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The isoelectric point (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean. The standard nomenclature to represent the isoelectric point is pH(I). [1] However, pI is also used. [2] For brevity, this article uses pI.
In computational biology, protein pK a calculations are used to estimate the pK a values of amino acids as they exist within proteins.These calculations complement the pK a values reported for amino acids in their free state, and are used frequently within the fields of molecular modeling, structural bioinformatics, and computational biology.
[72] [73] [74] The isoelectric point of a given molecule is a function of its pK values, so different molecules have different isoelectric points. This permits a technique called isoelectric focusing , [ 75 ] which is used for separation of proteins by 2-D gel polyacrylamide gel electrophoresis .
The two dimensions that proteins are separated into using this technique can be isoelectric point, protein complex mass in the native state, or protein mass. [citation needed] The separation by isoelectric point is called isoelectric focusing. Thereby, a pH gradient is applied to a gel and an electric potential is applied across the gel, making ...
The iso-electric point is the pH value at which the zeta potential is approximately zero. At a pH near the iso-electric point (± 2 pH units), colloids are usually unstable; the particles tend to coagulate or flocculate. Such titrations use acids or bases as titration reagents. Tables of iso-electric points for different materials are available ...
Amino acids have zero mobility in electrophoresis at their isoelectric point, although this behaviour is more usually exploited for peptides and proteins than single amino acids. Zwitterions have minimum solubility at their isoelectric point, and some amino acids (in particular, with nonpolar side chains) can be isolated by precipitation from ...
Free-flow electrophoresis (FFE), also known as carrier-free electrophoresis, is a matrix-free, high-voltage electrophoretic separation technique. FFE is an analogous technique to capillary electrophoresis, with a comparable resolution, that can be used for scientific questions, where semi-preparative and preparative amounts of samples are needed.
At the isoelectric point the relationship between the dielectric constant and protein solubility is given by: log S = k / e 2 + log S 0 {\displaystyle \log S=k/e^{2}+\log S^{0}\,} S 0 is an extrapolated value of S , e is the dielectric constant of the mixture and k is a constant that relates to the dielectric constant of water.