacetate, and free fatty acids. The effect of this treatment on blood glucose levels depended on whether the rats were fed or fasted. In fed rats it was accompanied by slight, transient hyperglycemia connected with depletion of liver glycogen stores. In fasted animals moderate hypoglycemia was observed. The in vivo conversion of various precursors into blood glucose was not inhibited, suggesting that maleate does not affect hepatic gluconeogenesis. Neither was a direct effect on liver glycogenolysis observed. On the other hand, maleate inhibited renal gluconeogenesis from various substrates and stimulated anerobic glycolysis in kidney cortical alices. The data are interpreted in terms of increased utilization and decreased production of glucose by the kidney followed by secondary changes in liver carbohydrate metabolism.

Animals↗
PubMed1998

Effect of desmethyl tirilazad, dizocilpine maleate and nimodipine on brain nitric oxide synthase activity and cyclic guanosine monophosphate during cerebral ischemia in rats.

The present study was designed to evaluate the effects of pretreatment with a combination of desmethyl tirilazad (21-aminosteroid) plus dizocilpine maleate (N-methyl-D-aspartate receptor antagonist) and nimodipine (calcium channel antagonist) on constitutive nitric oxide synthase (cNOS) activity and cyclic guanosine monophosphate (cGMP) levels in brain homogenates of rats subjected to global cerebral transient ischemia induced by bilateral clamping of the carotids for 30 min and reduction of arterial pressure (to 50-60 mm Hg) by intravenous infusion of trimethaphan (30 mg/kg). Our results show that cerebral ischemia produced an increase in cNOS activity and cGMP levels in brain homogenates. Pretreatment with desmethyl tirilazad or dizocilpine maleate or nimodipine individually significantly suppressed (p < 0.01) the increase in cNOS activity and cGMP levels induced by cerebral ischemia, which may be related to their neuroprotective effect. Similar results were obtained with pretreatment by a combination of desmethyl tirilazad plus dizocilpine maleate plus nimodipine.

Animals↗
PubMed2000

Molecular analysis of maleate cis-trans isomerase from thermophilic bacteria.

Several strains of thermophilic bacteria containing maleate cis-trans isomerase were isolated from soil samples and identified as Bacillus stearothermophilus, Bacillus circulans, Bacillus brevis, and Deleya halophila. The maleate cis-trans isomerase was purified and characterized from one of the isolated strains, B. stearothermophilus MI-102. The purified enzyme of strain MI-102 showed higher thermal stability than the enzyme of a mesophile, Alcaligenes faecalis IFO13111. The seven maleate cis-trans isomerase genes (maiA) of thermophile were cloned and sequenced. B. stearothemophilus MI-102 MaiA has 67% amino acid identity with A. faecalis MaiA. All eight amino acid sequences of maiA gene products had significant conserved regions containing cysteine residues, which were previously suggested to be involved in an active site of the enzyme. To probe the catalytic mechanism, three cysteine residues in the conserved regions of A. faecalis MaiA were replaced with serine by site-directed mutagenesis. The results suggest that Cys80 and Cys198 play important roles in the enzyme activity.

Alcaligenes↗
PubMed2001

Contributions of the substrate-binding arginine residues to maleate-induced closure of the active site of Escherichia coli aspartate aminotransferase.

Crystallography shows that aspartate aminotransferase binds dicarboxylate substrate analogues by bonds to Arg292 and Arg386, respectively [Jager, J, Moser, M. Sauder, U. & Jansonius, J. N. (1994) J. Mol. Biol., 239, 285-305]. The contribution of each interaction to the conformational change that the enzyme undergoes when it binds ligands via these residues, is assessed by probing mutant forms of the enzyme lacking either or both arginines. The probes used are NaH(3)BCN which reduces the cofactor imine, the reactive substrate analogue, cysteine sulfinate and proteolysis by trypsin. The unreactive substrate analogue, maleate, is used to induce closure. Each single mutant reacted only 2.5-fold more slowly with NaH(3)BCN than the wild-type indicating that charge repulsion by the arginines contributes little to maintaining the open conformation. Maleate lowered the rate of reduction of the wild-type enzyme more than 300-fold but had little effect on the reaction of the mutant enzymes indicating that the ability of this dicarboxylate analogue to bridge the arginines precisely makes the major contribution to closure. The R292L mutant reacted 20 times more rapidly with cysteine sulfinate than R386L but 5 x 10(4) times more slowly than the wild-type enzyme, consistent with the proposal that enzyme's catalytic abilities are not developed unless closure is induced by bridging of the arginines. Proteolysis of the mutants with trypsin showed that, in the wild-type enzyme, the bonds most susceptible to trypsin are those contributed by Arg292 and Arg386. Proteolysis of the next most susceptible bond, at Arg25 in the double mutant, was protected by maleate demonstrating the presence of an additional site on the enzyme for binding dicarboxylates.

Amino Acid Sequence↗
PubMed1990

[A study of renal leak of 99mTc-DMSA in maleate-treated rats by factor analysis].

To elucidate renal leak of 99mTc-dimercaptosuccinic acid (99mTc-DMSA) in maleate-treated rats, plasma amino acid levels and urinary excreted % doses of 99mTc-DMSA and 131I-ortho-iodohippurate (131I-OIH) were studied by factor analysis. 0.4 m mol of Na-maleate dissolved in 2 ml of saline was intraperitoneally injected twice at an interval of 20 hours. Four hours later after second injection, mixture of 99mTc-DMSA and 131I-OIH was injected from tail vein. Urine was collected 15 minutes later to calculate the excretion ratios. Then rats were sacrificed by decapitation and blood samples were taken by cardiac puncture to determine plasma levels of amino acids and their metabolites. Urinary excreted % doses of 99mTc-DMSA were 10.1 +/- 1.3% in control group (n = 5) and 10.6 +/- 4.9% in maleate-treated group (n = 10). Of the 10 treated rats, only 2 rats showed clearly increased excretion of 99mTc-DMSA (19.1% and 19.4% respectively and others ranged from 6.2% to 12.0%). Fifteen variables used for factor analysis consisted of the % doses of two kinds of radiopharmaceuticals and 13 kinds of the data of amino acids analysis. Statistical procedures were as follows. Varimax rotation was performed, two factors were extracted and factor scores for each rat were plotted to obtain scattergram. Interpretation of the results led to a hypothesis that renal leak of 99mTc-DMSA might be relevant to decreased glutamine metabolism.

Animals↗
PubMedDate not supplied

Comparative antihypertensive effects of enalapril maleate and hydrochlorothiazide, alone and in combination.

Enalapril maleate is an investigational oral prodrug whose hydrolyzed diacid metabolite is a potent angiotensin-converting enzyme inhibitor. Fourteen patients with mild to moderate hypertension were evaluated after receiving placebo, and two weeks of treatment with each of the following: enalapril maleate (20 mg b.i.d.), hydrochlorothiazide (25 mg b.i.d.), and the two in combination. In comparison to placebo, the magnitudes of the blood pressure reduction after enalapril and hydrochlorothiazide alone were comparable. The reduction in blood pressure following enalapril was evident throughout the 12-hour dosing interval. The combination of enalapril and hydrochlorothiazide resulted in a marked further reduction in blood pressure that was greater than that predicted from the responses to the individual drugs (P less than 0.05). Biochemical parameters confirmed inhibition of angiotensin-converting enzyme during enalapril treatment; serum angiotensin-converting enzyme activity proved an excellent monitor of compliance. Enalapril was generally well tolerated. Adverse effects included symptomatic hypotension in three patients when enalapril was first added to hydrochlorothiazide and hyperesthesia of the oral mucosa without a loss of taste in one patient on enalapril. Enalapril maleate alone and especially in combination with hydrochlorothiazide appears to be an effective, well-tolerated converting enzyme inhibitor with at least a 12-hour duration of action.

Adult↗
PubMed1975

Colorimetric determinations of chlorpheniramine maleate, ephedrine hydrochloride, and guaiacolsulfonate potassium in a cough syrup.

Colorimetric methods for the quantitative determinations of chlorpheniramine maleate, ephedrine hydrochloride, and guaiacolsulfonate potassium in a cough syrup containing color (amaranth) are reported. Chlorpheniramine maleate can be assayed using the cyanogen bromide method as reported in the literature. Ephedrine hydrochloride can be assayed using a dye method in which interference from chlorpheniramine maleate is taken into consideration. Guaiacolsulfonate potassium can be assayed by coupling it with 4-aminoantipyrine (the method is similar to the one for phenylephrine hydrochloride). All of the methods are simple, accurate, and precise. The application of the guaiacolsulfonate potassium assay method to commercial dosage forms is reported.

Antitussive Agents↗
PubMed1997

Thermodynamics of Adsorption of n -Alkanes on Maleated Wood Fibers by Inverse Gas Chromatography

The adsorption of n -heptane, n -octane, n -nonane, and n -decane on untreated wood fiber and wood fiber treated with maleated polypropylene was studied by inverse gas chromatography (IGC) at infinite dilution or zero surface coverage. The specific retention volume increased with increasing probe chain length, decreased with increasing column temperature, and increased with increasing maleated polypropylene concentration. The enthalpy of adsorption increased with increasing chain length of the probe vapors. The enthalpy of adsorption remained constant after the treatment of wood fiber. The London dispersive component of the surface free energy decreased with the column temperature and showed no dependency with either the type of wood fiber or the maleated polypropylene concentration.

Journal Article↗
PubMed1991

Reduced severity of oxygen-induced retinopathy in the newborn rat after topical administration of timolol maleate. A preliminary study.

The effects of timolol maleate on intraocular pressure (IOP) and the severity of retinopathy induced by exposure to 80% oxygen were studied in newborn Wistar rats. One drop of timolol maleate (0.25%) instilled in each eye twice a day for the first ten days of life substantially reduced intraocular pressure without significantly modifying arterial pressure. Forty percent of the ratlings treated in this way failed to develop oxygen-induced retinopathy (OIR) after exposure to 80% oxygen for the first five days of life; in the other 60% OIR was less severe than that seen in an identically oxygenated group that did not receive timolol. The authors hypothesize that the pharmacologically induced reduction in IOP may have attenuated the effects of the high concentrations of oxygen on the immature retinal vessels by improving the ocular perfusion pressure. The possibility that timolol maleate also exerts a direct action on the caliber of these vessels cannot be excluded.

Administration, Topical↗
PubMed1984

Short-term and long-term timolol maleate effects on corneal sensitivity.

The authors present data concerning the effect of timolol maleate on corneal sensitivity investigated with the Cochet-Bonnet aesthesiometer and with cotton wool wisps. Among 30 subjects with open-angle glaucoma, 15 subjects underwent a short-term trial with timolol maleate 0.50% in one eye, while 15 served in a long-term trial with timolol maleate 0.50% or 0.25% in both eyes. A light reduction in corneal sensitivity, which did not reach statistical significance, was found during timolol treatment. After discussing the possible explanations of this side effect, the authors advise monitoring this parameter during the therapy.

Adult↗
PubMed1988

The effects of perhexiline maleate on low density lipoprotein processing and cholesterol metabolism in cultured human fibroblasts.

The effects of perhexiline maleate (PM, Pexid) on low density lipoprotein (LDL) processing and cholesterol metabolism were investigated after a 24 h pretreatment with the drug. Perhexiline maleate increased LDL uptake in the range 10(-6) to 10(-5) M (180% of control for 10(-5) M), whereas LDL binding and degradation were not affected. Sterol synthesis from sodium acetate was enhanced by perhexiline maleate (X 2.2 for 10(-5) M), while cholesterol esterification with oleic acid was decreased (40% of control for 10(-5) M). These effects of perhexiline on cholesterol metabolism are specific, since the synthesis of triacylglycerols from sodium acetate is not affected and since the incorporation of oleic acid into triacylglycerols is much less impaired. The decreased cholesterol esterification is accompanied by a reduction of acylcoenzyme A-cholesterol-O-acyltransferase (ACAT) activity measured in vitro on cell extracts.

Cells, Cultured↗