Tryptophan Complex Research Articles

Tryptophan As a New Member of RNA-Induced Silencing Complexes Prevents Colon Cancer Liver Metastasis.

Essential amino acids (EAA) and microRNAs (miRs) control biological activity of a cell. Whether EAA regulates the activity of miR has never been demonstrated. Here, as proof-of-concept, a tryptophan (Trp, an EAA) complex containing Argonaute 2 (Ago2) and miRs including miR-193a (Trp/Ago2/miR-193a) is identified. Trp binds miR-193a-3p and interacts with Ago2. Trp/Ago2/miR-193a increases miR-193a-3p activity via enhancing Argonaute 2 (Ago2) RNase activity. Other miRs including miR-103 and miR-107 in the Trp complex enhance miR-193a activity by targeting the same genes. Mechanistically, the Trp/Ago2/miR-193a complex interacts with Trp-binding pockets of the PIWI domain of Ago2 to enhance Ago2 mediated miR activity. This newly formed Ago2/Trp/miR-193a-3p complex is more efficient than miR-193a-3p alone in inhibiting the expression of targeted genes and inhibiting colon cancer liver metastasis. The findings show that Trp regulates miR activity through communication with the RNA-induced silencing complexes (RISC), which provides the basis for tryptophan based miR therapy.

Development of anti-corrosive coating on AZ31 Mg alloy modified by MOF/LDH/PEO hybrids

The self-assembly of hybrid inorganic-organic materials on stationary platforms plays a critical role in improving their structural stability and wide usability. In this work, a novel two-step hydrothermal approach is proposed for synthesizing stable and advanced hybrid coatings on metal-oxide platforms through the surface modification of layered double hydroxide (LDH) films using novel metal-organic frameworks (MOFs). Initially, Mg-Al LDH nanocontainers, grown on a magnesium oxide layer produced through plasma electrolytic oxidation (PEO) of AZ31 Mg alloy substrate, were intercalated with cobalt via an oxidation route, providing the metallic coordination center for the MOF formation. In the subsequent step, a pioneering technique is introduced, utilizing tryptophan as the organic linker for the first time at a pH of 10. The self-assembly of cobalt- tryptophan complex, driven by the strong bonding between electrophilic sites of monomers and nucleophilic sites, facilitated the formation of a MOF network having a cloud-like structure on the surface of MgAl LDH's film. The resulting MOF-LDH encapsulation containers demonstrate exceptional electrochemical stability when exposed to a 3.5 wt.% NaCl solution, surpassing the performance of PEO and pure LDH coatings. This enhanced stability is attributed to the development of a dense top layer and a stable composition within the self-assembled MOF, effectively sealing flaws and preventing the infiltration of corrosive ions into the underlying metallic substrate. The formation mechanism of MOFs on LDH galleries is investigated using density functional theory calculations.

Acidithiobacillus ferrooxidans mediates morphology evolution of schwertmannite in the presence of Fe2+

Schwertmannite (Sch) possessing a typical “hedgehog” morphology is ubiquitously found in acid mine drainage (AMD) through biological oxidation of Fe2+ by Acidithiobacillus ferrooxidans (Acidithiobacillus ferrooxidans). However, little information is available on the effect of A. ferrooxidans on the morphology evolution of Sch during its formation. In this study, it was found that Fe2+ and A. ferrooxidans (with the presence of Fe2+) could promote the “hedgehog” structure formation of Sch in acid aerobic environment, respectively. Aerobic systems led to the increase in needle-like goethite on the surface of ellipsoidal aggregates with comparison to anaerobic systems. Hydroxyl radical (OH) produced only in the aerobic systems facilitated the formation of Fe3+. Meanwhile, A. ferrooxidans, containing mainly tryptophan, could significantly change the interfacial potential and favor the electron transfer from Fe2+ to Sch. Moreover, it also could coordinate with Fe (Fe2+, Fe3+). Thus, a possible mechanism for developing a typical “hedgehog” morphology of biogenic Sch was that Fe3+ from OH oxidization of Fe2+ and/or released from Sch would chelate with tryptophan to form Fe3+-tryptophan complex, and further induce the formation of needle-like goethite. However, during the crystal growth of goethite, tryptophan would be released to solution. These findings have important implications for comprehensively understanding the role of microorganism on mineral formation in AMD environment.

Влияние наноалмазов на усиление флуоресценции продуктов реакции фототрансформации триптофана в присутствии галогенуглеводородов

The role of nanodiamonds in the reaction of photochemical transformation of tryptophan in the presence of halogen hydrocarbons has been studied. The photochemical transformation of free tryptophan in a suspension with diamond nanoparticles and in a hybrid complex with them when exposed to UV radiation in the presence of chloroform is investigated. Data from stationary and time-resolved spectroscopic studies show the presence of non-radiative transfer of electron excitation energy between tryptophan molecules and its photodestruction products for the case of a covalent complex with a nanodiamond. It is shown that in the presence of energy transfer, an increase in the intensity of integral fluorescence occurs in the range of ~ 450 nm. Thus, a covalent tryptophan complex with a nanodiamond can serve as a fluorescent marker for the presence of chloroform in solution.

Effect of nanodiamonds on fluorescence enhancement of tryptophan phototransformation reaction products in the presence of halocarbons

The role of nanodiamonds in the reaction of photochemical transformation of tryptophan in the presence of halogen hydrocarbons has been studied. The photochemical transformation of free tryptophan in a suspension with diamond nanoparticles and in a hybrid complex with them when exposed to UV radiation in the presence of chloroform is investigated. Data from stationary and time-resolved spectroscopic studies show the presence of non-radiative transfer of electron excitation energy between tryptophan molecules and its photodestruction products for the case of a covalent complex with a nanodiamond. It is shown that in the presence of energy transfer, an increase in the intensity of integral fluorescence occurs in the range of ~ 450 nm. Thus, a covalent tryptophan complex with a nanodiamond can serve as a fluorescent marker for the presence of chloroform in solution. Keywords: nanoscale diamonds, hybrid complexes, tryptophan phototransformation, spectral-luminescent properties, fluorescence decay kinetics, chloroform.

Interaction of dirhenium(III) tryptophan complex compound with DNA and protein

We report about the interactions of dirhenium(III) compound cis-[Re2(Trp)2Cl4(CH3CN)2]Cl2 (I) with bovine serum protein (BSA) and guanine (G4) quadruplexes DNA by UV-Vis titration. Addition of I to BSA led to the interaction between these compounds with binding constant 5.6103 M–1 and hyperchromism (20.9%) of the main protein absorption band (280 nm). These results support our assumption about formation of the additional conjugated systems during the process of interaction with BSA. Stabilization of the quadruple bonded rhenium(III) complex compound was shown in the presence of BSA (the rate of destruction was reduced), that may be explained by interaction between amino acid residues of BSA and quadruple bond of dirhenium(III) complex compound. In addition, we have obtained data about strong hyperchromism (up to 100%) and significant shift of the maximum of absorption (blue shift) towards UV (2–9 nm) and visible (22 nm) regions in the spectra of mixtures G4s and I, that, in our opinion, correlated with a conformational change in DNA and with formation of additional conjugated systems around quadruple bond of I. In a whole, our work confirms the strong binding activity of a cluster dirhenium(III) compound towards G4 quadruplexes, that exceed the binding activity to proteins and witness to preferential interactions of I with G4 DNA in a living cell. These results may be used in DNA "silencing technology" and "antisense therapy".

Improving the short-term efficiency of rock phosphate-based fertilizers in pastures by using edaphic biostimulants

The use of reactive rock phosphate (RP) in acidic soils as a phosphate (P) source for pastures and crops presents attractive economic advantages with respect to soluble phosphate. However, some studies have demonstrated that the short-term (1-year) efficiency of RP, compared with that of water-soluble P, is relatively poor. This fact penalizes not only the yield and quality of the earlier harvests, but even the whole final yield when the crop is affected by some abiotic or biotic stress at the beginning of the cycle. In the present study, we investigated the ability of new edaphic biostimulants to increase the short-term efficiency of RP-based fertilizer as a P source for pastures cultivated in acid soils. To this end, we have granulated rock phosphate with two edaphic biostimulants: tryptophan and a heteromolecular organic complex formed by humic acid and tryptophan through iron bridges, and compared their short-term P fertilizer efficacy with that of single superphosphate and rock phosphate. Soil incubation studies showed that the heteromolecular complex humic acid–tryptophan and Tryptophan were able to increase soil CO2 production compared with native soil, rock phosphate, and superphosphate. Likewise, the presence of humic acid–tryptophan complex and Trp significantly increases plant-available phosphate compared with rock phosphate, up to levels similar to those of superphosphate. Plant (ray grass)–soil–pot studies showed that rock phosphate/(humic acid–tryptophan) formulation yielded values for both ray grass dry matter production and shoot P concentration, clearly higher than those of rock phosphate and rock phosphate/tryptophan. In addition, the results associated with rock phosphate/(humic acid–tryptophan) were similar to those for superphosphate, after 3 months of cultivation. Taken together, these results showed the suitability of the use of specific humic acid-based edaphic biostimulants to improve the short-term effect of rock phosphate fertilizers as a phosphate source for pastures cultivated in acid soils.

Accurate Nitric Oxide Measurements from Donors in Cell Media: Identification of Scavenging Agents

Nitric oxide (NO) is an essential messenger in human physiology, mediating cellular processes ranging from proliferation to apoptosis. The effects of NO are concentration dependent, and control over the instantaneous amount of NO available to cells is essential for determining the therapeutic NO dosages for various applications. As such, the development of NO therapeutic materials relies on accurate quantitative NO measurements that provide both total NO release from the NO donor as well as instantaneous NO concentrations. On the basis of the complexity of the cell media environment, inaccurate NO reporting often occurs for in vitro studies. These inaccuracies result from using inert media such as phosphate buffer saline (PBS), failing to account for the reactivity of media components. In this work, we describe a method for directly quantifying the instantaneous and total amounts of NO from commonly used NO donors in commercially available cell media routinely used for endothelial and neural cell lines. A riboflavin-tryptophan complex found in the media was identified as the major scavenger of NO in the cell media and likely reacts with NO via a radical-radical reaction. This finding significantly impacts the amount of available NO. The scavenging effects are concentration dependent on the riboflavin-tryptophan complex and the NO release rate from the NO donor. The results of this study provide insights on the exogenous amounts of NO that are present in cell media and may provide an explanation for differences in NO dosages between buffer experiments and in vitro and in vivo studies.

Enantiomeric resolution of tryptophan via stereoselective binding in an ion-exchange membrane partitioned free flow isoelectric focusing system

The optical resolution efficiency of a membrane system that integrates stereoselective affinity dialysis and ion-exchange membrane partitioned free flow isoelectric focusing (FFIEF) is shown to be superior to normal affinity dialysis (AD) and affinity ultrafiltration (AUF) membrane processes under similar experimental conditions, i.e. by using the same sulfonated polyetherketone (SPEK) membranes and identical human serum albumin (HSA) to tryptophan ratio of 0.75. The chiral separation is achieved by isolating the unbound tryptophan, which contains D-tryptophan in excess, and the protein–tryptophan complex into the permeation and feed chambers, respectively, by controlling their migration under an external electric field. The separation factor is increased with increasing protein concentration while the permeation flux can be enhanced by increasing the operating current. The rationale for using HSA instead of BSA as the chiral selector, and the use of four-chamber system rather than two are also discussed.

Single Turnover Kinetics of Tryptophan Hydroxylase: Evidence for a New Intermediate in the Reaction of the Aromatic Amino Acid Hydroxylases

Tryptophan hydroxylase (TrpH) uses a non-heme mononuclear iron center to catalyze the tetrahydropterin-dependent hydroxylation of tryptophan to 5-hydroxytryptophan. The reactions of the TrpH.Fe(II), TrpH.Fe(II).tryptophan, TrpH.Fe(II).6MePH(4).tryptophan, and TrpH.Fe(II).6MePH(4).phenylalanine complexes with O(2) were monitored by stopped-flow absorbance spectroscopy and rapid quench methods. The second-order rate constant for the oxidation of TrpH.Fe(II) has a value of 104 M(-1) s(-1) irrespective of the presence of tryptophan. Stopped-flow absorbance analyses of the reaction of the TrpH.Fe(II).6MePH(4).tryptophan complex with oxygen are consistent with the initial step being reversible binding of oxygen, followed by the formation with a rate constant of 65 s(-1) of an intermediate I that has maximal absorbance at 420 nm. The rate constant for decay of I, 4.4 s(-1), matches that for formation of the 4a-hydroxypterin product monitored at 248 nm. Chemical-quench analyses show that 5-hydroxytryptophan forms with a rate constant of 1.3 s(-1) and that overall turnover is limited by a subsequent slow step, presumably product release, with a rate constant of 0.2 s(-1). All of the data with tryptophan as substrate can be described by a five-step mechanism. In contrast, with phenylalanine as substrate, the reaction can be described by three steps: a second-order reaction with oxygen to form I, decay of I as tyrosine forms, and slow product release.

Mechanism of Inhibition of Novel Tryptophan Hydroxylase Inhibitors Revealed by Co-crystal Structures and Kinetic Analysis

Trytophan Hydroxylase Type I (TPH1), most abundantly expressed in the gastrointestinal tract, initiates the synthesis of serotonin by catalyzing hydroxylation of tryptophan in the presence of biopterin and oxygen. We have previously described three series of novel, periphery-specific TPH1 inhibitors that selectively deplete serotonin in the gastrointestinal tract. We have now determined co-crystal structures of TPH1 with three of these inhibitors at high resolution. Analysis of the structural data showed that each of the three inhibitors fills the tryptophan binding pocket of TPH1 without reaching into the binding site of the cofactor pterin, and induces major conformational changes of the enzyme. The enzyme-inhibitor complexes assume a compact conformation that is similar to the one in tryptophan complex. Kinetic analysis showed that all three inhibitors are competitive versus the substrate tryptophan, consistent with the structural data that the compounds occupy the tryptophan binding site. On the other hand, all three inhibitors appear to be uncompetitive versus the cofactor 6-methyltetrahydropterin, which is not only consistent with the structural data but also indicate that the hydroxylation reaction follows an ordered binding mechanism in which a productive complex is formed only if tryptophan binds only after pterin, similar to the kinetic mechanisms of tyrosine and phenylalanine hydroxylase.

An efficient use of the WATERGATE W5 sequence for observing a ligand binding with a protein receptor

An efficient pulse sequence for observing a ligand binding with a receptor has been developed by incorporating the WATERGATE W5 sequence. In the conventional water ligand observed via gradient spectroscopy (WaterLOGSY) techniques, the water resonance is selectively excited using, e.g. the double-pulsed field gradient spin-echo (DPFGSE) sequence at the initial portion of pulse sequence. In the current version, the modified WATERGATE W5 sequence is incorporated at the initial portion of the pulse sequence, and the resonance at the water frequency can be selectively reserved by the modified WATERGATE W5 sequence. The efficiency of ligand-observed NMR screening techniques has been demonstrated using the human serum albumin (HSA)-tryptophan complex.

Determination of curcumin by its quenching effect on the fluorescence of Eu 3+–tryptophan complex

Curcumin (C 21H 20O 6, CU) is a natural antioxidant, which is considered to be a very useful compound in health matters, and is employed in the treatment of cardiovascular and arthritic illnesses. It is found that the fluorescence intensity of Eu 3+–tryptophan (Trp) can be greatly quenched by curcumin in the buffer of pH 7.7. Under optimum conditions, the quenched intensity of fluorescence is in proportion to the concentration of curcumin in the range of 1.0 × 10 −8 to 1.2 × 10 −4 mol L −1. The detection limit (S/N = 3) is 9.0 × 10 −10 mol L −1. The synthetic and actual samples are satisfactorily determined. In addition, the interaction mechanism is also investigated.

Characterization of bovine serum albumin–tryptophan interaction by capillary isoelectric focusing with whole column imaging detection

Capillary isoelectric focusing (cIEF) with whole column imaging detection (WCID) was explored for the characterization of bovine serum albumin (BSA)–tryptophan interaction, to further understand protein–drug interactions. The BSA–tryptophan interaction was dynamically monitored by cIEF–WCID, to provide the cIEF profiles of the BSA–tryptophan interaction system at different focusing times. Our study demonstrated that the cIEF behavior of BSA can serve as a probe into the study of BSA–tryptophan interaction, through monitoring the change in its cIEF profile when the interaction occurred. The study illustrated that the BSA peak split due to the BSA–tryptophan interaction, and the peak of BSA–tryptophan complex was clearly identified in the cIEF electropherograms. By comparing the cIEF profiles of BSA/ l-tryptophan and BSA/ d-tryptophan, respectively, our study demonstrated that BSA interacted with the enantiomers of tryptophan with a chiral recognition. l-Tryptophan demonstrated a very strong interaction with BSA, while d-tryptophan exhibited a much weaker interaction with BSA. The effects of the BSA concentration, the tryptophan concentration, the focusing time and the incubation time on the BSA–tryptophan interaction were investigated. This study offers a novel approach for the study of protein–drug interactions.

Indirect fluorescence detection of amino sugars with the use of copper complexes of tryptophan and its analogues following high-performance liquid chromatographic separation

A simple, indirect fluorescence detection method has been developed for detecting specific mono-amino sugars ( d-glucosamine, d-galactosamine, d-mannosamine) following chromatographic separation. The eluting amino sugars release l-tryptophan ( l-Trp) from a copper–tryptophan complex which is introduced postcolumn. Analyte detection is based on measuring the increase in l-Trp fluorescence, which is quenched when complexed with copper. Two tryptophan analogues, 5-hydroxy- l-tryptophan (5-HTP) and dl-5-methoxytryptophan (5-MTP), were also evaluated as postcolumn reagents. 5-MTP was found to be a suitable alternative to l-Trp for the detection of these mono-amino sugars. Detection limits for d-glucosamine, d-galactosamine, and d-mannosamine are in the range of 0.15–0.30 nmol injected.

Ab initio study of hydrogen bonding interaction and photoinduced electron transfer between 4‐nitroquinoline‐1‐oxide and tryptophan

AbstractIn the present article, the electronic structure of 4‐nitroquinoline‐1‐oxide (4NQO) has been theoretically investigated at the level of HFSCF/6‐31G**. Conformation of monomeric 4NQO has been found to be the most stable when the nitro group twists from the quinoline plane by about 24°. The absorption spectra of the twisted 4NQO have been calculated by using complete active space self‐consistent field method. The hydrogen bonded complexes of 4NQO and tryptophan have been intensively studied. The absorption spectra of the most stable complex have been calculated to investigate the photoinduced electron transfer between 4NQO and tryptophan. The first and second excited singlet states are found to be charge‐separated. Population analysis shows that the low‐lying triplet states are charge‐separated as well, except for the lowest one that presents the characters of a locally excited state. A solvent effect on transition energies has been considered based on the Ooshika–Lippert–Martaga equation. Theoretical study shows that the optical excitation can lead to charge separation in the 4NQO–tryptophan complex. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Kinetics and Mechanism of the Reaction of Ninhydrin with Chromium(III)-tryptophan Complex in Absence and Presence of Surfactants

Kinetics and Mechanism of the Reaction of Ninhydrin with Chromium(III)-tryptophan Complex in Absence and Presence of Surfactants

Kinetics and Mechanism of the Reaction of Ninhydrin with Chromium(III)-tryptophan Complex in Absence and Presence of Surfactants

The kinetics of the title reaction have been investigated in both aqueous and micellar cetyltrimethylammonium bromide(CTAB) solutions. Rate data indicate that the reaction follows the template mechanism in both the media. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is ca. 4 -fold. The following parameters have been calculated at pH 5.0: for aqueous, kobs = 5.6 χ 10-5 s-1, ΔH* = 61 k J mol-1, ΔS* = -122 J K-1mol-1 ; for CTAB , kΨ = 24.7 χ 10-5 s-1 , ΔH* = 35 k J mol-1, ΔS* = -200 J K-1 mol-1, which reveal CTAB behaving as a catalyst. To explain the dependence of the reaction rate on [CTAB], pseudo-phase model proposed by Menger and Portnoy and modified by Bunton and Rodenas was used. The catalytic role of CTAB can be related to the extent of incorporation or association of the chromium(III)-tryptophan and ninhydrin into the micelles. Various factors which affect km, Ks KN and are discussed taking into account the micellar surface solvent properties.

Kinetics and Mechanism of the Reaction of Copper(II)-tryptophan Complex with Ninhydrin in Aqueous and Micellar Media

Kinetics of the title reaction has been investigated spectrophotometrically in aqueous solution as well as in the presence of cetyltrimethylammonium bromide (CTAB) cationic micelles. The reaction rate is first- and fractional-order with respect to [substrate] and [ninhydrin], respectively, both in the absence and presence of cationic micelles. Whereas SDS addition shows formation of a different product, the reaction of copper(II)-tryptophan complex with ninhydrin is catalyzed by CTAB: the maximum rate enhancement being ca . 5-fold. The data are interpreted in terms of the pseudo-phase model (assuming the association/incorporation of both the reactants at the micellar surface). The binding constants of copper(II)-tryptophan ( K S ) and ninhydrin ( K N ) with CTAB micelles have been calculated. The presence of inorganic salts (NaCl, NaBr, NaNO 3 and Na 2 SO 4 ) leads to a decrease in the rate followed by an increase and it is found that tightly bound/incorporated anions are most effective.

Electrochemical study of the interaction of nicotinamide with tryptophan in the presence and absence of nickel(II)

The interaction of nicotinamide with tryptophan in the presence and absence of nickel(II) in 0.1 M ammonium tartrate (pH 8.94) has been examined by voltammetric techniques. Tryptophan gave a catalytic hydrogen peak at −1.12 V versus an Ag ∣ AgCl ∣ saturated KCl reference electrode while nicotinamide formed two peaks at −1.42 and −1.57 V, respectively. In the absence of nickel(II), when the tryptophan concentration was increased, the peak of nicotinamide at −1.42 V increased gradually while its peak at −1.57 V decreased. It can be concluded that tryptophan plays an important role in the reduction mechanism of nicotinamide at the mercury electrode surface. Voltammetric results show that the nickel(II)–tryptophan and nickel(II)–nicotinamide complexes on the mercury electrode surface reduce at −0.44 and −0.94 V, respectively. These complexes are reduced at a more positive potential than that of the Ni(II)tartrate (−1.18 V). From electronic spectral data of the complexes, their stoichiometries of 1:1 (metal/ligand) in aqueous medium are determined. The interactions between tryptophan and nicotinamide were also studied in the presence of nickel(II). Excess nickel(II) causes changes in the voltammetric reduction peaks of nicotinamide and tryptophan and the formation of binary complexes. The nickel(II)–tryptophan (log β=2.3) complex is more predominant than that of nickel(II)–nicotinamide (log β=2.2) complex. This probably results from the binding sites and the size of the catalyst. Further, when nicotinamide was added to a solution containing the nickel(II)–tryptophan complex, or tryptophan to the cell including the nickel(II)–nicotinamide complex, the formation of a mixed-ligand complex was not seen.