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PubMed1987

[Treatment with enalapril maleate in patients with arterial hypertension, pluri-metabolic syndrome and habitual snoring].

The effects of enalapril maleate were studied in a group of 6 patients with arterial hypertension, hypertensive cardiopathy, multiple metabolic disorders and habitual snoring. Earlier treatment with antihypertensive drugs (diuretics, antiadrenergics, calcium antagonists) had been suspended when a marked deterioration was noted in metabolic parameters and plasmatic electrolytes as well as extremely disturbed sleep. The latter is probably attributable to increased respiratory obstruction during the night as a result of the increased hypertonia of the muscles of the upper air ways due to low blood potassium as well as the central and peripheral effects of the antiadrenergic drugs. After the wash-out period there was a marked improvement in laboratory parameters that continued after treatment with enalapril maleate. In particular, apart from a further slight fall in blood cholesterol and uricaemia there was a statistically significant drop in triglyceride levels. The improvement in the laboratory parameters made it possible to reduce the doses of the drugs being taken for the metabolic disorders. A distinct improvement was also noted in the sleep disturbances especially the excessive drowsiness during the day. There was also a statistically significant drop in arterial, systolic, diastolic and mean blood pressure without any significant change in heart beat. The results indicate that enalapril maleate should be the treatment of choice for those patients in whom high blood pressure is accompanied by alterations to the main metabolic parameters and habitual snoring.

Aged↗
PubMed1987

Effects of enalapril maleate on blood pressure, renin-angiotensin-aldosterone system, and peripheral sympathetic activity in essential hypertension.

Recent experimental studies showed that inhibition of angiotensin II synthesis may reduce sympathetic activity as evaluated by plasma catecholamine assay, sharing in the antihypertensive effect of angiotensin converting enzyme (ACE) inhibitors. Fifteen patients with essential hypertension were studied. Blood pressure and heart rate were evaluated both at rest and after stressor laboratory tests, before and four hours after administration of 20 mg of enalapril maleate and on the 14th and 120th days of continued administration. At the same time, blood samples were drawn for determinations of plasma renin activity, ACE, angiotensin II, plasma aldosterone concentration, and plasma norepinephrine levels. Enalapril in a dosage of 20 mg/day significantly and progressively lowered systolic and diastolic blood pressure at rest, with maximal decreases observed on the 120th day of the study period (P less than 0.001). Heart rate at rest and after exercise showed no significant differences throughout the study period. Good blood pressure control was observed during stressor laboratory tests. The greatest impact of blood pressure was observed on the 120th day during dynamic exercise (mean blood pressure from 139 +/- 3.9 to 111.5 +/- 6.3 mmHg; P less than 0.01) and on the 14th day during the cold pressure test (mean blood pressure from 133.3 +/- 3.9 to 111.2 +/- 4.7 mmHg; P less than 0.005). A marked and persistent ACE inhibition and a gradual and progressive decrease of angiotensin II (from 12.42 +/- 2.15 to 5.45 +/- 1.68 pg/ml; P less than 0.005) characterized the humoral activity of enalapril maleate. Moreover, a significant decrease of plasma norepinephrine levels was observed during the follow-up period with maximal reduction on the 120th day (from 311 +/- 34 to 197 +/- 33 pg/ml; P less than 0.01). It has been demonstrated that the pressor effect of angiotensin II was blunted during exercise. Our hemodynamic and humoral results appear to confirm the hypothesis that enalapril maleate may reduce blood pressure by direct inhibition of ACE and of kininase II as well as by a decreased sympathetic output, which may be secondary to angiotensin II inhibition. These results agree with the recent experimental demonstration of a reduced sympathetic nervous response to nerve stimulation during ACE inhibition.

Adult↗
PubMed1987

Effect of flupirtine maleate on the nociceptive pathway, EEG, evoked potentials and polysynaptic reflexes in laboratory animals.

Flupirtine maleate (3, 6 and 10 mg/kg, i.v.) elevated the pain threshold following electrical stimulation of rabbit tooth pulp with a peak effect at 10 minutes, suggesting central analgesic activity. Codeine (1, 3 and 6 mg/kg, i.v.), but not zomepirac (3, 6 and 10 mg/kg, i.v.), was also effective. In the cat, electrical stimulation of the tooth pulp or the contralateral sciatic nerve (central and peripheral nociceptive pathways, respectively) results in evoked potentials (activation) in the midbrain (MRF), thalamus (VPL) and sensory cortex. Flupirtine maleate (1 mg/kg, i.v.) did not alter the evoked responses. But at 3 and 6 mg/kg, i.v. it effectively blocked activation in the MRF, VPL and sensory cortex, primarily following tooth pulp stimulation rather than after sciatic nerve stimulation, suggesting that flupirtine was a selective antagonist of the central nociceptive pathway. Furthermore, in the cat, flupirtine at 3 mg/kg, i.v. blocked cortical and hippocampal arousal (activation) following MRF stimulation. At 6 and 10 mg/kg it partially antagonized the linguomandibular reflex (central polysynaptic reflex) but had little or no effect on the flexor reflex (peripheral polysynaptic reflex). The results of these investigations demonstrate the central nervous system activity of flupirtine maleate.

Aminopyridines↗
PubMedDate not supplied

The physiological disposition and metabolism of enalapril maleate in laboratory animals.

N-[1-(S)-carboxy-3-phenylpropyl]-L-alanyl-L-proline (MK-422), is a potent angiotensin I-converting enzyme (ACE) inhibitor, but as a diacid is poorly absorbed in laboratory animals. Enalapril maleate, the monoethyl ester of MK-422, proved to be significantly better absorbed in both rats and dogs. Peak levels of radioactivity in plasma occurred in 30 min in rats and 2 hr in dogs after a single dose of 14C-enalapril maleate (1 mg/kg, po). Rats excreted 26% of the dose in the urine and 72% in the feces in 72 hr; dogs excreted 40% of the dose in the urine and 36% in the feces. After the intravenous dose, the presence of radioactivity in the feces of both species suggested that some biliary excretion had occurred. Absorption was estimated to be 34% in the rat and 61% in the dog. The major metabolite of enalapril maleate in dogs, accounting for 86% of the urine radioactivity, was identified as MK-422 by GC/MS. A procedure was developed for the quantitation of MK-422 and enalapril in plasma and urine by their inhibition of purified ACE. The assays showed that enalapril was absorbed intact in dogs and converted to MK-422 after absorption.

Absorption↗
PubMedDate not supplied

[Complications after perhexiline maleate and amiodarone chlorhydrate treatment in a same patient: hypoglycemia, polyneuritis and hyperthyroidism (author's transl)].

The authors report the case of a 65 year old man treated with amiodarone chlorhydrate since 4 years and perhexiline maleate since 15 months, admitted for constitutional symptoms with fever, neurologic troubles particularly polyneuritis and pronounced hypoglycemia. A diagnostic of hyperthyroidism was made and attributed to amiodarone. The hypoglycemia and the polyneuritis were related to perhexiline maleate as other signs presented by the patient. All the symptoms disappeared after discontinuation of the drugs. The complications secondary to maleate perhexiline administration are reviewed.

Aged↗
PubMedDate not supplied

X-ray powder diffraction data for selected drugs: furosemide, hydrochlorothiazide, naproxen, naproxen sodium, propranolol hydrochloride, and the halopheniramine maleates.

X-ray powder diffraction data for 9 commonly used drug substances are reported. The data for furosemide, hydrochlorothiazide, propranolol hydrochloride, dexchlorpheniramine maleate, and brompheniramine maleate have been indexed by reference to published crystal structure data. The racemic modifications of propranolol hydrochloride and brompheniramine maleate are shown to exist as racemic compounds rather than racemic mixtures.

Chlorpheniramine↗
PubMed1981

The effect of midazolam maleate and diazepam on intraocular pressure in adults.

The effect on intraocular pressure of induction of anesthesia with 8-chloro-6-(2-fluorophenyl)-1-methyl-4H-imidazol[1,5-a][1,4]benzodiazepine (midazolam, Ro 21-3981, Dormicum) as maleate or 7-chloro-1,3-dihydro-1-methyl-5-phenyl-(2H)-1,4-benzodiazepin-2-one (diazepam) has not previously been reported. We induced anesthesia in 30 patients, free of ophthalmologic disease and in good general health, with either midazolam maleate, diazepam or 5-ethyl-5-(1-methylbutyl)-2-thiobarbituric acid (thiopental). Ten patients were treated with each agent for induction. Intraocular pressure was measured with a hand-held Perkins applanation tonometer before induction, 1 and 3 min after induction, 1 min after succinylcholine, 1 mg/kg, and 1 min after tracheal intubation. A significant (p less than 0.001) decrease in intraocular pressure occurred after each induction agent both 1 and 3 min after induction. Also, after each agent, a significant rise in intraocular pressure compared with control occurred after succinylcholine and tracheal intubation. We conclude that midazolam maleate and diazepam reduce intraocular pressure to the same degree as thiopental and would be safe for procedures in which a fall in intraocular pressure is desirable; however, none of these drugs will protect against the rise in intraocular pressure seen following the administration of succinylcholine or tracheal intubation during a rapid sequence induction of general anesthesia.

Adult↗
PubMed1981

Antihypertensive effect of oral timolol maleate and hydrochlorothiazide once daily compared with hydrochlorothiazide once daily.

The efficacy and safety of timolol maleate combined with hydrochlorothiazide given once daily compared with hydrochlorothiazide given once daily to patients with hypertension was investigated in a double-blind, randomized study. Patients with uncomplicated, mild to moderate hypertension were admitted to the study. Ten patients received two tablets once daily of timolol maleate 10 mg and hydrochlorothiazide 25 mg (T/H). Nine patients received hydrochlorothiazide 25 mg (HCTZ). Blood pressure and pulse rate measurements and laboratory tests were performed after a six-week placebo baseline period and throughout the 12-week study. Mean supine systolic blood pressure decreased by 21-35 mm Hg for the T/H group and by 10-24 mm Hg for the HCTZ group. Mean supine diastolic blood pressure decreased by 15-22 mm Hg for the T/H group and by 10-13 mm Hg for the HCTZ group. Changes observed in the laboratory variables were not statistically significant between the two treatment groups. One patient in each group had an adverse experience considered unrelated to the drug, and no patient had to discontinue the drug therapy because of an adverse reaction. Although both drug regimens effectively and safely treated uncomplicated mild to moderate hypertension, the timolol maleate and hydrochlorothiazide combination had a greater antihypertensive effect.

Adult↗
PubMed1996

Effects of acepromazine maleate and phenoxybenzamine on urethral pressure profiles of anesthetized, healthy, sexually intact male cats.

OBJECTIVES: To evaluate the effects of 2 compounds with alpha adrenergic antagonist properties on the urethral pressures of anesthetized, healthy, sexually intact male cats, and to evaluate one of the compounds for effect on striated muscle. ANIMALS: 20 healthy, sexually intact male cats. PROCEDURE: Cats were anesthetized with halothane, and urethral pressure profilometry was performed before and after treatment. 125I-labeled alpha-bungarotoxin bound to nicotinic receptors of murine skeletal muscle was used in a competitive binding study with acepromazine maleate. RESULTS: Acepromazine maleate significantly decreased intraurethral pressures in the preprostatic (19%) and prostatic (21%) regions of the urethra. There was no effect on the postprostatic/penile segment. Acepromazine did not inhibit 125I-labeled alpha-bungarotoxin binding to nicotinic receptors in murine skeletal muscle. Phenoxybenzamine significantly decreased intraurethral pressures (14%) in the preprostatic region of the urethra only. CONCLUSIONS: Acepromazine maleate and phenoxybenzamine have effects on the smooth muscle of the urethra of healthy, male cats. Acepromazine has no effect on striated muscle. CLINICAL RELEVANCE: alpha-Adrenergic compounds may be used in the pharmacologic management of feline urinary tract disease.

Acepromazine↗
PubMed1996

[Treatment of premenstrual tension syndrome (PMS) with lisuride maleate].

The etiology of PMS has not yet been defined, although there are several theories among which it is reported that there is an increase in prolactine levels involved in it. The purpose of this study was to evaluate a dopamine receptor agonist (lisuride maleate), in the treatment of PMS. 35 patients between 19 and 35 years old were recruited in a prospective study design, with diagnosis of PMS and no other gynecological disorder ruled out clinical and ultrasonographic examination, women with no previous treatment and with no use of hormonal agents, these patients were treated for three months with lisuride maleate, 0.3 mg-day in a three dosage scheme per day, the following symptoms were evaluated: headaches, mastalgia, bloating, edema of lower extremities and myalgia in legs, as well as hormonal parameters before and after treatment with estrogens, progesterone, prolactine, luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone, which were prescribed in the luteal phase (day 21). Results obtained were: reduction of all symptoms scores versus pretreatment: Headache from 85.7 to 20%, mastalgia from 91.4 to 25%, bloating from 74.2 to 40%, edema in lower extremities from 85.7 to 30%, myalgia in legs, from 61 to 34%. The hormonal profile only showed changes in FSH, since the basal pretreatment level was found in 18.6 and the post-treatment value was 13.86, progesterone from 2.7 to 4.6 and prolactine from 7.74 to 6.82. We conclude the lisuride maleate is a good option to the PMS treatment, since a significative reduction of symptoms are induced and it is well tolerated.

Adult↗
PubMed1992

Effects of 3-methylcholanthrene or diethyl maleate on the hepatotoxicity of acetaminophen.

This report presents a set of investigations on the hepatotoxic action of acetaminophen (AA). Male mice of Balb C strain were given [3H]acetaminophen in doses of 100, 300 and 600 mg kg-1 with or without pretreatment with 3-methylcholanthrene (3MCh) or diethyl maleate (DEM). The results of this study show that AA administered in moderate doses brings about necrotic changes due to adduct formation with macromolecules. Adduct formation was inversely correlated with the level of glutathione. Both modifiers enhanced hepatic necrosis and lethality. Diethyl maleate exerted these effects without enhancing covalent binding to macromolecules, while 3MCh increased both adduct formation and lipid peroxidation.

Acetaminophen↗
PubMed1984

Proximal tubular HCO3-, H+ and fluid transport during maleate-induced acidification defect.

The mechanism of tubular acidification was studied in proximal tubular acidification defect induced in rats by acute parenteral infusion of maleate (200 mg/kg), which causes diuresis and bicarbonaturia. Proximal tubular bicarbonate reabsorption and H+ ion secretion were determined by stopped-flow microperfusion and measurement of luminal pH by Sb microelectrodes. Stationary pH increased in proximal tubule from 6.78 to 7.25 and bicarbonate reabsorption decreased from 1.32 to 0.51 nmol/cm2 X s. In these segments, mean cell PD fell from -66.6 to -20.2 mV, while Jv as estimated by the Gertz technique fell to 15% of controls. A similar impairment of acidification was observed during luminal and capillary perfusion with phosphate Ringer's. Since H+-ion efflux from the lumen was not significantly increased and both acidification and alkalinization half-times (t/2) were increased, no evidence for an increase in passive permeability for H+/HCO3- was obtained. The increased t/2 found during luminal perfusion with acid phosphate indicates, according to an electrical analog model, a reduction in pump series conductance. These results show that maleate affects both proximal Na+ and H+ transport; this effect may be ascribed to impairment of sodium-dependent transport systems in the brush-border membrane.

Acid-Base Equilibrium↗
PubMed2006

Detection of maleate-induced Fanconi syndrome by decreasing accumulation of 125I-3-iodo-alpha-methyl-L-tyrosine in the proximal tubule segment-1 region of renal cortex in mice: a trial of separate evaluation of reabsorption.

OBJECTIVE: Fanconi syndrome is a renal dysfunction characterized by various combinations of renal tubular transport dysfunction involving amino acids, glucose, protein and other substances. Most reabsorption of amino acids occurs in proximal renal tubule segment 1 (S1). The present study evaluated the possibility of early detection of drug-induced Fanconi syndrome, based on decreased renal accumulation of 125I-3-iodo-alpha-methyl-L-tyrosine (125I-IMT), an amino acid transport marker, in the S1 region of renal cortex. The present experimental model used maleate (MAL)-induced Fanconi syndrome in mice. Results were compared between 125I-IMT and 3 other clinical renal radiopharmaceuticals: 99mTc-2,3-dimercaptosuccinic acid (99mTc-DMSA); 99mTc-mercaptoacetylglycylglycylglycine (99mTc-MAG3); and 99mTc-diethylenetriaminepentaacetic acid (99mTc-DTPA). METHODS: Male ddY mice (age, 6 weeks; body weight, 25 g) were used to create a Fanconi model of renal dysfunction. A single dose of maleate disodium salt was administered by intraperitoneal injection (6 mmol/kg). Hematoxylin and eosin (HE) staining of the renal cortex, renal autoradiography and measurement of renal radioactivity of labeled compounds were performed at 30, 60, 90 and 120 min after MAL injection. At 5 min after injection of labeled compounds (18.5 kBq for accumulation experiment, 670 kBq for autoradiography), animals were sacrificed by ether overdose and kidneys were removed. For the accumulation experiment, radioactivity was measured using a well-type scintillation counter. For autoradiography, 20-microm sections of frozen kidney were used with Bio-Imaging Analyzer. RESULTS: At 30 min after MAL injection, HE staining showed pyknosis in some proximal tubule cells. At that time, accumulations of 125I-IMT and 99mTc-DMSA in the S1 region were approximately 67% and 55% of control levels (p < 0.005). MAL increased accumulation of 99mTc-DTPA in the S1 region, but had no effect on accumulation of 99mTc-MAG3 in the S 1 region. CONCLUSIONS: Decreased accumulation of 123I-IMT in the S1 region appears to represent a useful marker for detection of MAL-induced Fanconi syndrome. In future, we plan to assess the efficacy of using 125I-IMT to monitor renal dysfunction induced by nephrotoxic clinical drugs.

Absorption↗
PubMed1980

The in vivo effects of maleate on the cation-distribution in rat kidney metallothionein sub-fractions after induction by cadmium and/or mercury.

The metallothionein fractions, isolated by gel filtration from the kidneys of rats that have been dosed with Cd2+, Hg2+ or Cd2+ followed by Hg2+, yield very different elution profiles on ion-exchange chromatography. The metallothionein from Cd2+-treated animals is resolved into the isomethallothioneins I and II and a minor, less negatively-charged species (B), which contains Cd2+ and copper, but little Zn2+. The corresponding fraction from the kidneys of rats doses with Hg2+ yields five components, all of which contain Hg2+, Zn2+ and Cu, but in different ratios. Three of these compounds correspond in their elution characteristics from DE-cellulose with the above-mentioned isometallothioneins I and II and fraction B. The last of these, which also is rich in Cu, is the major Hg2+-binding component. The distribution of Hg2+ and of other cations between these five sub-fractions, but not the number of sub-fractions, is altered by Cd2+-pretreatment of the animals. Treatment of Cd2+-dosed rats with sodium maleate has no significant effect on the distribution of cations (Cd2+, Zn2+ and copper) amongst the renal metallothionein subfractions. The same treatment, applied to animals dosed with either Hg2+ only, or Cd2+ followed by Hg2+, causes the elimination of 70--75% of the Hg2+ from the metallothionein fraction. Loss occurs from all subfractions, but is greatest in subfraction B, which also loses copper. Whilst it is possible that Hg2+ may induce metallothionein and other metalloproteins in the kidney, Hg2+ appears to bind to both isometallothioneins I and II, when these are induced by Cd2+-pretreatment. The loss of Hg2+, but not of Cd2+, from these metalloproteins after treatment with sodium maleate may be related to differences in the relative binding affinities of the two cations for thionein and other cellular proteins.

Animals↗
PubMed1986

The effect of depletion of nonprotein sulfhydryls by diethyl maleate plus buthionine sulfoximine on renal uptake of mercury in the rat.

Rats pretreated with diethyl maleate (DEM, 3.37 mmol/kg, ip) and buthionine sulfoximine (BSO, 0.45 mmol/kg, ip) and subsequently given mercuric chloride (HgCl2, 0.014 mmol/kg, sc) had a significantly greater mortality rate over the 24 hr after injection than rats given only HgCl2 or HgCl2 following either DEM or BSO alone. Depletion of nonprotein sulfhydryls (NPSH) in the kidney significantly decreased mercury uptake in that organ. A similar effect was not seen in the liver despite marked depletion of NPSH. Similarly, there was a tendency for less in vitro mercury accumulation in renal cortical slices from rats made glutathione deficient by DEM + BSO compared to control, or rats made glutathione deficient by DEM or BSO alone. Depletion of nonprotein sulfhydryls by the combination of the depleting agents diethyl maleate plus buthionine sulfoximine (DEM + BSO) had a greater effect to alter organic ion accumulation in renal cortical slices than the agents alone. The higher mortality produced by mercuric chloride after DEM + BSO pretreatment may have been due to an increased availability of mercury in lethal concentrations at other organ sites. These data suggest the possible importance of NPSH in renal mercuric ion accumulation, but not in the liver.

Animals↗
PubMed1997

Quantitative autoradiography of 5-[3H]6-cyano-7-nitro-quinoxaline-2,3-dione and (+)-3-[3H]dizocilpine maleate binding in rat vestibular nuclear complex after unilateral deafferentation, with comparison to cochlear nucleus.

The distributions of non-N-methyl-D-aspartate and N-methyl-D-aspartate receptors in the rat vestibular nuclear complex were estimated by quantitative autoradiography of 5-[3H]6-cyano-7-nitro-quinoxaline-2,3-dione and (+)-3-[3H]dizocilpine maleate binding, respectively. The binding of 5-[3H]6-cyano-7-nitro-quinoxaline-2,3-dione in the vestibular nuclear complex was also compared with that in the cerebellar cortex and cochlear nucleus. Measurements were made in control rats and in rats with unilateral destruction of the inner ear and removal of the vestibular ganglion. Compared to the unlesioned side, 5-[3H]6-cyano-7-nitro-quinoxaline-2,3-dione binding in the lesioned-side vestibular nuclear complex was decreased significantly in all regions at two to four postoperative days. However, the bilateral asymmetry disappeared in most regions by 30 days. 5-[3H]6-Cyano-7-nitro-quinoxaline-2,3-dione binding increased in the molecular layer of the cerebellar cortex at 30 days after lesion, although there were no clear changes at two to seven days. 5-[3H]6-Cyano-7-nitro-quinoxaline-2,3-dione binding in the cochlear nucleus decreased on the lesioned side, compared to the unlesioned side, in regions receiving significant auditory nerve innervation, but increased in the molecular layer of the dorsal cochlear nucleus. (+)-3-[3H]Dizocilpine maleate binding in regions of the vestibular nuclear complex was reduced on the lesioned side, compared to the unlesioned side, after deafferentation, with the largest reductions usually at 30 postoperative days. It is suggested that: (i) non-N-methyl-D-aspartate receptors are involved in synaptic transmission for both vestibular and auditory nerve fibers, while the involvement of N-methyl-D-aspartate receptors is less certain; (ii) unilateral deafferentation of the vestibular nuclear complex can result in bilateral asymmetries for non-N-methyl-D-aspartate and N-methyl-D-aspartate receptors, which are most prominent at earlier and later survival times, respectively; and (iii) vestibular compensation may involve regulation of both non-N-methyl-D-aspartate and N-methyl-D-aspartate receptors in the vestibular nuclear complex and activation of non-N-methyl-D-aspartate receptor-related processes in cerebellar cortex.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1999

Structure of Thermus thermophilus HB8 aspartate aminotransferase and its complex with maleate.

The three-dimensional structures of pyridoxal 5'-phosphate-type aspartate aminotransferase (AspAT) from Thermus thermophilus HB8 and pyridoxamine 5'-phosphate type one in complex with maleate have been determined by X-ray crystallography at 1.8 and 2.6 A resolution, respectively. The enzyme is a homodimer, and the polypeptide chain of the subunit is folded into one arm, one small domain, and one large domain. AspATs from many species were classified into aminotransferase subgroups Ia and Ib. The enzyme belongs to subgroup Ib, its sequence being less than 16% identical to the primary sequences of Escherichia coli, pig cytosolic, and chicken mitochondrial AspATs, which belong to subgroup Ia whose sequences are more than 40% identical and whose three-dimensional structures are quite similar with the active site residues almost completely conserved. The first X-ray analysis of AspAT subgroup Ib indicated that the overall and the active site structures are essentially conserved between the AspATs of subgroup Ia and the enzyme of subgroup Ib, but there are two distinct differences between them. (1) In AspAT subgroup Ia, substrate (or inhibitor) binding induces a large movement of the small domain as a whole to close the active site. However, in the enzyme of subgroup Ib, only the N-terminal region (Lys13-Val30) of the small domain approaches the active site to interact with the maleate. (2) In AspAT subgroup Ia, Arg292 recognizes the side chain carboxylate of the substrate; however, residue 292 of the enzyme in subgroup Ib is not Arg, and in place of Arg292, Lys109 forms a salt bridge with the side chain carboxylate. The thermostability of the enzyme is attained at least in part by the high content of Pro residues in the beta-turns and the marked increase in the number of salt bridges on the molecular surface compared with the mesophilic AspAT.

Amino Acid Sequence↗
PubMed2005

Probing the low-barrier hydrogen bond in hydrogen maleate in the gas phase: a photoelectron spectroscopy and ab initio study.

The strength of the low-barrier hydrogen bond in hydrogen maleate in the gas phase was investigated by low-temperature photoelectron spectroscopy and ab initio calculations. Photoelectron spectra of maleic and fumaric acid monoanions (cis-/trans-HO(2)CCH=CHCO(2)(-)) were obtained at low temperatures and at 193 nm photon energy. Vibrational structure was observed for trans-HO(2)CCH=CHCO(2)(-) due to the OCO bending modes; however, cis-HO(2)CCH=CHCO(2)(-) yielded a broad and featureless spectrum. The electron binding energy of cis-HO(2)CCH=CHCO(2)(-) is about 1 eV blue-shifted relative to trans-HO(2)CCH=CHCO(2)(-) due to the formation of intramolecular hydrogen bond in the cis-isomer. Theoretical calculations (CCSD(T)/ aug-cc-pVTZ and B3LYP/aug-cc-pVTZ) were carried out to estimate the strength of the intramolecular hydrogen bond in cis-HO(2)CCH=CHCO(2)(-). Combining experimental and theoretical calculations yields an estimate of 21.5 +/- 2.0 kcal/mol for the intramolecular hydrogen bond strength in hydrogen maleate.

Chemical Phenomena↗