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)

The guanylate cyclase activity of axoneme--basal apparatus complexes isolated from bovine retinal rods has been investigated. The Mg2+ and Mn2+ complexes of GTP4- serve as substrates. Binding of an additional mole of Mg2+ or Mn2+ per mole of enzyme is required. Among cations which are ineffective are Ca2+, Ni2+, Fe2+, Fe3+, Zn2+, and Co2+. The kinetics are consistent with a mechanism in which binding of Mg2+ or Mn2+ to the enzyme must precede binding of MgGTP or MnGTP. The apparent dissociation constants of the Mg--enzyme complex and the Mn--enzyme complex are 9.5 x 10(-4) and 1.1 x 10(-4) M, respectively. The apparent dissociation constants for binding of MgGTP and MnGTP to the complex of the enzyme with the same metal are 7.9 x 10(-4) and 1.4 x 10(-4) M, respectively. The cyclase activity is maximal and independent of pH between pH 7 and 9. KCl and NaCl are stimulatory, especially at suboptimal concentrations of Mg2+ or Mn2+. Ca2+ and high concentrations of Mg2+ and Mn2+ are inhibitory. Ca2+ inhibition appears to require the binding of 2 mol of Ca2+ per mol of enzyme. The dissociation constant of the Ca2--enzyme complex is estimated to be 1.4 x 10(-6) M2. The axoneme--basal apparatus preparations contain adenylate cyclase activity whose magnitude is 1--10% that of the guanylate cyclase activity.
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PMID:Guanylate cyclase of isolated bovine retinal rod axonemes. 4 May 95

Solutions of ampicillin, carbenicillin, methicillin, oxacillin, penicillin G, and cephalothin in 5% dextrose were analyzed by nickel(II)-catalyzed hydroxylaminolysis. The reactions of these antibiotics were complete within 20 min at room temperature. Under the analytical conditions, molar absorptivities of the ferric-hydroxamate complexes ranged from 830 to 1005 liters/mole/cm. Coefficients of variation for the analysis of these antibiotics in 5% dextrose were typically less than 3% at concentrations of 1 mg/ml. Oxacillin was analyzed by the same method in normal saline and/or lactated Ringer solutions. The method also was applied to the analysis of chloramphenicol in aqueous solutions. Only ampicillin showed a significant decrease in concentration in 48 hr.
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PMID:Colorimetric determination of penicillins and related compounds in intravenous solutions by nickel (II)-catalyzed hydroxamic acid formation. 51 76

Kinetic experiments were made with pepsin in the presence of Cu2+ ions and additional Fe2+, Ni2+ or Zn3+ ions as sulphates. As a parameter of the pepsin activity the turnover-rate curves were determined with haemoglobin as a substrate. An important activation of the pepsin was obtained by Cu2+ additions of 5-10(-4) mole/1. When Cu2+ and Fe2+ ions were added to the reaction mixture at the same time, an additive effect of both metal cations was observed. A competitive effect of both metal cations was found in the combination of Cu2+/Ni2+ ions. Zn2+ addition did not influence the activation of pepsin caused by Cu2+ ions.
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PMID:[Interactions between various transition elements in their effect on pepsin activity]. 79 2

Human carboxypeptidase A has been isolated from activated pancreatic juice by means of affinity chromatography employing the competitive inhibitor benzylsuccinic acid as an affinity ligand. The structural and functional features of the human and bovine enzymes are quite analogous. The molecular weights of human and bovine carboxypeptidases A are virtually identical, their amino acid compositions are similar, both contain 1 g-atom of zinc/mole, and the activities of both are restored by addition of zinc to the apoenzyme. The inhibition of human carboxypeptidase by chelating agent is reversed by either dilution or addition of a metal such as Cu2+. When other metals are substituted for the native zinc, peptidase activity of the human metallocarboxypeptidases follows the order: cobalt greater than nickel greater than manganese greater than cadmium, while the sequence for esterase activities is: manganese greater than cobalt = cadmium greater than nickel. The latter sequence differs from that observed for the bovine enzyme. Human carboxypeptidase A crystallizes after dialysis at low ionic strength. Hydrolysis of the dipeptide carbobenzoxyglycyl-L-phenylalanine and of the ester benzoylglycyl-L-alpha-hydroxy-beta-phenyllactate exhibits kinetic anomalies, but that of their longer homologues does not. Chemical modifications with tyrosine reagents alters esterase and peptidase activities. The affinity chromatographic method here described should greatly facilitate future studies of this enzyme from human and other sources.
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PMID:Purification and crystallization of human carboxypeptidase A. 93 22

A soluble [NiFe] hydrogenase has been partially purified from the obligate thermophilic sulfate-reducing bacterium Thermodesulfobacterium mobile. A 17% purification yield was obtained after four chromatographic steps and the hydrogenase presents a purity index (A398 nm/A277 nm) equal to 0.21. This protein appears to be 75% pure on SDS-gel electrophoresis showing two major bands of molecular mass around 55 and 15 kDa. This hydrogenase contains 0.6-0.7 nickel atom and 7-8 iron atoms per mole of enzyme and has a specific activity of 783 in the hydrogen uptake reaction, of 231 in the hydrogen production assay and of 84 in the deuterium-proton exchange reaction. The H2/HD ratio is lower than one in the D2-H+ exchange reaction. The enzyme is very sensitive to NO, relatively little inhibited by CO but unaffected by NO2-. The EPR spectrum of the native hydrogenase shows the presence of a [3Fe-4S] oxidized cluster and of a Ni(III) species.
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PMID:Partial purification and characterization of the first hydrogenase isolated from a thermophilic sulfate-reducing bacterium. 131 68

We have studied the current-carrying ability and blocking action of various divalent cations in the Ca channel of Lymnaea stagnalis neurons. Changing the concentration or species of the permeant divalent cation shifts the voltage dependence of activation of the Ca channel current in a manner that is consistent with the action of the divalent cation on an external surface potential. Increasing the concentration of the permeant cation from 1 to 30 mM produces a twofold increase in the maximum Ca current and a fourfold increase in the maximum Ba current; the maximum Ba current is twice the size of the maximum Ca current for 10 mM bulk concentration. Correcting for the changing surface potential seen by the gating mechanism, the current-concentration relation is almost linear for Ba2+, and shows only moderate saturation for Ca2+; also, Ca2+, Ba2+, and Sr2+ are found to pass through the channel almost equally well. These conclusions are obtained for either of two assumptions: that the mouth of the channel sees (a) all or (b) none of the surface potential seen by the gating mechanism. Cd2+ blocks Lymnaea and Helix Ca channels at concentrations 200 times smaller than those required for Co2+ or Ni2+. Ca2+ competes with Cd2+ for the blocking site; Ba2+ binds less strongly than Ca2+ to this site. Mixtures of Ca2+ and Ba2+ produce an anomalous mole fraction effect on the Ca channel current. After correction for the changing surface potential (using either assumption), the anomalous mole fraction effect is even more prominent, which suggests that Ba2+ blocks Ca current more than Ca2+ blocks Ba current.
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PMID:Permeation and interaction of divalent cations in calcium channels of snail neurons. 240 16

Zinc is essential to the catalytic activity of angiotensin converting enzyme. The enzyme contains one g-atom of zinc per mole of protein. Chelating agents abolish activity by removing the metal ion to yield the inactive, metal-free apoenzyme. Zinc does not stabilize protein structure since the native and apoenzymes are equally susceptible to heat denaturation. Addition of either Zn2+, Co2+, or Mn2+ to the apoenzyme generates an active metalloenzyme; Fe2+, Ni2+, Cu2+, Cd2+, and Hg2+ fail to restore activity. The activities of the metalloenzymes follow the order Zn greater than Co greater than Mn. The protein binds Zn2+ more firmly than it does Co2+ or Mn2+. Hydrolysis of the chromophoric substrate, furanacryloyl-Phe-Gly-Gly, by the active metalloenzymes is subject to chloride activation; the activation constant is not metal dependent. Metal replacement mainly affects Kcat with very little change in Km, indicating that the role of zinc is to catalyze peptide hydrolysis.
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PMID:The functional role of zinc in angiotensin converting enzyme: implications for the enzyme mechanism. 299 78

The reaction of a copper(II) or nickel(II) imidazolate complex (M[CBP-PHEN-4-CHO-Im]) with zinc(II)tetraphenylporphyrin (TPP) in toluene results in the formation of an imidazolate bridged heterobinuclear axial adduct. Conversion of the four-coordinated Zn(TPP) to the five-coordinated species is followed in the visible region between 700 and 500 nm. Isosbestic behavior is exhibited at 523, 556, 588, and 638 nm by solutions of Zn(TPP) to which varying amounts of the metal imidazolate complex are added, indicating the existence of an equilibrium between Zn(TPP) and its axial adduct. The products exhibit maxima beta and alpha bands at 566 and 606 nm, respectively, which are red-shifted from 548 and 588 nm for Zn(TPP) and yield epsilon alpha/epsilon beta ratios of 0.57 and 0.55 for the Ni(II) and Cu(II) adducts, respectively. The binding of the metal imidazolate complexes is thought to closely resemble that of N-methylimidazole, N-CH3Im, rather than imidazolate, owing to the close spectral similarities with the adduct of the former and significant differences from the latter. Formation constants were determined using the 548-nm beta band of Zn(TPP) in the 293-308 K range by the method of Rose and Drago. At 25 degrees C, K = 152,000 M-1 and 110,000 M-1 for the copper and nickel adducts, respectively. Comparison of these values to that of 54,100 M-1 for N-CH3Im indicates that the metal-imidazolate complexes are considerably more reactive. Van't Hoff plots for the two series are very similar with enthalpies of -41.9 and -43.3 kJ/mole respectively. The structural core of these complexes is similar to the imidazolate bridged model of cytochrome c oxidase in that they contain a metal imidazolate axially adducted to a metalloporphyrin.
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PMID:Imidazolate bridged heterobinuclear complexes of zinc(II)tetraphenylporphyrin. Modeling cytochrome c oxidase. 301 87

A soluble hydrogenase from the halophilic sulfate reducing bacterium Desulfovibrio salexigens, strain British Guiana (NCIB 8403) has been purified to apparent homogeneity with a final specific activity of 760 mumoles H2 evolved/min/mg (an overall 180-fold purification with 20% recovery yield). The enzyme is composed of two non-identical subunits of molecular masses 62 and 36 kDa, respectively, and contains approximately 1 Ni, 12-15 Fe and 1 Se atoms/mole. The hydrogenase shows a visible absorption spectrum typical of an iron-sulfur containing protein (A400/A280 = 0.275) and a molar absorbance of 54 mM-1cm-1 at 400 nm. In the native state (as isolated, under aerobic conditions), the enzyme is almost EPR silent at 100 K and below. However, upon reduction under H2 atmosphere a rhombic EPR signal develops at g-values 2.22, 2.16 and around 2.0, which is optimally detected at 40 K. This EPR signal is reminiscent of the nickel signal C (g-values 2.19, 2.16 and 2.02) observed in intermediate redox states of the well characterized D. gigas nickel containing hydrogenase and assigned to nickel by 61 Ni isotopic substitution (J.J.G. Moura, M. Teixeira, I. Moura, A.V. Xavier and J. Le Gall (1984), J. Mol. Cat., 23, 305-314). Upon longer incubation with H2 the "2.22" EPR signal decreases. During the course of a redox titration under H2, this EPR signal attains a maximal intensity around--380 mV. At redox states where this "2.22" signal develops (or at lower redox potentials), low temperature studies (below 10 K) reveals the presence of other EPR species with g-values at 2.23, 2.21, 2.14 with broad components at higher fields. This new signal (fast relaxing) exhibits a different microwave power dependence from that of the "2.22" signal, which readily saturates with microwave power (slow relaxing). Also at low temperature (8 K) typical reduced iron-sulfur EPR signals are concomitantly observed with gmed approximately 1.94. The catalytic properties of the enzyme were also followed by substrate isotopic exchange D2/H+ and H2 production measurements.
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PMID:Redox properties and activity studies on a nickel-containing hydrogenase isolated from a halophilic sulfate reducer Desulfovibrio salexigens. 301 50

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


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