Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Some alloys used in restorative dentistry may evoke an allergic contact stomatitis in certain persons. In order to protect patients from materials with undesired reactions, and considering corrosion characteristics of different alloys used, it is useful to devise an adequate patch test battery to include the most relevant metals. Dental alloys are composed of a combination of various metals. 12 different ions of frequent occurrence (Au3+, Pd2+, Zn2+, Mo6+, Sn2+, Ga3+, In3+, Co2+, Cr3+(6+), Ni2+, Fe2+(3+) and Si4+) were epicutaneously tested as the aqueous solution of the respective salt. The concentrations are given in g/100 ml and also in m.mole/l. The 12 different metal ion solutions were patch tested on patients in 3 groups: one group with a positive history of contact stomatitis (30 patients, group 1), one group with a positive history of contact dermatitis (16 patients, group 2), and a control group (17 persons, group 3). In contrast to the control group, a remarkable high percentage (11%) of positive skin reactions to Pd was found in groups 1 and 2. No allergic or irritant skin reactions were detected to Ga, Sn and Zn. No irritant reaction was observed at pH values as low as 1.5. In the case of SiCl4 (pH = 0.5), 41% positive irritant reactions were evoked. In the group with a positive history of contact dermatitis (group 1), a positive reaction was found more often (69%) than in the group with a positive history of contact stomatitis (30%) (group 2). The difference between these groups was mainly caused by reactions to Ni and Pd.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Test battery for metal allergy in dentistry. 370 61

Cryospectrokinetic studies of zinc and cobalt carboxypeptidase A disclosed two intermediates in the hydrolysis of both peptides and depsipeptides and furnished all the rate and equilibrium constants for the reaction scheme E + S in equilibrium ES1 in equilibrium ES2---E + P [Auld, D. S., Galdes, A., Geoghegan, K. F., Holmquist, B., Martinelli, R. A., & Vallee, B. L. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 5041-5045]. Since the ES2 intermediate is the predominate enzyme species present at steady state, its chemical nature is deducible from subzero chemical quench studies done after steady state is established. Extrapolation of the product concentration to zero time, [P0], measures the concentration of the enzyme species in which bond cleavage has occurred. For peptides, the [P0]values are zero, indicating that no product is generated prior to turnover and therefore the ES2 intermediate involves a complex between enzyme and intact peptide substrate. For depsipeptides, [P0] values are 1 mol of produce per mole of enzyme over the entire temperature range -20 to -50 degrees C, indicating cleavage of the ester bond occurs prior to the rate-limiting step so that ES2 is more properly denoted by EP1P2, where P1 and P2 are the substrates for the reverse reaction. The rate-limiting step for depsipeptides thus involves release of the products which may occur directly or through a mandatory conformational change followed by rapid product release.
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PMID:Elucidation of the chemical nature of the steady-state intermediates in the mechanism of carboxypeptidase A. 395 20

Apoenzyme prepared by removal of the 2 mol of Zn2+/mol from Aeromonas aminopeptidase is inactive. Addition of Zn2+ reactivates it completely, and reconstitution with Co2+, Ni2+, or Cu2+ results in a 5.0-, 9.8-, and 10-fold more active enzyme than native aminopeptidase, respectively. Equilibrium dialysis and spectral titration experiments with Co2+ confirm the stoichiometry of 2 mol of metal/mol. The addition of only 1 mol of metal/mol completely restores activity characteristic of the particular metal. Interaction between the two sites, however, causes hyperactivation; thus, addition of 1 mol of Zn2+/mol subsequent to 1 mol of Co2+, Ni2+, or Cu2+ per mole increases activity 3.2-, 42-, or 59-fold, respectively. The cobalt absorption spectrum has a peak of 527 nm with a molar absorptivity of 53 M-1 cm-1 for 1 mol of cobalt/mol, which increases to 82 M-1 cm-1 for a second cobalt atom and is unchanged by further addition of Co2+. Circular dichroic (CD) and magnetic CD spectra indicate that the first Co2+ binding site is tetrahedral-like and that the second is octahedral-like. Stoichiometric quantities of 1-butylboronic acid, a transition-state analogue inhibitor of the enzyme [Baker, J. O., & Prescott, J. M. (1983) Biochemistry 22, 5322], profoundly affects absorption, CD, and MCD spectra, but n-valeramide, a substrate analogue inhibitor, has no effect. These findings suggest that the tetrahedral-like site is catalytic and the other octahedral-like site is regulatory or structural.
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PMID:Spectral and kinetic studies of metal-substituted Aeromonas aminopeptidase: nonidentical, interacting metal-binding sites. 407 99

The relative efficacy of 14 chelating agents in alleviating acute cobalt (II) chloride (ip) intoxication has been determined. For a level of 0.70 mmol/kg ip of CoCl2 (slightly higher than its LD50), the ip administration of chelating agents at a 2:1 and 5:1 mole ratio resulted in a significant antidotal action for L-cysteine, N-acetyl-cysteine, L-histidine,glutathione,D,L-penicillamine, DMSA, DTPA and EDTA. For a level of 1.18 mmol/kg ip of CoCl2 (slightly higher than its LD99) only L-cysteine, N-acetylcysteine,glutathione, DMSA, DTPA and EDTA resulted in a significant enhancement of the survival rate. The therapeutic indices of these compounds were respectively: 8.3, 11.8, 10.9, 9.1, 20.5 and 26.4; with EDTA and DTPA being the most effective. However, due to their low toxicity, N-acetylcysteine and glutathione should be considered as possible alternatives.
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PMID:Comparison of antidotal efficacy of chelating agents upon acute toxicity of Co(II) in mice. 408 20

The low-spin cyanide complexes of three Co(II) carbonic anhydrases were investigated by electron paramagnetic resonance (e.p.r.) at 9 and 35GHz. Well-defined and closely axial spectra were obtained only in the absence of oxygen. Several mole equivalents of cyanide were required for complete formation of the complexes in frozen solution, although large excesses caused abstraction of the cobalt. Experiments with [(13)C]cyanide showed that the low-spin complexes contained two CN(-) groups in an environment similar to that of the in-plane ligands in [Co(CN)(5)](3-). A combined e.p.r. and spectrophotometric titration confirmed the presence of two CN(-) ligands. A 5-co-ordinate square pyramidal structure involving three protein ligands was proposed. The dicyanide complex could be oxygenated reversibly, producing a characteristic new e.p.r. spectrum. The O(2) molecule was thought to occupy the remaining octahedral metal site in a formally Co(III) species. The optical spectrum of the dicyanide lacked the prominent d-d bands of the high-spin monocyanide. Both e.p.r. and optical data indicated that the low-spin complex was formed much more fully in frozen solution than at room temperature. Differences in behaviour between the high- and low-activity enzymes suggested some variation in conformational flexibility at the metal binding site.
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PMID:Electron-paramagnetic-resonance studies on cobalt(II) carbonic anhydrase. Low-spin cyanide complexes. 437 90

A strain of Bacillus pumilus produced an extracellular pectic enzyme with polygalacturonic acid as the substrate. This enzyme, with optimal activity at pH 8.0 to 8.5, produced reaction products that strongly absorbed light at 232 nm, indicating the presence of a pectic acid trans-eliminase (PATE). Neither pectin esterase nor polygalacturonase was detected in the cell-free culture fluid. Chromatographic examination of the end products revealed the presence of large quantities of unsaturated oligouronides unlike those found with B. polymyxa. It was found that the PATE was produced extracellularly during the negative logarithmic death phase of the organism. The filtrate from sonically treated cells did not show any activity for PATE or hydrolases for lower oligogalacturonides at any time during the growth cycle. The enzyme was inducible. Pectin, National Formulary (NF) was the best inducer, followed by polygalacturonic acid and galacturonic acid. Enzyme activity was markedly stimulated by calcium and other divalent ions. Copper and cobalt ions were inhibitory. The partially purified enzyme showed no significant activity on pectin containing a high methoxyl content (96% esterified). However, pectin NF with a lower methoxyl content (68% esterified) was attacked to a degree by the partially purified and crude enzyme preparations. The initial rate of PATE activity increased up to 60 C, about 16-fold higher than that observed at room temperature. The activation energy was calculated as 12,183 cal/mole. A protective action of calcium chloride against heat inactivation of the PATE was observed. Degradation of polygalacturonic acid by this enzyme produced several unsaturated oligouronides soon after its addition to the substrate. The major endproduct was thought to be different from that of other known PATE enzymes. Paper chromatographic studies and viscosity measurements disclosed the random cleaving nature of the enzyme an endo-PATE.
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PMID:Purification and properties of an polygalacturonic acid trans-eliminase produced by Bacillus pumilus. 512 2

In spite of the considerable progress made in recent years toward the understanding of the chemistry and biological function of the cobalt-containing B(12) group of compounds, much of the information still is more descriptive than definitive in nature. In general terms, it is known that the free vitamin forms can function as methyl group carriers and that the 5'-deoxyadenosyl or coenzyme forms serve as hydrogen carriers; but the mechanism of these processes is not understood in detail. More systematic studies of the pure chemistry of these complex molecules containing a carbon-cobalt covalent bond are needed before the biochemist can interpret many of his observations on the enzyme-catalyzed reactions. Even in relatively simple solutions it is difficult to ascertain the state of oxidation of several of the vitamin forms, and these problems are compounded when the reactive thiol compounds and complex proteins of the biological systems also are present. For example, both vitamin B(12r) (the Co(2+) form) and corresponding analogs are known to disproportionate in solution to B(12s) (Co(1+)) and B(12a) (Co(3+)) under a variety of mild conditions (12, 57). This means that in the biological systems it is exceedingly difficult to ascertain the chemical nature of many B(12) intermediates and reaction products. The role of the protein moiety of the various B(12)-linked enzymes in the catalytic processes is little known as is, also, the mode of binding of the B(12) derivative to the protein. These types of questions perhaps can be answered eventually by the crystallographers, whose art is becoming increasingly sophisticated. Note added after preparation of manuscript. In contrast to the values given in Table 4 for the molecular weights of the two dissimilar protein moieties of glycerol dehydrase, a recent report (57a), gives a value of 188,000 for the molecular weight of a stable, catalytically inactive complex of 1 mole of hydroxocobalamin and 1 mole of the apoenzyme complex of glycerol dehydrase. The latter is presumed to contain one equivalent of each of the two dissimilar protein subunits. The original estimate of 240,000 as the molecular weight of the unstable sulfhydryl protein moiety (39) was undoubtedly made on partially aggregated material.
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PMID:Vitamin B 12. 554 47

The involvement of histidyl residues as potential ligands to the binuclear active-site copper of Neurospora tyrosinase was explored by dye-sensitized photooxidation. The enzymatic activity of the holoenzyme was shown to be unaffected by exposure to light in the presence of methylene blue; however, irradiation of the apoenzyme under the same conditions led to a progressive loss of its ability to be reactivated with Cu2+. This photoinactivation was paralleled by a decrease in the histidine content whereas the number of histidyl residues in the holoenzyme remained constant. Copper measurements of photooxidized, reconstituted apoenzyme demonstrated the loss of binding of one copper atom per mole of enzyme as a consequence of photosensitized oxidation of three out of nine histidine residues. Their sequence positions were determined by a comparison of the relative yields of the histidine containing peptides of photooxidized holo- and apotyrosinases. The data obtained show the preferential modification of histidyl residues 188, 193, and 289 and suggest that they constitute metal ligands to one of the two active-site copper atoms. Substitution of copper by cobalt was found to afford complete protection of the histidyl residues from being modified by dye-sensitized photooxidation.
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PMID:Histidine at the active site of Neurospora tyrosinase. 645 22

Beef liver dihydropyrimidine amidohydrolase has been purified to homogeneity using both an electrophoretic and a hydrophobic chromatographic method. The enzyme is a tetramer with a molecular weight of 226,000 g mol-1, a subunit molecular weight of 56,500 g mol-1, and contains 4 mol of tightly bound (Ks greater than or equal to 1.33 X 10(9) M-1) Zn2+ per mole of active enzyme. The enzyme appears to be a true Zn2+ metalloenzyme because there exists a direct proportionality between enrichment of Zn2+ and active enzyme during purification, there is an almost quantitative relationship between the loss of both enzyme activity and Zn2+ during 8-hydroxyquinoline-5-sulfonic acid treatment to form apoenzyme, Zn2+ and Co2+ reactivate dipicolinic acid-inhibited enzyme, and saturating concentrations of a substrate, dihydrothymine, protect against 8-hydroxyquinoline-5-sulfonic acid inhibition. EDTA does not inhibit the enzyme; however, 8-hydroxyquinoline-5-sulfonic acid, o-phenanthroline, and 2,6-dipicolinic acid cause a time-dependent loss in activity which follows pseudo-first-order kinetics. Analysis of the resulting kinetic data for these three chelators indicates that the reaction pathway involves the formation of an enzyme-Zn2+-chelator ternary complex which then dissociates to form apoenzyme and a Zn2+-chelator complex. Like other Zn2+ metalloenzymes, the enzyme is inhibited by a number of substituted sulfonamides. In the case of p-nitrobenzenesulfonamide, this inhibition is competitive in nature. Using the purified enzyme, kinetic constants were determined for a variety of dihydropyrimidines, ureidocarboxylic acids, and hydantoin substrates. Normal hyperbolic kinetics were observed for the hydrolysis of the cyclic compounds, but the cyclization of the ureidoacids showed biphasic kinetics and different values of Km can be estimated at either high or low concentrations of these substrates.
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PMID:Bovine liver dihydropyrimidine amidohydrolase: purification, properties, and characterization as a zinc metalloenzyme. 663 68

The putative metal coordinating ligand cyanide was used to study the effects of modifications of the metal coordination sphere on the spectral properties and catalytic activity of cobalt and zinc carboxypeptidases. The absorption spectra of Co2+-carboxypeptidase B in the presence of cyanide pointed to a direct interaction of the ligands with the metal. Gel-filtration experiments showed that the binding of one mole of ligand per mole of enzyme metal ion resulted in maximal spectral effects. Binding of cyanide to the metal ion as measured by absorption spectroscopy was inhibited by acetyl-L-arginine, a peptide pseudosubstrate, and by acetyl-D-arginine, a competitive peptide inhibitor. Addition of acetyl arginine to the enzyme-cyanide complex caused displacement of the ligand, as evidenced by the spectral parameters. Cyanide inhibited peptide hydrolysis in a partially noncompetitive manner, i.e. it did not prevent binding of the substrate to the enzyme but the enzyme-substrate-cyanide complex was hydrolyzed at a slower rate than the enzyme-substrate complex. The dissociation constant evaluated from kinetic studies for the binding of cyanide to Co2+-carboxypeptidase B was in good agreement with that obtained from spectral measurements. Hydrolysis of the ester analog of the basis peptide substrate was not affected by cyanide. Based on these data a model is proposed in which the peptide carboxyl group displaces the water molecule from the metal coordination sphere during catalysis without increasing the coordination number.
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PMID:Mechanistic implications of cyanide binding to carboxypeptidase B. 711 16


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