Amino acid electrolyte properties

The major important organic electrolytes and nonelectrolytes transported by epithelial cells include sugars, amino acids, nucleosides, organic cations, and organic anions. Transport systems have significant implications for the absorption, distribution, elimination, and pharmacokinetic properties of many clinically important drugs. The major epithelial tissues... 

Isoelectric point,/ / the pH value of a solution at which the net charge on the dissolved ampholyte is zero, i.e. the sum of the cationic charges is equal to the sum of the anionic charges. The pi of electrolytes, e.g. amino acids, peptides or proteins, may lie in the range from pH 1 ( psin) to pH 11.8 (protamine), and is characteristic for each amphol e. Certain characteristic properties appear at the pi, e.g. a minimal solubility and viscosity. Electrophoretic methods of separation arc based on the differences in the pi of the individual components. The pi. can be determined either electrophoretically at various pH values or by electrofocusing on an ampholine pH adient. 

This is a general and extensive review dealing with differences in thermodynamic properties between light and heavy water systems. The properties dealt with include Gibbs energies and enthalpies of transfer and solubilities systems for which data are tabulated include the more common inorganic electrolytes and ions, alcohols, amides, amino acids, and several nonelectrolytes. 

Another characteristic property of this type of adsorption is the marked dependence of electrolyte concentration, which is particularly noticeable for adsorbents of the aluminum oxide type. This complicatea the situation because it may make it difficult to apply buffer solutions which otherwise would be desirable to maintain a defined pH throughout the separation. There are not yet any detailed systematic investigations on the adsorption of ampholytes on exchange adsorbents under sufficiently varied conditions (particularly pH and electrolytes should be varied), but a large amount of empirical data have been collected in connection with the recent attempts to use these adsorbents for the separation of amino acids, showing the differences in behavior for different amino acids. The reader is referred especially to the recent papers by Englis and Fiess (1944) and by Cleaver, Hardy and Cassidy (1945). 

Detection of metallothionein is connected with specific structure of MT, i.e. the absence of aromatic amino acids in the native state and disulfide bonds. However, its structure is adapted to incorporate heavy metal ions by sulfhydryl groups, thus, these specific features may be used for the electrochemical determination. The protection by reduction agents is required, because sulfbydryl groups have a tendency to be oxidized. On the other hand, this property allows an application of electrochemical determination. The other opportunity how to detect metallothionein is the catalysis of hydrogen evolution from a supporting electrolyte [38-41]. 

Dipolai Form of the Amino Acids.—The monoamino-monocarboxy acids are neutral in solution, and are very weak electrolytes. At the same time they are able to neutralise either acids or bases. This property, termed amphotericity, is due to the presence of an acid and a basic group in the same molecule. In aqueous solutions amino acids ionise to form a dipolar or zwitter-ion, having two equal charges of opposite electric sign, and tending to migrate neither to anode nor cathode when a current is passed through the solution. 

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