Oxidation Of L-leucine Research Articles

Os(VIII) accelerated oxidation of L-leucine by hexacyanoferrate(III) in CTAB micellar medium

The kinetics of Os(VIII) accelerated L-Leucine (L-Leu) oxidation in cetyltrimethylammonium bromide (CTAB) by hexacyanoferrate(III) [HCF(III)] was investigated by registering the decline in absorbance at 431 nm. Employing the pseudo-first-order condition, the reaction’s advancement has been examined as an indicator of [CTAB], [Os(VIII)], [OH−], [L-Leu], [HCF(III)], temperature, and ionic strength. The results show that [OH−], [CTAB], and [L-Leu] are the critical parameters with a discernible influence on reaction rate. L-Leu interacts with HCF(III) in a 1:2 ratio. The rate constant is independent of the [HCF(III)] and is merely used up to regenerate the Os(VIII) during the reaction. In the investigated concentration ranges of Os(VIII), [OH−], and [L-Leu], the reaction demonstrates first-order kinetics, but follows less than unit order at higher concentrations of L-Leu (more than 6.0 × 10−3 mole dm−3) and alkali (more than 0.4 mole dm−3). A positive salt effect is indicated by the linear rise in reaction rate with additional electrolytes. CTAB catalyzes the process substantially, and once at its peak at 7.0 × 10−4 mole dm−3, the rate remains constant as [CTAB] grows up to 8.5 × 10−4 mole dm−3. With anionic surfactant sodium dodecyl sulfate, the reaction rate was significantly reduced even in the presence of Os(VIII). Reduced repulsion between surfactant molecule’s positive charge heads brought on by the negative-charged HCF(III), OH−, and [OsO5(OH)]3− molecules may be responsible for the witnessed drop in CTAB critical micellar concentration (CMC).

Kinetics and Mechanistic Oxidation of ℓ-Leucine and ℓ-Valine by 1,3-Dichloro-5,5-dimethylhydantoin in Aqueous Acetic Acid Medium

Kinetics and Mechanistic Oxidation of ℓ-Leucine and ℓ-Valine by 1,3-Dichloro-5,5-dimethylhydantoin in Aqueous Acetic Acid Medium

Oxidative Degradation ofl-Isoleucine by Au3+Complexes in Weakly Acid Medium: A Kinetic and Mechanistic Investigation

Oxidative degradation of l-isoleucine (Ileu) by Au3+ complexes has been studied spectrophotometrically in weakly acid medium (acetic acid–sodium acetate buffer, pH range 3.72–4.80) in the temperature range 288–308 K. The reaction is first order with respect to AuIII but complex order (<1) with respect to isoleucine. Ionic strength has no significant effect on the reaction kinetics. Both H+ and Cl− ions have been found to show inhibiting effect on the reaction rate. Decreasing solvent polarity exerts an adverse effect on the reaction. Au3+ complexes react with the zwitterion form of isoleucine in a one-step two-electron transfer redox process. The reaction passes through intermediate formation of iminic cation, which hydrolyzes to produce 2-methyl butanal, identified by 1H NMR. The activation parameters ΔH≠ and ΔS≠ related to the rate-limiting step of the reaction are evaluated. The derived rate law is in excellent agreement with the experimental results. The kinetic and activation parameters of this investigation have been compared and analyzed with those of the oxidation of l-leucine by gold(III).

Mechanistic study of [RuCl3(H2O)2OH]− catalyzed oxidation of l-leucine by acidic N-bromophthalimide

Kinetic studies in homogenous Ru(III) catalyzed oxidation of l-leucine (Leu), by N-bromophthalimide (NBP) in the presence of perchloric acid have been made at 303 K using mercuric acetate as Br− ion scavenger. The reaction follows first-order kinetics with respect to [NBP]. In the lower concentration range of Leu and Ru(III) chloride, the reaction follows first-order kinetics but tends to zero at higher concentration. A positive effect of [Cl−] was observed in the oxidation of Leu. An increase in the rate of reaction with the decrease in dielectric constant of the medium was observed while negative effect was observed for [H+]. The rate of oxidation is unaffected by the change in [phthalimide (NHP)]. Rate of reaction decreased with increase in ionic strength of the medium. The main oxidation products of the reactions were identified as aldehyde, ammonia and CO2 for the oxidation of Leu. From the effect of temperature (298–318 K) on the reaction rate, various activation parameters have been calculated and on the basis of these parameters, a suitable explanation for the reaction mechanism has been given.

Kinetics of Oxidation of L-Leucine by Mono- and Bimetallic Gold and Silver Nanoparticles in Hydrogen Peroxide Solution

The catalytic activity of surfactant stabilized mono- and bimetallic Au and Ag nanoparticles for the oxidation of an amino acid, L-leucine, was studied using hydrogen peroxide as the oxidant. The Au and Ag nanoparticle catalysts exhibited very good catalytic activity and the kinetics of the reaction were found to be pseudo-first order with respect to the amino acid. The effects of several factors, such as oxidant concentration, ionic strength, pH, and catalyst concentration on the reaction, were also investigated. In particular, optimal oxidant and catalyst concentrations were determined. Very high concentrations of the metal nano-catalysts or the oxidant led to a dramatic increase in reaction rate. Moreover, bimetallic Au-Ag catalysts provided higher selectivity than pure Au or Ag. The catalytic activity of mono- and bimetallic nanoparticles was studied for the oxidation of L-leucine using aqueous hydrogen peroxide. The reaction kinetics was studied in terms of the effect of oxidant concentration, catalyst type and concentration, ionic strength, and pH.

Kinetics and mechanism of oxidation of L-leucine by alkaline diperiodatocuprate(III) — A free radical intervention, deamination and decarboxylation

The kinetics of oxidation of L-leucine by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm − 3 was studied spectrophotometrically. The reaction between L-leucine and DPC in alkaline medium exhibits 1:4 stoichiometry (L-leucine: DPC). The reaction is of first order in [DPC] and has less than unit order in both [L-leucine] and [alkali]. However, the order in [L-leucine] and [alkali] changes from first order to zero order as their concentration increase. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreased the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate (III) – L-leucine complex, which decomposed slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test and GC-MS. The reaction constants involved in the different steps of the mechanism were calculated. The title reaction was studied spectrophotometrically and a suitable mechanism was proposed. The thermodynamic quantities of different steps of the mechanism were evaluated. The active species of DPC was found to be [Cu(H2IO6)(H2O)2].

Effect of CTAB Micelle on the Oxidation of L-Leucine by N-Bromophthalimide: a Kinetic Study

Abstract The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) on the oxidation of L-leucine by N-bromophthalimide (NBP) has been studied at 308 K. The reaction exhibits first order dependence on NBP and L-leucine and negative and fractional order dependence on HClO4. The effects of KCl, KBr, phthalimide and mercuric acetate have also been studied and summarized. The rate of reaction increased with an increase in dielectric constant of the medium. CTAB strongly catalyzes the reaction and typical k obs and CTAB profile was observed, i.e., with a progressive increase in CTAB, the reaction rate increased and after achieving a peak k obs decreased at higher concentrations of CTAB. The results are treated quantitatively in terms of “Piszkiewicz” and “Raghvan and Srinivasan's” models. The various activation parameters in presence and absence of CTAB have been also evaluated. A suitable mechanism consistent with the experimental findings has been proposed. The rate constant in micellar phase k M, cooperativity index (n), binding constant (K 1 and K 2) have been computed.

Antigenic, microbicidal and antiparasitic properties of an l-amino acid oxidase isolated from Bothrops jararaca snake venom

Venoms from the bee Apis mellifera, the caterpillar Lonomia achelous, the spiders Lycosa sp. and Phoneutria nigriventer, the scorpions Tityus bahiensis and Tityus serrulatus, and the snakes Bothrops alternatus, Bothrops jararaca, Bothrops jararacussu, Bothrops moojeni, Bothrops neuwiedi, Crotalus durissus terrificus, and Lachesis muta were assayed (800 μg/mL) for activity against Staphylococcus aureus. Venoms from B. jararaca and B. jararacussu showed the highest S. aureus growth inhibition and also against other Gram-positive and Gram-negative bacteria. To characterize the microbicidal component(s) produced by B. jararaca, venom was fractionated through gel exclusion chromatography. The high molecular weight, anti- S. aureus P1 fraction was further resolved by anion exchange chromatography through Mono Q columns using a 0–0.5 M NaCl gradient. Bactericidal Mono Q fractions P5 and P6 showed significant LAAO activity using l-leucine as substrate. These fractions were pooled and subjected to Heparin affinity chromatography, which rendered a single LAAO activity peak. The anti- S. aureus activity was abolished by catalase, suggesting that the effect is dependent on H 2O 2 production. SDS-PAGE of isolated LAAO indicated the presence of three isoforms since deglycosylation with a recombinant N-glycanase rendered a single 38.2 kDa component. B. jararaca LAAO specific activity was 142.7 U/mg, based on the oxidation of l-leucine. The correlation between in vivo neutralization of lethal toxicity (ED 50) and levels of horse therapeutic antibodies anti-LAAO measured by ELISA was investigated to predict the potency of Brazilian antibothropic antivenoms. Six horses were hyperimmunized with Bothrops venoms (50% from B. jararaca and 12.5% each from B. alternatus, B. jararacussu, B. neuwiedii and B. moojeni). To set up an indirect ELISA, B. jararaca LAAO and crude venom were used as antigens. Correlation coefficients ( r) between ED 50 and ELISA antibody titers against B. jararaca venom and LAAO were 0.846 ( p < 0.001) and 0.747 ( p < 0.001), respectively. The hemolytic and leishmanicidal (anti- Leishmania amazonensis) activity of LAAO was also determined.

Ruthenium(III) catalysed oxidation of l-leucine by a new oxidant, diperiodatoargentate(III) in aqueous alkaline medium

The kinetics of Ru(III) catalysed oxidation of l-leucine by diperiodatoargentate(III) (DPA) in alkaline medium at 298 K and a constant ionic strength of 0.60 mol dm −3 was studied spectrophotometrically. The oxidation products are pentanoic acid and Ag(I). The stoichiometry is [ l-leucine]:[DPA] = 1:2. The reaction is of first order in Ru(III) and [DPA] and has less than unit order in both [ l-leu] and [alkali]. The oxidation reaction in alkaline medium has been shown to proceed via a Ru(III)– l-leucine complex, which further reacts with one molecule of monoperiodatoargentate(III) (MPA) in a rate determining step followed by other fast steps to give the products. The main products were identified by spot test and spectral studies. The reaction constants involved in the different steps of the mechanism are calculated. The catalytic constant ( K c) was also calculated for the Ru(III) catalysed reaction at different temperatures. From the plots of log K c versus 1/ T, values of activation parameters with respect to the catalyst have been evaluated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The active species of catalyst and oxidant have been identified.

Oxidation of l-Leucine by Alkaline Diperiodatoargentate(III) Deamination and Decarboxylation: A Kinetic and Mechanistic Study

The oxidation of l-Leucine by alkaline diperiodatoargentate(III) (DPA) at 298 K and a constant ionic strength of 1.0 mol dm-3 was studied spectrophotometrically. The oxidation products are pentanoic acid and Ag (I). The stoichiometry is [l-Leucine]:[DPA] = 1:2. The reaction is of first order in [DPA] and has less than unit order in both [l-Leucine] and [alkali] and a retarding effect in [IO4-]. The oxidation reaction in alkaline medium has been shown to proceed via a l-Leucine−DPA complex, which further reacts with one molecule of DPA in a rate-determining step followed by other fast steps to give the products. The main products were identified by spot test and IR. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined. The probable active species of oxidation have been identified.

Comparative study of the chromium(III) catalysed oxidation of l-leucine and l-isoleucine by alkaline permanganate: A kinetic and mechanistic approach

The kinetics of the chromium(III) catalysed oxidation of l-leucine and l-isoleucine by alkaline permanganate were studied and compared, spectrophotometrically. The reaction is first order with respect to (oxidant) and (catalyst) with an apparently less than unit order in (substrate) and zero order with respect to (alkali). The results suggest the formation of a complex between the amino acid and the hydroxylated species of chromium(III). The complex reacts further with the permanganate in a rate-determining step, resulting in the formation of a free radical, which again reacts with the permanganate in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were obtained. There is a good agreement between observed and calculated rate constants under different experimental conditions. The activation parameters with respect to slow step of the mechanism for both the amino acids were calculated and discussed. Of the two amino acids, leucine is oxidised at a faster rate than the isoleucine.

Kinetics and Mechanism of Oxidation of L-Leucine by Alkaline Diperiodatonickelate(IV) ? A Free Radical Intervention, Deamination, and Decarboxylation

Kinetics and Mechanism of Oxidation of L-Leucine by Alkaline Diperiodatonickelate(IV) ? A Free Radical Intervention, Deamination, and Decarboxylation

A comparative study of ruthenium(III) catalysed oxidation of L-leucine and L-isoleucine by alkaline permanganate. A kinetic and mechanistic approach

The kinetics of the Ru I I I -catalysed oxidation of L-leucine and L-isoleucine by alkaline permanganate were studied and compared, spectrophotometrically using a rapid kinetic accessory. The reaction is first order with respect to [oxidant] and [catalyst] with an apparently less than unit order in [substrate] and [alkali] respectively. The results suggest the formation of a complex between the amino acid and the hydroxylated species of ruthenium(III). The complex reacts further with the alkaline permanganate species in a rate-determining step, resulting in the formation of a free radical, which again reacts with the alkaline permanganate species in a subsequent fast step to yield the products. The reaction constants involved in the mechanism were calculated. There is a good agreement between observed and calculated rate constants under different experimental conditions. The activation parameters with respect to the slow step of the mechanism for both the amino acids were calculated and discussed. Of the two amino acids, leucine is oxidised at a faster rate than isoleucine.

Amperometric flow-injection analysis of creatinine based on immobilized creatinine deiminase, leucine dehydrogenase and L-amino acid oxidase

Leucine dehydrogenase/ l-amino acid oxidase was proposed as an enzymatic conversion system for ammonia and its application to amperometric assay of creatinine was investigated. Ammonia formed by creatinine deiminase catalyzed hydrolysis of creatinine was converted to l-leucine by leucine dehydrogenase, and the oxidation of l-leucine by l-amino acid oxidase was detected with an oxygen electrode. Two approaches were proposed to overcome the problem of endogenous ammonia and l-amino acids. The first was using glutamate dehydrogenase prereactor to remove endogenous ammonia; endogenous l-amino acids were corrected by a separate run. In the second approach, endogenous ammonia and l-amino acids were simultaneously compensated with a two-channel system. It resulted in double peak recording that the flow was split and rejoined between the two ends of creatinine deiminase reactor and a delay coil and a reference column were properly set at one of the two-channels. One gave the sum response of all responsible compounds, the other that of endogenous interferences except creatinine. Both approaches were applied to creatinine assay in urine and the results showed a good agreement with those obtained from the Jaffe method.

Kinetic study of permanganate oxidation of L-leucine in neutral aqueous solution

The permanganate oxidation of L-leucine in aqueous phosphate buffers over the pH range 6.1 – 7.6 is autocatalyzed by the manganese reduction product, a soluble form of colloidal manganese dioxide. The kinetic data for both the non-catalytic and autocatalytic reaction pathways have been obtained, and mechanism in agreement with them proposed. The non-catalytic pathway takes place by reaction between either the anionic or the zwitterionic form of the amino acid and permanganate ion, whereas the autocatalytic pathway is realized by the permanganate oxidation of the amino acid previously adsorbed on the colloid surface.

The coupling of metabolic to secretory events in pancreatic islets. The possible role of glutathione reductase

The participation of glutathione reductase in the process of nutrient-stimulated insulin release was investigated in rat pancreatic islets exposed to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). BCNU caused a time-and dose-related, irreversible inhibition of glutathione reductase activity. This coincided with a fall in both GSH/GSSG ratio and the thiol content of the islets. Pretreatment of the islets with BCNU inhibited the oxidation of glucose and its stimulant action upon both 45Ca net uptake and insulin release. Although BCNU (up to 0.5 mM) failed to affect the oxidation of l-leucine and l-glutamine, it also caused a dose-related inhibition of insulin release evoked by the combination of these two amino acids. The latter inhibition was apparently not fully accounted for by the modest to negligible effects of BCNU upon 45Ca uptake, 45Ca efflux, 86Rb efflux and cyclic AMP production. Since BCNU failed to inhibit insulin release evoked by the association of Ba 2+ and theophylline, these results support the view that glutathione reductase participates in the coupling of metabolic to secretory events in the process of nutrient-stimulated insulin release. However, the precise modality of such a participation, for example the control of intracellular Ca 2+ distribution, remains to be elucidated.

The stimulus-secretion coupling of amino acid-induced insulin release metabolic interaction L-asparagine and L-leucine in pancreatic islets

1. Because L-asparagine augments insulin release evoked by L-leucine, the metabolism of these two amino acids was investigated in rat pancreatic islets. 2. L-Leucine inhibited the uptake and deamidation of L-asparagine, but failed to exert any obvious primary effect upon the further catabolism of aspartate derived from exogenous asparagine. 3. L-Asparagine augmented the oxidation of L-leucine, and effect possibly attributable to activaion of 2-ketoisocaproate dehydrogenase. 4. The association of L-asparagine and L-leucine exerted a sparing action on the utilization of endogenous amino acids, so that the integrated rate of nutrients oxidation was virtually identical in the sole presence of L-leucine and simultaneous presence of L-asparagine and L-leucine, respectively. 5. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine is attributable to an increased generation rate of cytosolic NADPH rather than any increase in nutrients oxidation.

Properties of crystalline leucine dehydrogenase from Bacillus sphaericus

The distribution of bacterial leucine dehydrogenase (L-leucine:NAD+ oxidoreductase, deaminating, EC 1.4.1.9) was investigated, and Bacillus sphaericus (IFO 3525) was found to have the highest activity of the enzyme. Leucine dehydrogenase, which was purified to homogeneity and crystallized from B. sphaericus, has a molecular weight of about 245,000 and consists of six identical subunits (Mr = 41,000). The enzyme catalyzes the oxidative deamination of L-leucine, L-valine, L-isoleucine, L-norvaline, L-alpha-aminobutyrate, and L-norleucine, and the reductive amination of their keto analogues. The enzyme requires NAD+ as a cofactor, which cannot be replaced by NADP+. D-Enantiomers of the substrate amino acids inhibit competitively the oxidation of L-leucine. The enzyme activity is significantly reduced by both sulfhydryl reagents and pyridoxal 5'-phosphate. Purine and pyrimidine bases, nucleosides and nucleotides have no effect on the enzyme activity. Initial velocity and product inhibition studies show that the reductive amination proceeds through a sequential ordered ternary-binary mechanism. NADH binds first to the enzyme followed by alpha-ketoisocaproate and ammonia, and the products are released in the order of L-leucine and NAD+. The Michaelis constants are as follows: L-leucine (1 mM), NAD+ (0.39 mM), NADH (35 micrometer), alpha-ketoisocaproate (0.31 mM), and ammonia (0.2 M). The pro-S hydrogen at C-4 of the dihydronicotinamide ring of NADH is exclusively transferred to the substrate; the enzyme is B-stereospecific.

Tyrosine Aminotransferase in AKR/J Albino and C57BL/6J Black Mouse Skin

L-Tyrosine aminotransferase is present in a high speed supernatant fraction of skin homogenate of AKR/J albino and C57BL/6J black mice. The conversion of tyrosine to p-hydroxyphenylpyruvate was shown to be catalyzed by an aminotransferase by the following observations: the reaction was partially dependent on the presence of low concentrations of alpha-ketoglutarate; catalase was ineffective in increasing the yield of p-hydroxyphenylpyruvate; there was potent inhibition by typical inhibitors of pyridoxal phosphate enzymes and of rat liver tyrosine aminotransferase; there was no inhibition by inhibitors of L-amino acid oxidase; and there was no oxidation of L-leucine, the best substrate for rat kidney L-amino acid oxidase. The aminotransferase was stimulated by mercaptoethanol and was inhibited by high concentrations of alpha-ketoglutarate. The apparent Km for tyrosine was 5 X 10(-3) M and the molecular weight, determined by sucrose density gradient centrifugation, was 150-200,000. Dopa was also transaminated by the crude enzyme. No tyrosine aminotransferase could be detected in extracts of hamster melanoma.

Crystalline Mammalian l-Amino Acid Oxidase from Rat Kidney Mitochondria

Abstract l-Amino acid oxidase has been crystallized from extracts of rat kidney mitochondria. Purification involved sonic extraction, ammonium sulfate fractionation, chromatography on diethylaminoethyl cellulose, and gel filtration through Sephadex G-200. The enzyme revealed a single protein band on starch gel electrophoresis and exhibited a single homogeneous peak (s20, w0 = 10.5 S) in an ultracentrifuge. The enzyme is a flavoprotein in which the prosthetic group appears to be flavin mononucleotide. On the basis of the flavin mononucleotide content of the enzyme (0.92%) and its molecular weight (88,900 ± 1,100), it has been concluded that the enzyme contains 2 moles of flavin mononucleotide per mole. The enzyme catalyzes the oxidation of many α-aminomonocarboxylic and α-hydroxy acids (l configuration) but has no action on optically inactive acids such as glycine and α-hydroxyisobutyric acid. The turnover numbers for the oxidation of l-leucine and of l-lactic acid were 6.3 and 26 moles per min per mole of flavin mononucleotide conjugated with enzyme, respectively.