scholarly journals Complexation of Calix[4]arene bis-Hydroxymethylenediphosphonic Acid with Amino acids. Binding Constants Determination by RP HPLC Method

2015 ◽  
Vol 3 (2) ◽  
pp. 93-100 ◽  
Author(s):  
Vitaly Kalchenko ◽  
Olga Kalchenko ◽  
Sergiy Cherenok
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Electrostatic Interactions ◽  
Water Solution ◽  
Binding Constants ◽  
Hplc Method ◽  
Log P ◽  
Rp Hplc ◽  
Solvophobic Interactions ◽  
Positively Charged

Host-Guest complexation of calixarene-bis-hydroxymethylenediphosphonic acid with 17 amino acids in water solution had been studied by the RP HPLC and molecular modelling methods. It had been shown the binding constants of the complexes are depended on the nature of the amino acid residue, log P and pKa of the acids. The complexation is mainly determined by the electrostatic interactions between the positively charged nitrogen atom of the amino acid and the negatively charged oxygen atom of phosphonic acid residue of the calixarene, the Host-Guest p-p, СН-p and solvophobic interactions.

scholarly journals Year-Long Validation Study and Reference Values for Urinary Amino Acids Using a Reversed-Phase HPLC Method

2001 ◽  
Vol 47 (3) ◽  
pp. 575-583 ◽  
Author(s):  
Rafael Venta
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Reference Values ◽  
Amino Acid Analysis ◽  
Reference Intervals ◽  
Reversed Phase ◽  
Hplc Method ◽  
Rp Hplc ◽  
Age Related

Abstract Background: Reversed-phase HPLC (RP-HPLC) has become an alternative to ion-exchange chromatography for amino acid analysis in biological fluids. However, validation studies for its urine application are limited, and the corresponding reference values have not been reported extensively. We studied the long-term performance of a commercial HPLC method for urine amino acid analysis and established specific age-related reference values for urine amino acid excretion. Methods: Method performance was continuously assessed by recovery and precision studies with urine samples and controls, respectively. Healthy individuals were prospectively analyzed throughout a 5-year period. Excretion of individual amino acids, expressed as mmol/mol of creatinine, was included in six age-related groups for random urine samples (0–1 month, 1–12 months, 1–3 years, 3–8 years, 8–16 years, and >16 years) and in two groups for 24-h urine collections (8–16 years and >16 years). Results: Over a 1-year period, CVs for retention times were <0.5% and 3.3% for within- and between-run imprecision, respectively. For amino acid concentrations, within-run CVs were 2.9–17% and between-run CVs were 7.1–46% for the same period. Amino acid recoveries were 78–122%. Reference intervals for 35 amino acids were calculated and compared with the concentrations observed in patients diagnosed with specific pathologies. A few statistically significant differences were found between the reference intervals derived using random and 24-h urine collections. Conclusions: Long-term reliability of the RP-HPLC method for urine amino acid analysis has been demonstrated. Representative age-related reference intervals for the RP-HPLC method in both random urine and 24-h urine collections have been established, and their feasibility for diagnosis of aminoaciduria has been shown. These intervals could serve as a guide for laboratories changing to HPLC methods.

scholarly journals SLC6A14, a Pivotal Actor on Cancer Stage: When Function Meets Structure

2019 ◽  
Vol 24 (9) ◽  
pp. 928-938 ◽  
Author(s):  
Luca Palazzolo ◽  
Chiara Paravicini ◽  
Tommaso Laurenzi ◽  
Sara Adobati ◽  
Simona Saporiti ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Amino Acids ◽  
Amino Acid ◽  
Molecular Dynamics Simulations ◽  
Electrostatic Interactions ◽  
Amino Acid Residues ◽  
Dibasic Amino Acid ◽  
Novel Target ◽  
Function Relationship ◽  
Dynamics Simulations

SLC6A14 (ATB0,+) is a sodium- and chloride-dependent neutral and dibasic amino acid transporter that regulates the distribution of amino acids across cell membranes. The transporter is overexpressed in many human cancers characterized by an increased demand for amino acids; as such, it was recently acknowledged as a novel target for cancer therapy. The knowledge on the molecular mechanism of SLC6A14 transport is still limited, but some elegant studies on related transporters report the involvement of the 12 transmembrane α-helices in the transport mechanism, and describe structural rearrangements mediated by electrostatic interactions with some pivotal gating residues. In the present work, we constructed a SLC6A14 model in outward-facing conformation via homology modeling and used molecular dynamics simulations to predict amino acid residues critical for substrate recognition and translocation. We docked the proteinogenic amino acids and other known substrates in the SLC6A14 binding site to study both gating regions and the exposed residues involved in transport. Interestingly, some of these residues correspond to those previously identified in other LeuT-fold transporters; however, we could also identify a novel relevant residue with such function. For the first time, by combined approaches of molecular docking and molecular dynamics simulations, we highlight the potential role of these residues in neutral amino acid transport. This novel information unravels new aspects of the human SLC6A14 structure–function relationship and may have important outcomes for cancer treatment through the design of novel inhibitors of SLC6A14-mediated transport.

X-ray studies on crystalline complexes involving amino acids and peptides. XL. Conformational variability, recurring and new features of aggregation, and effect of chirality in the malonic acid complexes of DL- and L-arginine

2002 ◽  
Vol 58 (6) ◽  
pp. 1051-1056 ◽  
Author(s):  
N. T. Saraswathi ◽  
M. Vijayan
Keyword(s):  
Amino Acids ◽  
Hydrogen Bonding ◽  
Amino Acid ◽  
Crystal Structures ◽  
Malonic Acid ◽  
Conformational Flexibility ◽  
X Ray ◽  
Conformational Variability ◽  
Aggregation Pattern ◽  
Positively Charged

The crystal structures of the complexes of malonic acid with DL- and L-arginine, which contain positively charged argininium ions and negatively charged semimalonate ions, further demonstrate the conformational flexibility of amino acids. A larger proportion of folded conformations than would be expected on the basis of steric consideration appears to occur in arginine, presumably because of the requirements of hydrogen bonding. The aggregation pattern in the DL-arginine complex bears varying degrees of resemblance to patterns observed in other similar structures. An antiparallel hydrogen-bonded dimeric arrangement of arginine, and to a lesser extent lysine, is a recurring motif. Similarities also exist among the structures in the interactions with this motif and its assembly into larger features of aggregation. However, the aggregation pattern observed in the L-arginine complex differs from any observed so far, which demonstrates that all the general patterns of amino-acid aggregation have not yet been elucidated. The two complexes represent cases where the reversal of the chirality of half the amino-acid molecules leads to a fundamentally different aggregation pattern.

RP-HPLC Determination of Tiger Nut and Orgeat Amino Acid Contents

2005 ◽  
Vol 11 (1) ◽  
pp. 33-40 ◽  
Author(s):  
L. Bosch ◽  
A. Alegría ◽  
R. Farré
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Profile ◽  
African Origin ◽  
Rp Hplc ◽  
Precision And Accuracy ◽  
Amino Acid Contents ◽  
Tiger Nuts ◽  
Abundant Amino Acid

The amino acid profile of 11 samples of tiger nuts ( Cyperus esculentusL.) grown in the area of “L'Horta Nord” in Valencia (Spain) and one sample of African origin were determined, along with the amino acid contents of 10 samples of natural orgeat from Valencia. Protein was hydrolysed by hydrochloric acid at 110 °C for 23 h, and amino acids were derivatised with AQC and determined by RP-HPLC with fluorescence detection. The chromatographic conditions were optimised. The analytical parameters (detection and quantification limits, precision and accuracy) showed the method to be sufficiently sensitive and reproducible for determining amino acids resistant to acid hydrolysis in tiger nuts and orgeat. Arginine was the most abundant amino acid in both tiger nuts and orgeat and the lowest contents corresponding to histidine and tyrosine. The essential amino acid contents of tiger nuts and orgeat protein were greater than those proposed in the protein standard for adults by the FAO/WHO, with the exception of histidine. No significant differences were found among the arginine, lysine and isoleucine amino acid contents in tiger nuts from Valencia, Alboraya and Alm‡ssera; nor were they found among amino acids in tiger nuts from Valencia and Alm‡ssera, with the exception of tyrosine.

RP-HPLC method with fluorescence detection for amino acids D /L ratio determination in fossil bones as a marker of DNA preservation

2010 ◽  
Vol 33 (16) ◽  
pp. 2411-2416 ◽  
Author(s):  
Piera Iuliani ◽  
Lucia Di Federico ◽  
Gabriella Fontecchio ◽  
Giuseppe Carlucci
Keyword(s):  
Amino Acids ◽  
Fluorescence Detection ◽  
Hplc Method ◽  
Dna Preservation ◽  
Rp Hplc ◽  
Fossil Bones ◽  
Ratio Determination

scholarly journals Modulating protein adsorption onto hydroxyapatite particles using different amino acid treatments

2011 ◽  
Vol 9 (70) ◽  
pp. 918-927 ◽  
Author(s):  
Wing-Hin Lee ◽  
Ching-Yee Loo ◽  
Kim Linh Van ◽  
Alexander V. Zavgorodniy ◽  
Ramin Rohanizadeh
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Protein Adsorption ◽  
Langmuir Model ◽  
The Body ◽  
Mineral Phase ◽  
Adsorption Ability ◽  
Adsorption Study ◽  
Lower Protein ◽  
Positively Charged

Hydroxyapatite (HA) is a material of choice for bone grafts owing to its chemical and structural similarities to the mineral phase of hard tissues. The combination of osteogenic proteins with HA materials that carry and deliver the proteins to the bone-defective areas will accelerate bone regeneration. The study investigated the treatment of HA particles with different amino acids such as serine (Ser), asparagine (Asn), aspartic acid (Asp) and arginine (Arg) to enhance the adsorption ability of HA carrier for delivering therapeutic proteins to the body. The crystallinity of HA reduced when amino acids were added during HA preparation. Depending on the types of amino acid, the specific surface area of the amino acid-functionalized HA particles varied from 105 to 149 m 2 g –1 . Bovine serum albumin (BSA) and lysozyme were used as model proteins for adsorption study. The protein adsorption onto the surface of amino acid-functionalized HA depended on the polarities of HA particles, whereby, compared with lysozyme, BSA demonstrated higher affinity towards positively charged Arg-HA. Alternatively, the binding affinity of lysozyme onto the negatively charged Asp-HA was higher when compared with BSA. The BSA and lysozyme adsorptions onto the amino acid-functionalized HA fitted better into the Freundlich than Langmuir model. The amino acid-functionalized HA particles that had higher protein adsorption demonstrated a lower protein-release rate.

scholarly journals Conformational analysis of 2,2-difluoroethylamine hydrochloride: double gauche effect

2014 ◽  
Vol 10 ◽  
pp. 877-882 ◽  
Author(s):  
Josué M Silla ◽  
Claudimar J Duarte ◽  
Rodrigo A Cormanich ◽  
Roberto Rittner ◽  
Matheus P Freitas
Keyword(s):  
Hydrogen Bond ◽  
Electrostatic Interactions ◽  
Fluorine Atom ◽  
Theoretical Calculations ◽  
Water Solution ◽  
Coupling Constants ◽  
Secondary Importance ◽  
Gauche Effect ◽  
Intramolecular Hydrogen ◽  
Positively Charged

The gauche effect in fluorinated alkylammonium salts is well known and attributed either to an intramolecular hydrogen bond or to an electrostatic attraction between the positively charged nitrogen and the vicinal electronegative fluorine atom. This work reports the effect of adding a fluorine atom in 2-fluoroethylamine hydrochloride on the conformational isomerism of the resulting 2,2-difluoroethylamine chloride (2). The analysis was carried out using NMR coupling constants in D2O solution, in order to mimic the equilibrium conditions in a physiological medium, in the gas phase and in implicit water through theoretical calculations. Despite the presence of σCH→σ*CF and σCH→σ*CN interactions, which usually rule the hyperconjugative gauche effect in 1,2-disubstituted ethanes, the most important forces leading to the double gauche effect (+NH3 in the gauche relationship with both fluorine atoms) in 2 are the Lewis-type ones. Particularly, electrostatic interactions are operative even in water solution, where they should be significantly attenuated, whereas hyperconjugation and hydrogen bond have secondary importance.

scholarly journals Mechanism and site of action of big dynorphin on ASIC1a

2019 ◽  
Author(s):  
C.B. Borg ◽  
N. Braun ◽  
S.A. Heusser ◽  
Y. Bay ◽  
D. Weis ◽  
...  
Keyword(s):  
Amino Acids ◽  
Ischemic Stroke ◽  
Amino Acid ◽  
Binding Site ◽  
Neuronal Death ◽  
Electrostatic Interactions ◽  
Rational Design ◽  
Site Of Action ◽  
Canonical Amino Acid

AbstractAcid-sensing ion channels (ASICs) are proton-gated cation channels that contribute to neurotransmission, as well as initiation of pain and neuronal death following ischemic stroke. As such, there is a great interest in understanding the in vivo regulation of ASICs, especially by endogenous neuropeptides that potently modulate ASICs. The most potent endogenous ASIC modulator known to date is the opioid neuropeptide big dynorphin (BigDyn). BigDyn is upregulated in chronic pain and increases ASIC-mediated neuronal death during acidosis. Understanding the mechanism and site of action of BigDyn on ASICs could thus enable the rational design of compounds potentially useful in the treatment of pain and ischemic stroke. To this end, we employ a combination of electrophysiology, voltage-clamp fluorometry, synthetic BigDyn analogs and non-canonical amino acid-mediated photocrosslinking. We demonstrate that BigDyn binding results in an ASIC1a closed resting conformation that is distinct from open and desensitized states induced by protons. Using alanine-substituted BigDyn analogs, we find that the BigDyn modulation of ASIC1a is mediated through electrostatic interactions of basic amino acids in the BigDyn N-terminus. Furthermore, neutralizing acidic amino acids in the ASIC1a extracellular domain reduces BigDyn effects, suggesting a binding site at the acidic pocket. This is confirmed by photocrosslinking using the non-canonical amino acid azido-phenylalanine. Overall, our data define the mechanism of how BigDyn modulates ASIC1a, identify the acidic pocket as the binding site for BigDyn and thus highlight this cavity as an important site for the development of ASIC-targeting therapeutics.Significance StatementNeuropeptides such as big dynorphin (BigDyn) play important roles in the slow modulation of fast neurotransmission, which is mediated by membrane-embedded receptors. In fact, BigDyn is the most potent known endogenous modulator of one such receptor, the acid-sensing ion channel (ASIC), but the mode of action remains unknown. In this work, we employ a broad array of technologies to unravel the details of where big dynorphin binds to ASIC and how it modulates its activity. As both BigDyn and ASIC are implicated in pain pathways, this work might pave the way towards future analgesics.

Tetraphenyl porphyrin films as selective detectors for amino acid molecules

2020 ◽  
Vol 24 (10) ◽  
pp. 1215-1223
Author(s):  
Jesús Miguel Rivera ◽  
Margarita Rivera
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Quartz Crystal Microbalance ◽  
Quartz Crystal ◽  
Binding Energies ◽  
Charged Amino Acids ◽  
Tetraphenyl Porphyrin ◽  
Pseudo Second Order ◽  
Selective Detectors ◽  
Positively Charged

The interaction of different amino acids and vacuum evaporated tetraphenyl porphyrin films was investigated by using kinetic isotherms, UV-vis spectroscopy, quartz crystal microbalance and density functional theory techniques. The adsorption process was analyzed by using pseudo-first-order and pseudo-second-order models. From these results, the adsorption order changed depending on the chemical characteristics of the porphyrin film, although most of the interactions were classified as pseudo-second-order at the films interface. From absorbance measurements, red shifts on the Soret peak positions were observed for all amino acids interacting with the metal free and the ZnTPP systems, while the position of the Soret peak barely change for the CuTPP surface, except for a slight bathocromic shift for arginine. On the other hand, the broadening of the Soret peak was more important for the ZnTPP and H2TPP surfaces, but the interaction with the CuTPP interfaces decreased the width of the peaks in all cases. In addition, a quartz crystal microbalance analysis was employed to investigate the film sensing performance during amino acid exposure. From these results, positively charged amino acids were more easily adsorbed on the films in contrast with the polar (serine) molecule. DFT calculations exhibited important deformations for H2TPP, the out-of-plane displacement of the Zn atom for ZnTPP, and hydrogen bond interactions with the CuTPP molecule. DFT also showed high binding energies for the positively charged amino acids but low binding energies for serine in agreement with experimental data. From these results, porphyrin films could be used as selective detectors for various L-amino acid molecules.

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