Determination aminoacids

Since the binding of extraneous ions considerably alters the value of lEP of an aminoacid or protein, this point is not a constant. The term isoionic point (IP) is used to designate the pH value of a pure protein in salt-free water. The direct determination of this constant is difficult and because many proteins are insoluble in the absence of salts. The isoionic point is usually determined indirectly, that is, by measuring the lEP at different concentrations of the neutral salts and extrapolating to zero concentration The value of the isoionic point may differ from lEP by more than a pH unit (Haurowitz 1963). 

M3. Moore, S., and Stein, W. H., Procedures for the chromatographic determination of aminoacids on four per cent cross-linked sulfonated polystyrene resins. J. Biol. Chem. 211, 893-906 (1954). 

On-line anion exchange LC/ICP-MS methods for selenium and chromium speciation have been published [30], In studies of selenium speciation in environmental samples LC/ICP-MS and LC/ ESI-MS methods have been used for the determination of both inorganic and organic selenium species [43]. For the determination of methyl selenide, strong anion exchange and RP chromatography have been employed [43], while for the determination of seleno-aminoacids, IP RP chromatography with on-line detection based on ICP-MS has been successfully employed [44],... 

Present-day diffraction facilities provide easy access to very low-temperature data collection and hence to an accurate determination of electron densities in crystals. Application of standard theorems of classical physics then provides an evaluation of the Coulombic interaction energies in crystal lattices [27]. These calculations are parameter-less and hence are as accurate as the electron density is. Moreover, for highly polar compounds, typically aminoacid zwitterions and the like, a fortunate coincidence cancels out all other attractive and repulsive contributions, and the Coulombic term almost coincides with the total interaction energy. 

Copper has been employed commonly in relation with carbohydrates and aminoacids but other analytes can also be determined. Microalignment of the electrode with the channel outlet [89], deposition of a thin layer [81,108] or incorporation of a wire [21] are examples of in-channel formats. End-channel configurations such as those obtained by using a guide tube [11] or attaching a Cu wire perpendicularly to the outlet [32] after chip bonding were tested. Carbon nanotube (CNT)/copper composite electrodes have proved to be more sensitive, compared to the Cu and CNT alone, in the determination of carbohydrates [109]. 

Moreover, the isomeric distributions of aminoacids and hydroxyacids seem to suggest that radical reactions, must also be taken into account (see paragraph 5.4). Presently, it remains impossible to determine if this kind of processes played a role during the accretion process or later. 

D20. Dern, P. L., Aminoaciduria with cystinosis case report with determination of urinary aminoacids and ocular cystine. Ann. Internal Med. 46, 138-144 (1957). 

F8. Folin, O., A colorimetric determination of the aminoacid nitrogen in normal urine. /. Biol. Chem. 51, 393-394 (1922). 

M22. Moubasher, R., and Sina, A., The gasometric determination of a-aminoacids by the peri-naphthindan-2,3,4-trione hydrate. Carbon dioxide method in pure solutions with remarks upon its use in blood and urine. J. Biol. Chem. 180, 681-688... 

Fig. 5.1 The protein chain in atomic resolution. The chain consists of quasi-planar (nearly rigid) peptide bonds -NH-CO- connected by the C atoms. Each Ca atom has additionally the CH and CR bond, where R is the aminoacid side chain (one of the twenty used by nature). The figure shows also the 4>, / angles (corresponding to a single amino acid). The conformation of the whole chain is determined by a set of , x(/, angles, where i means the z th amino acid...

The last subject in the discussion of inherently chiral compounds deals with the analysis of the aminoacids, peptides, and proteins. Most all of the remarks that were made about the steroids and carbohydrates regarding CD detection apply equally well to these. The enantiomeric purity of aminoacids is usually determined by their optical rotations at the sodium-D line. Rotations are normally so small that concentrated solutions and long pathlengths are needed. The detection is enhanced a little if laser illumination is used [66] or if ORD detection is done around 230 nm [71]. Without derivatization, only aminoacids with aromatic substituents are CD active in the near UV. Signals are generally weak and enantiomeric purity measurements are not quantitative. 

The sequence of nucleotides in w-RNA apparently determines the order in which aminoacids appear in a protein. It is currently assumed that a codon", i.e., a sequence of three nucleotides in w-RNA, associates with a trinucleotide group (designated as "anticodon") of the s-RNA. 

Aminoacid-tRNA synthetases were isolated from spinach chloroplasts by methods developed at Jealott s Hill. Cytoplasmic aaTRS s from carrot were isolated by standard procedures. Compounds were assayed as inhibitors of the chloroplastic aaTRS s at a single rate, 10 pM. The reaction was followed by phosphate generation and the percentage inhibition determined using literature methods. The IC50 value for the spinach chloroplastic enzymes and inhibition data for carrot cytoplasmic aaTRS s were determined for compounds of interest. All compounds were tested for post-emergence herbicidal activity, at 0.125, or at 0.5, or at 2.0 k a in standard screens." ... 

A curious method for determining the enzymatic activity of trypsin and of the duodenal content has been demonstrated on the cleavage of p-nitroanilides of some aminoacids [180]. The half-wave potential of p-nitroaniline reduction is more negative than that of the substituted derivatives and so the hydrolysis of the nitroanilides can be measured by the decrease of its reduction wave. 

Several studies were undertaken in order to investigate in more detail the nature of the antiviral compounds and their mechanisms of action. Structures of active pure compounds have been determined as PS, steroids, aminoacid derivatives, diterpenes, lipids and alkaloids. 

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