Isoelectric Point Of Amino Acid Research Articles

Accurate Estimation of pKb Values for Amino Groups from Surface Electrostatic Potential (VS,min) Calculations: The Isoelectric Points of Amino Acids as a Case Study.

Theoretical calculation of equilibrium dissociation constants is a very computationally demanding and time-consuming process since it requires an extremely accurate computation of the solvation free energy changes for each of the species involved. By correlating the minimum surface electrostatic potential (VS,min) on the nitrogen atom of several aliphatic amino groups-calculated at the density functional theory (DFT) ωB97X-D/cc-pVDZ level of theory-we obtained regression models for each kind of substitution pattern from which we interpolate their corresponding pKb values with remarkable accuracy: primary R2 = 0.9519; secondary R2 = 0.9112; and tertiary R2 = 0.8172 (N = 20 for each family). These models were validated with tests sets (N = 5) with mean absolute error (MAE) values of 0.1213 (primary), 0.4407 (secondary), and 0.3057 (tertiary). Combining this ansatz with another previously reported by our group to estimate pKa values [Caballero-García, G.; et al. Molecules 2019, 24(1), 79] we are able to reproduce the isoelectric points of 13 amino acids with no titrable side chains with MAE = 0.4636 pI units.

Influence of the nature of amino acids on the formation of mesoporous LTA-type zeolite

Hydrothermal crystallization of LTA zeolite has been conducted in the presence of amino acid in order to introduce mesoporosity. Eight different types of proteinogenic amino acids have been employed. The influence of their structure and physicochemical properties on the formation of hierarchically mesoporous LTA (MLTA) zeolite have been investigated. All eight amino acids bearing either basic, or acidic, or polar non-ionizable, or non-polar non-ionizable side chains were able to generate mesopores within LTA crystals. The isoelectric points of amino acids influenced the resulting MLTA's morphology, crystallization kinetics, and impurity content. Pure phase MLTA with controllable shape was obtained. Amino acid with a higher isoelectric point generated smaller and more spherical MLTA in less crystallization time, but induced slightly more impurity FAU phase. The mesopore size generally decreased with hydropathy index so that amino acids with non-polar, non-ionizable side groups generated 14–15 nm mesopores, 5–10 nm smaller than those generated by amino acids in other categories. The hydrophobic moieties in amino acids tended to shrink the mesopores, in contrast with their pore expansion effect in surfactant-mediated mesopore generation route, suggesting a different mesopore formation mechanism. Stability of amino acid during the hydrothermal zeolite synthesis and easy amino acid removal by washing with water was further confirmed. The findings discovered in this study paves a new way for tailoring hierarchical zeolite materials with controlled texture properties.

The effect of antioxidants on quantitative changes of lysine and methionine in linoleic acid emulsions at different pH conditions.

Plants are an important source of phenolic compounds. The antioxidant capacities of green tea, thyme and rosemary extracts that contain these compounds have been reported earlier. However, there is a lack of accessible information about their activity against lipid oxidation in emulsions and inhibit the interaction of lipid oxidation products with amino acids. Therefore, the influence of green tea, thyme and rosemary extracts and BHT (butylated hydroxytoluene) on quantitative changes in lysine and methionine in linoleic acid emulsions at a pH of isoelectric point and a pH lower than the isoelectric point of amino acids was investigated. Total phenolic contents in plant extracts were determined spectrophotometrically by using Folin-Ciocalteu's reagent, and individual phenols by using HPLC. The level of oxidation of emulsion was determined using the measurement of peroxides and TBARS (thiobarbituric acid reactive substances). Methionine and lysine in the system were reacted with sodium nitroprusside and trinitrobenzenesulphonic acid respectively, and the absorbance of the complexes was measured. Extract of green tea had the highest total polyphenol content. The system containing antioxidants and amino acid protected linoleic acid more efficiently than by the addition of antioxidants only. Lysine and methionine losses in samples without the addition of antioxidants were lower in their isoelectric points than below these points. Antioxidants decrease the loss of amino acids. The protective properties of antioxidants towards methionine were higher in a pH of isoelectric point whereas towards lysine in pH below this point. Green tea, thyme and rosemary extracts exhibit antioxidant activity in linoleic acid emulsions. Moreover, they can be utilized to inhibit quantitative changes in amino acids in lipid emulsions. However, the antioxidant efficiency of these extracts seems to depend on pH conditions. Further investigations should be carried out to clarify this issue.

Chemical components and emulsification properties of mucilage from Dioscorea opposita Thunb.

The properties of mucilage obtained from Dioscorea opposita, generated during industrial manufacturing were investigated in this study. Characteristics such as monosaccharide content, amino acid content, molecular weight, and structural features were measured, whereas morphology was observed using a scanning/transmission electron microscope. Additionally, emulsification properties at different concentrations (0.2%, 0.4%, 0.6%, 0.8%, and 1.0%) and under acidic and basic pH (5.0 and 9.0) conditions were studied. The results showed that emulsions prepared from mucilage and medium-chain triglycerides presented more effective emulsifying functions and higher stability, especially at low concentrations. Both, acidic and basic conditions improved the overall emulsification properties, which suggested that the isoelectric point of amino acids may be involved in the emulsification properties. The results of this study show that mucilage from Dioscorea opposita can be considered as a sustainable resource of a natural emulsifier obtained from industrial waste.

Isoelectric point of amino acid: Importance for monascus pigment production

Abstract This study aimed to determine the effect of pH on radial growth rate and pigments production from Monascus ruber CCT 3802. Fermentations were carried out in solid medium and submerged fermentations under different pH conditions and the pigments produced were submitted to scanning in spectrophotometer. Higher radial growth rate was obtained when M. ruber was growing at pH 4.0 and the production of yellow pigment was obtained at low pH (2.0–3.0), while the production of orange and red pigments were in the pH range from 3.0 to 4.0 and above of 5.0, respectively. The results showed that pH has a significant influence on the radial growth rate, pigment production and particularly on the profile of orange and red pigments. pH proved to be an extremely important factor for obtaining orange (precursor) or red pigment, since the isoelectric point of NH 3 + sources is critical to converting orange pigment into red pigment.

Sequence Perturbation Analysis: Addressing Amino Acid Indices to Elucidate the C-Terminal Role of Escherichia Coli Dihydrofolate Reductase

Because amino acid residues intrinsically possess many factors participating in protein structures and functions, to determine main (or unique) factors at a specific site in a protein sequence should be of great help for understanding how a protein obtains its structure and function. In this study, we proposed a means of sequence perturbation analysis to address the above concerns involving comprehensive AA indices. We constructed all 19 possible single mutant proteins as to the three sites in the C-terminal of Escherichia coli dihydrofolate reductase (DHFR), and measured the activity and thermal stability of each of all the single mutant proteins. The significantly perturbed properties with each systematic single mutation at each mutational site were examined in terms of the linear correlation with each AA index. As a result, at each of Arg158 and Arg159 of DHFR, the AA index for the isoelectric points of amino acids showed strong correlation with the transition temperature of thermal denatuation, suggesting that the electrostatic interaction is the main factor influencing the C-terminal role of the DHFR. The feasibility and general versatility of our sequence perturbation analysis were also examined by application to other sites of DHFR.

Effects of amino acids on crystal growth of CaC 2O 4 in reverse microemulsion

Crystal growth of calcium oxalate (CaC 2O 4) in bulk aqueous solution, reverse microemulsion of p-octyl polyethylene glycol phenylether (OP)/ iso-octyl alcohol (IOA)/cydohexane/water and above microemulsions containing different kinds of amino acids, such as aspartic acid (Asp), tyrosine (Tyr) and tryptophan (Trp) were studied. The results indicated that different crystallization types of the crystals, which were calcium oxalate monohydrate (COM), calcium oxalate dihydrate (COD) and calcium oxalate trihydrate (COT), existed in bulk aqueous solution. But CaC 2O 4 growth mainly paralleled with ( 1 ¯ 0 1 ) plane of COM in reverse microemulsion because of the induction of surfactant at water/oil interface. After adding amino acids into microemulsions, the growth of CaC 2O 4 crystals mainly influenced by the varieties of amino acids and the pH values of the amino acid aqueous solution. When pH values of the solutions was higher than isoelectric points of amino acids, CaC 2O 4 crystal paralleled with ( 1 ¯ 0 1 ) plane of COM more easily with the addition of Trp, Tyr, Asp in turn; however, when pH of the solutions was lower than isoelectric points of Trp, CaC 2O 4 crystal growth paralleled with (0 2 0) face of COM. It is obviously that amino acids, pH values of the solutions and surfactant played important roles in the process of crystal growth of CaC 2O 4 in the microemulsions. The formation mechanism of CaC 2O 4 was also discussed in different microemulsions at last.

Structuring of the genetic code took place at acidic pH

I have observed that in multiple regression the number of codons specifying amino acids in the genetic code is positively correlated with the isoelectric point of amino acids and their molecular weight. Therefore basic amino acids are, on average, codified in the genetic code by a larger number of codons, which seems to imply that the genetic code originated in an acidic ‘intracellular’ environment. Moreover, I compare the proteins from Picrophilus torridus and Thermoplasma volcanium, which have different intracellular pH and I define the ranks of acidophily for the amino acids. A simple index of acidophily (AI), which can be easily obtained from acidophily ranks, can be associated to any protein and, therefore, can also be associated to the genetic code if the number of synonymous codons attributed to the amino acids in the code is assumed to be the frequency with which the amino acids appeared in ancestral proteins. Finally, the sampling of the variable AI among organisms having an intracellular pH less than or equal to 6.6 and those having a non-acidic intracellular pH leads to the conclusion that the value of the genetic code's AI is not typical of proteins of the latter organisms. As the genetic code's AI value is also statistically not different from that of proteins of the organisms having an acidic intracellular pH, this supports the hypothesis that the structuring of the genetic code took place in acidic pH conditions.

Study on the isotherms of the interaction between suspended particles and Cu (II) in the Huanghe River

The isotherms of the interaction between the suspended particles and Cu2+, and the effects of lysine and asparaginic acid on the isotherms in the Huanghe (Yellow) River were studied by applying the theory and method of interfacial stepwise ion/coordination particle exchange. We obtained a new stepped river isotherm, formed by two curves joined together with a “plateau” in the middle. The adsorption equilibrium constantsK 1 andK 2 were calculated by using the isothermal equation of surface stepwise ion exchange. Amino acid in small amount promotes exchange adsorption of the suspended particles with Cu2+. The degree of promotive action relates to the isoelectric point of amino acid. The promotive effect of lysine is bigger than that of asparaginic acid.

Separation of bonito extract by composite UF membranes of sulfonated polysulfone coated on ceramics

Separation of ingredients in bonito extract was studied by a composite UF membrane of ceramic/sulfonated polysulfone (SPS). The bonito extract mainly contained inosine-5′-monophosphate (IMP), glutamic acid as a tasty ingredient and hypoxanthine, histidine as a putrefaction ingredient. The composite membrane showed a high rejection against negatively charged IMP, but permeated non-charged hypoxanthine. This is because of the negatively charged repulsion between the membrane and the solute. The permeation of amino acid could be controlled using the difference in isoelectric points of amino acids themselves. When the amino acid solution was filtrated by the composite membrane at pH 7, glutamic acid was rejected and no histidine was rejected. The charges of composite membrane were found to have an effect on the separation of ingredients in bonito extract. The composite membrane was stable within a wide pH range from 3 to 9, and had a thermal durability under 353 K.

Molecular Connectivity Model for Determination of Isoelectric Point of Amino Acids

A molecular connectivity model for the calculation of the isoelectric point of amino acids is presented. The model requires calculation of the molecular connectivity values of only the functional fragments of the amino acids. Multiple linear regression with two variables shows the best fit between experimental and calculated data.

Complex Formation between Synthetic Sodium Taeniolite and Amino Acids

合成ナトリウム型テニオライト[NaMg2Li(Si,O,e)F](N-T)カミ膨潤性を有する点に着目して,N-Tと各種アミノ酸との複合体の生成を試みた。その結果,各アミノ酸の等電点よりも酸性側に調製した塩酸酸性アミノ酸水溶液でN-Tを処理することにより,アミノ酸分子がN-Tの層間に侵入配位し,N-T-アミノ酸複合体が生成することが判明した。pH=1で調製した各種複合体の層間二値[d(OOI)]の測定結果から,これら複合体の層間におけるアミノ酸分子の配列の様式を検討し,炭素数の小さいアミノ酸(炭素数=3．4)ではアミノ酸のアルキル鎖がケイ酸層に平行に並んだいわゆるa型をとって一分子層配列をなしていることが判明した。このような複合体生成はおもにN-Tの層間Na+イオンとアミノ酸陽イオンとのイオン交換機構によって起こる。なお,これら複合体の加熱変化およびN-Tからの水素型テニオライト(H-T)の生成についても述べた。

Paper disk electrophoresis in the determination of isoelectric points of amino acids

A method is described for studying the mobility of different amino acids in buffer solutions of different pH using the paper disk electrophoretic apparatus. From the mobility of amino acids the isoelectric point of individual amino acids has been calculated. The results obtained are in good agreement with those obtained by others.