scholarly journals The reaction of amino-oxyacetate with pyridoxal phosphate-dependent enzymes

1978 ◽  
Vol 171 (3) ◽  
pp. 771-779 ◽  
Author(s):  
R A John ◽  
A Charteris
Keyword(s):  
Enzyme Activity ◽  
Pyridoxal Phosphate ◽  
Equilibrium Constants ◽  
Order Rate Constant ◽  
Bimolecular Reaction ◽  
Dopa Decarboxylase ◽  
Aspartate Transaminase ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

The carbonyl reagent amino-oxyacetate is frequently used in metabolic studies to inhibit individual pyridoxal phosphate enzymes. The reaction of this compound with three such enzymes, aspartate transaminase, 4-aminobutyrate transaminase and dopa (3,4-dihydroxyphenylalanine) decarboxylase, was studied to determine the extent to which the inhibition is reversible and the rates at which it takes place. Reactions were followed by observing changes in the absorption spectra of the bound coenzyme and by measuring loss of enzyme activity. The reactions with aspartate transaminase and aminobutyrate transaminase were not rapidly reversible and had second-order rate constants (21 degrees C) of 400 M-1.s.1 and 1300 M-1.s-1 respectively and all all concentrations studied showed the kinetics of a simple bimolecular reaction. The reaction with 4-aminobutyrate transaminase could not be reversed and that with aspartate transaminase could only be reversed significantly by addition of cysteinesulphinate to convert the enzyme into its pyridoxamine form. The first-order rate constant (21 degrees C) for the reverse reaction was 4 × 10(-5)s-1. Dopa decarboxylase inhibition by amino-oxyacetate was more rapid and more readily reversible, but measurements of rate and equilibrium constants were not obtained for this enzyme.

scholarly journals Compounds of 6, 13-Diamino-6, 13-Dimethyl-1, 4, 8, 11 - Tetraazacyclotetradecane

2021 ◽  
Author(s):  
◽  
Asokamali Siriwardena
Keyword(s):  
Rate Constants ◽  
Magnetic Measurements ◽  
Order Rate Constant ◽  
Acidic Solutions ◽  
First Order ◽  
Order Rate ◽  
Pendant Arm ◽  
Nickel Copper ◽  
13C Nuclear Magnetic Resonance ◽  
Kinetics Of

<p>The reaction of bis-(diaminoethane)nickel(II) chloride, ([Ni(en)2]Cl2 in methanol with formaldehyde and nitroethane in the presence of triethylamine proceeds readily to produce (6, 13-dimethyl-6, 13-dinitro-1, 4, 8, 11-tetraazacyclotetradecane)nickel(II) chloride, [Ni(dini)] - Cl2. Reduction of the nitro groups of this compound by catalytic hydrogenation yields three isomers of the pendant arm macrocyclic complex (6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazachyclotetradecane)nickel(II) chloride, designated a-, b- and c-[Ni(diam)]Cl2. These were separated by fractional crystallization. The aisomer was observed to isomerizes slowly in solution to the b- form. A parallel dissociation reaction of the a- isomer was also observed. The demetallation of a- and b- isomers of the diam complex of nickel by reaction with cyanide or concentrated acid at 140 degrees C produces the macrocycle meso-(6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazacyclotetra-decane), diam. A variety of hexamine, pentamine and tetramine complexes of diam with nickel(II), copper(II), cobalt(II) and (III), chromium(III), palladium(II), rhodium(III), zinc(II) and cadmium(II) were prepared. Hexamine and tetramine forms of labile metal complexes could be rapidly and reversibly interconverted by altering the pH. The hexamine cobalt(III) cation, [Co(diam)]3+ was by far the most inert of the prepared cobalt(III) complexes, remaining unaffected in hot acidic solutions. In contrast, a single pendant arm of the hexamine [Cr(diam)]3+ cation could be dissociated in acid. (Two possibly triamine complexes of lead were also prepared). These compounds were characterized by elemental analysis, magnetic measurements, electronic, infrared, 1H and 13C nuclear magnetic resonance spectra. The pendant arm protonation constants (log K) of diam and selected complexes of nickel, copper and palladium were calculated from potentiometric titration measurements at 25 degrees C. The log K values for diam at 25 degrees C (I = 0.1 M NaclO4) were 11.15, 9.7, 6.2 and 5.3. Kinetics of the parallel isomerization and dissociation of a-[Ni(dimH2)]4+ in HCl/NaCl solutions were monitored spectrophotometrically at 50 degrees C. The rate of reaction in acidic solutions showed a non-linear dependency on acid concentration. The observed first order rate constant (kobs) for disappearance of a-[Ni(diamH2)]4+ (by isomerization and dissociation) in 2.0 M HCl, 0.1 M NaOH and 2.0 M NaCl were 3.05 x 10-4, 2.0(3) x 10-2 and 5.0 x 10-5 s-1 respectively. The rate of the dissociation component of the reaction of a-[Ni(diamH2)]4+ in 2.0 M HCl at 50 degrees C was 1.82 x 10-7 s-1. Acid bydrolysis kinetics of (Cu[diamH2])(ClO4)4 in hydrochloric acid and perchloric acid at 50 and 70 degrees C were studied spectrophotometrically. The reactions were slow and the observed first order rate constants were to a first approximation independent of the particular acid or its concentration. The observed first order rate constants were 1 x 10-9 and 8 x 10-9 s-1 at 50 and 70 degrees C respectively. Questions about the nature of the reaction being followed have been raised.</p>

Kinetics of reconstitution of apotyrosinase by copper

1990 ◽  
Vol 68 (2) ◽  
pp. 476-479
Author(s):  
Donald C. Wigfield ◽  
Douglas M. Goltz
Keyword(s):  
Rate Constant ◽  
Copper Concentration ◽  
Copper Ions ◽  
Copper Ion ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Rate Limiting ◽  
Kinetics Of

The kinetics of the reconstitution reaction of apotyrosinase with copper (II) ions are reported. The reaction is pseudo first order with respect to apoenzyme and the values of these pseudo first order rate constants are reported as a function of copper (II) concentration. Two copper ions bind to apoenzyme, and if the second one is rate limiting, the kinetically relevant copper concentration is the copper originally added minus the amount used in binding the first copper ion to enzyme. This modified copper concentration is linearly related to the magnitude of the pseudo first order rate constant, up to a copper concentration of 1.25 × 10−4 M (10-fold excess), giving a second order rate constant of 7.67 × 102 ± 0.93 × 102 M−1∙s−1.Key words: apotyrosinase, copper, tyrosinase.

scholarly journals Inactivation of the endogenous argininosuccinate lyase activity of duck δ-crystallin by modification of an essential histidine residue with diethyl pyrocarbonate

1993 ◽  
Vol 293 (2) ◽  
pp. 537-544 ◽  
Author(s):  
H J Lee ◽  
S H Chiou ◽  
G G Chang
Keyword(s):  
Enzyme Activity ◽  
Rate Constant ◽  
Order Rate Constant ◽  
Histidine Residue ◽  
Argininosuccinate Lyase ◽  
First Order ◽  
Diethyl Pyrocarbonate ◽  
Order Rate ◽  
Lyase Activity ◽  
Pseudo First Order

The argininosuccinate lyase activity of duck delta-crystallin was inactivated by diethyl pyrocarbonate at 0 degrees C and pH 7.5. The inactivation followed pseudo-first-order kinetics after appropriate correction for the decomposition of the reagent during the modification period. The plot of the observed pseudo-first-order rate constant versus diethyl pyrocarbonate concentration in the range of 0.17-1.7 mM was linear and went through the origin with a second-order rate constant of 1.45 +/- 0.1 M-1.s-1. The double-logarithmic plot was also linear, with slope of 1.13, which suggested a 1:1 stoichiometry for the reaction between diethyl pyrocarbonate and delta-crystallin. L-Arginine, L-norvaline or L-citrulline protected the argininosuccinate lyase activity of delta-crystallin from diethyl pyrocarbonate inactivation. The dissociation constants for the delta-crystallin-L-arginine and delta-crystallin-L-citrulline binary complexes, determined by the protection experiments, were 4.2 +/- 0.2 and 0.12 +/- 0.04 mM respectively. Fumarate alone had no protective effect. However, fumarate plus L-arginine gave synergistic protection with a ligand binding interacting factor of 0.12 +/- 0.02. The double-protection data conformed to a random Uni Bi kinetic mechanism. Fluorescence-quenching studies indicated that the modified delta-crystallin had minimum, if any, conformational changes as compared with the native delta-crystallin. Inactivation of the enzyme activity was accompanied by an increasing absorbance at 240 nm of the protein. The absorption near 280 nm did not change. Treatment of the modified protein with hydroxylamine regenerated the enzyme activity to the original level. These results strongly indicated the modification of an essential histidine residue. Calculation from the 240 nm absorption changes indicated that only one histidine residue per subunit was modified by the reagent. This super-active histidine residue has a pKa value of approximately 6.8 and acts as a general acid-base catalyst in the enzyme reaction mechanism. Our experimental data are compatible with an E1cB mechanism [Raushel (1984) Arch. Biochem. Biophys. 232, 520-525] for the argininosuccinate lyase with the essential histidine residue close to the arginine-binding domain of delta-crystallin. L-Citrulline, after binding to this domain, might form an extra hydrogen bond with the essential histidine residue.

Kinetics of Reactions of 8-Quinolinol and Acetate with Hydroxyaluminum Species in Aqueous Solutions. 1. Polynuclear Hydroxyaluminum Cations

1971 ◽  
Vol 49 (10) ◽  
pp. 1683-1687 ◽  
Author(s):  
R. C. Turner ◽  
Wan Sulaiman
Keyword(s):  
Acetic Acid ◽  
Rate Constant ◽  
Empirical Equation ◽  
Decomposition Reaction ◽  
Order Rate Constant ◽  
Acetate Concentration ◽  
First Order ◽  
Order Rate ◽  
Pseudo First Order ◽  
Kinetics Of

The effect of varying 8-quinolinol and acetate concentration on the rate of decomposition of poly-nuclear hydroxyaluminum cations was studied. It was found that the concentration of the undissociated 8-quinolinol and acetic acid molecules determined the magnitude of the first order rate constant for the decomposition of the polynuclear hydroxyaluminum cations, except when the acetate concentrations were relatively high. With high acetate concentrations, it appeared that polynuclear acetate species were involved in the reactions. An empirical equation was developed showing the effect of 8-quinolinol and acetic acid molecule concentrations on the pseudo first order rate constant for the decomposition reaction.

Kinetics of glycoluril template-directed Claisen condensations and mechanistic implications

2002 ◽  
Vol 80 (5) ◽  
pp. 517-527 ◽  
Author(s):  
Mohammad Rahimizadeh ◽  
Karen Kam ◽  
Stephen I Jenkins ◽  
Robert S McDonald ◽  
Paul HM Harrison
Keyword(s):  
Uv Spectroscopy ◽  
Condensation Reaction ◽  
Order Rate Constant ◽  
Nucleophilic Attack ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Benzoyl Group ◽  
Excess Base ◽  
Kinetics Of

Eight N-acetyl-N-aroyl-glycolurils were prepared and found to undergo efficient tert-butoxide-promoted Claisen-like condensation between the two acyl moieties. The kinetics for formation of each of the N-(aroylacetyl)gly coluril products were monitored by UV spectroscopy. The reaction exhibited pseudo-first-order kinetics in substrate in the presence of excess base. For the parent benzoyl compound the observed first-order rate constant (kobs) was linearly dependent on the concentration of the base, tert-butoxide. A Hammett plot of the resulting apparent second-order rate constants (kapp) vs. σ for each of the eight aroyl derivatives was linear and had a positive ρ value 1.04 ± 0.04), demonstrating that the substituent on the aromatic ring exerts a significant effect upon the condensation reaction. The corresponding plot for three [D3]acetyl analogues was also linear, but the slope was reduced by 20% relative to the protonated compounds. The isotope effect (kHapp/kDapp) thus increased from 1.4 (benzoyl) to 2.6 (p-nitrobenzoyl). The results are consistent with a three-step mechanism in which both deprotonation of the acetyl entity and the ensuing nucleophilic attack of the resulting enolate on the benzoyl group are partially rate-determining steps. The tetrahedral intermediate thus produced rapidly collapses to the product. For the [D3]acetyl benzoyl derivative, exchange of substrate deuterium with solvent hydrogen due to reprotonation of the enolate intermediate occurs at a rate that is similar to that of condensation, but the enolate partitions towards the product when electron withdrawing groups are present in the aroyl ring. Thus, despite the presence of a large excess of co-solvent tert-butanol, the efficiency with which the enolate undergoes condensation remains high. The clean kinetics observed allows further exploration of the details of this intramolecular Claisen-like condensation process.Key words: Claisen condensation, glycoluril, kinetics, Hammett, mechanism.

Kinetics of Exchange of Dimethylsulfoxide between Hexakis(dimethylsulfoxide)chromium(III) and Solvent: Pressure Effect and Mechanism

1973 ◽  
Vol 51 (22) ◽  
pp. 3795-3798 ◽  
Author(s):  
Debra Lynn Carle ◽  
Thomas Wilson Swaddle
Keyword(s):  
Rate Constant ◽  
Pressure Effect ◽  
Order Rate Constant ◽  
First Order ◽  
Order Rate ◽  
Kinetics Of

For the exchange of all six dimethylsulfoxide (DMSO) ligands in Cr(DMSO)63+ with perdeuterated DMSO solvent, the first-order rate constant (75°) = 5.5 × 10−5 s−1, while ΔH* = 23.1 kcal mol−1, ΔS* = − 11.8 cal deg−1 mol−1, and ΔV* = − 11.3 cm3 mol−1. These and other data are indicative of an associative interchange mechanism for substitution in Cr(III) DMSO complexes in DMSO.

Oxidation of the mercurous ion by peroxidase

1986 ◽  
Vol 64 (5) ◽  
pp. 969-972 ◽  
Author(s):  
Donald C. Wigfield ◽  
Season Tse
Keyword(s):  
Elemental Mercury ◽  
Order Rate Constant ◽  
Kinetics Of Oxidation ◽  
First Order ◽  
Order Rate ◽  
First Order Kinetics ◽  
Cold Vapour ◽  
Pseudo First Order ◽  
Kinetics Of ◽  
Mercurous Ion

The kinetics of oxidation of the mercurous ion by peroxidase have been measured by following the disappearance of mercurous ion using cold-vapour atomic absorption spectroscopy. Pseudo-first-order kinetics are observed with respect to mercurous ion, and the pseudo-first-order rate constants are linearly related to peroxidase concentration, showing first-order dependence on peroxidase. This behaviour is identical to oxidation of elemental mercury, and the second-order rate constant, 1.44 × 104 M−1 s−1 at 23 °C, is also, within experimental error, the same as that for elemental mercury oxidation. The data are interpreted in terms of peroxidase-induced disproportionation of the mercurous dimer, followed by two-electron oxidation of zero-valent mercury.

Compounds of 3,4,7,9,9,14,16-Octamethyl- (and 7,9,9,14,14,16-Hexamethyl-3,4-diphenyl) 1,2,5,6,10,13-Hexaazacyclohexadeca-2,4,6,16-tetraene With Nickel(II) and Copper(II). Preparations and Kinetics of Acid Hydrolysis Reaction

1988 ◽  
Vol 41 (11) ◽  
pp. 1665 ◽  
Author(s):  
NF Curtis
Keyword(s):  
Ground State ◽  
Metal Ion ◽  
Order Rate Constant ◽  
Singlet Ground State ◽  
Triplet Ground State ◽  
First Order ◽  
Order Rate ◽  
Ion Substitution ◽  
Kinetics Of ◽  
Hydrolysis Of

The complex nickel(II) cation of the bis-diazine macrocycle 3,4,7,9,9,14,14,16-octamethyl-1,2,5,6,10,13-hexaazacyclohexadeca-2,4,6,16-tetraene, omht, is formed by reaction of the complex of 3,3,9,9-tetramethyl-5,8-diazadodecane-2,11-dione dihydrazone with butane-2,3-dione, and the complex of the 7,9,9,14,14,16-hexamethyl-3,4-diphenyl homologue, bzht, is similarly prepared by reaction with 1,2- diphenylethane-1,2-dione. The cation [Cu(hmtd)]2+ is formed by metal ion substitution for a precursor of the nickel(II) cation. Compounds of the nickel(II) cations occur as singlet ground state perchlorate salts, or as triplet ground state octahedral compounds with additional ligands, e.g. [Ni(omht)(NCS)2], [{Ni(omht)(N3)}2](ClO4)2 and [Ni(omht)(en)] (ClO4)2. The singlet ground state [Ni(omht)]2+ cation in dimethyl sulfoxide converts into a triplet ground state species with first-order rate constant of 2.1(2)×10-6 s-1 at 25°C, 5.1(2)×10-5 s-1 at 50°C. The cations are slowly hydrolysed by acid, and pseudo-first-order rate constants in 2 mol l-1 HCl/NaCl for hydrolysis of [Ni(omht)]2+ and [Cu(omht)]2+ at 25° and 50°C are reported. These are of the order of 10-5 (25°C), 10-4(50°C) s-1, with a non-linear dependence on [H+], and with the reactions faster for the nickel(II) cation.

scholarly journals Inactivation of wheat-germ aspartate transcarbamoylase by the arginine-specific reagent phenylglyoxal

1986 ◽  
Vol 233 (1) ◽  
pp. 303-306 ◽  
Author(s):  
S C Cole ◽  
P A Yaghmaie ◽  
P J Butterworth ◽  
R J Yon
Keyword(s):  
Wheat Germ ◽  
Order Rate Constant ◽  
Bimolecular Reaction ◽  
Arginine Residue ◽  
Aspartate Transcarbamoylase ◽  
Carbamoyl Phosphate ◽  
Active Centre ◽  
First Order ◽  
Degree Of Protection ◽  
Order Rate

Wheat-germ aspartate transcarbamoylase (EC 2.1.3.2) was inactivated by phenylglyoxal in a first-order process, provided that the inactivation time did not exceed 10 min. Apparent first-order rate constants were linearly dependent on phenylglyoxal concentration, indicating a bimolecular reaction between a single active-centre residue and phenylglyoxal, with second-order constant of 0.023 mM-1 X min-1. A plot of apparent first-order rate constant versus pH showed a steep rise above pH 9.5, indicating that the essential residue has a pKa value of 10.5 or higher, consistent with an arginine residue. Saturating concentrations of the following ligands provided a degree of protection (percentages in parentheses) against 1 mM-phenylglyoxal: N-phosphonoacetyl-L-aspartate, a bisubstrate analogue (94%); carbamoyl phosphate (75%); UMP, an end-product inhibitor (53%). Succinate (an analogue of L-aspartate) alone gave no protection, but in combination with carbamoyl phosphate raised the protection to 92%, in agreement with the known binding order of the two substrates. These results indicate that the essential arginine residue is close to the carbamoyl phosphate site, probably oriented towards the aspartate site. Attempts to desensitize the UMP-binding site by reaction with phenylglyoxal, while protecting the active centre, were unsuccessful. The essential active-centre arginine residue is compared with a similar residue in the Escherichia coli enzyme.

scholarly journals Compounds of 6, 13-Diamino-6, 13-Dimethyl-1, 4, 8, 11 - Tetraazacyclotetradecane

2021 ◽  
Author(s):  
◽  
Asokamali Siriwardena
Keyword(s):  
Rate Constants ◽  
Magnetic Measurements ◽  
Order Rate Constant ◽  
Acidic Solutions ◽  
First Order ◽  
Order Rate ◽  
Pendant Arm ◽  
Nickel Copper ◽  
13C Nuclear Magnetic Resonance ◽  
Kinetics Of

<p>The reaction of bis-(diaminoethane)nickel(II) chloride, ([Ni(en)2]Cl2 in methanol with formaldehyde and nitroethane in the presence of triethylamine proceeds readily to produce (6, 13-dimethyl-6, 13-dinitro-1, 4, 8, 11-tetraazacyclotetradecane)nickel(II) chloride, [Ni(dini)] - Cl2. Reduction of the nitro groups of this compound by catalytic hydrogenation yields three isomers of the pendant arm macrocyclic complex (6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazachyclotetradecane)nickel(II) chloride, designated a-, b- and c-[Ni(diam)]Cl2. These were separated by fractional crystallization. The aisomer was observed to isomerizes slowly in solution to the b- form. A parallel dissociation reaction of the a- isomer was also observed. The demetallation of a- and b- isomers of the diam complex of nickel by reaction with cyanide or concentrated acid at 140 degrees C produces the macrocycle meso-(6, 13-diamino-6, 13-dimethyl-1, 4, 8, 11-tetraazacyclotetra-decane), diam. A variety of hexamine, pentamine and tetramine complexes of diam with nickel(II), copper(II), cobalt(II) and (III), chromium(III), palladium(II), rhodium(III), zinc(II) and cadmium(II) were prepared. Hexamine and tetramine forms of labile metal complexes could be rapidly and reversibly interconverted by altering the pH. The hexamine cobalt(III) cation, [Co(diam)]3+ was by far the most inert of the prepared cobalt(III) complexes, remaining unaffected in hot acidic solutions. In contrast, a single pendant arm of the hexamine [Cr(diam)]3+ cation could be dissociated in acid. (Two possibly triamine complexes of lead were also prepared). These compounds were characterized by elemental analysis, magnetic measurements, electronic, infrared, 1H and 13C nuclear magnetic resonance spectra. The pendant arm protonation constants (log K) of diam and selected complexes of nickel, copper and palladium were calculated from potentiometric titration measurements at 25 degrees C. The log K values for diam at 25 degrees C (I = 0.1 M NaclO4) were 11.15, 9.7, 6.2 and 5.3. Kinetics of the parallel isomerization and dissociation of a-[Ni(dimH2)]4+ in HCl/NaCl solutions were monitored spectrophotometrically at 50 degrees C. The rate of reaction in acidic solutions showed a non-linear dependency on acid concentration. The observed first order rate constant (kobs) for disappearance of a-[Ni(diamH2)]4+ (by isomerization and dissociation) in 2.0 M HCl, 0.1 M NaOH and 2.0 M NaCl were 3.05 x 10-4, 2.0(3) x 10-2 and 5.0 x 10-5 s-1 respectively. The rate of the dissociation component of the reaction of a-[Ni(diamH2)]4+ in 2.0 M HCl at 50 degrees C was 1.82 x 10-7 s-1. Acid bydrolysis kinetics of (Cu[diamH2])(ClO4)4 in hydrochloric acid and perchloric acid at 50 and 70 degrees C were studied spectrophotometrically. The reactions were slow and the observed first order rate constants were to a first approximation independent of the particular acid or its concentration. The observed first order rate constants were 1 x 10-9 and 8 x 10-9 s-1 at 50 and 70 degrees C respectively. Questions about the nature of the reaction being followed have been raised.</p>

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