pH at which a particular molecule, or the surface of a given solid, carries no net electrical charge
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. The net charge on the molecule is affected by pH of its surrounding environment and can become more positively or negatively charged due to the gain or loss, respectively, of protons (H+).
Surfaces naturally charge to form a double layer. In the common case when the surface charge-determining ions are H+/HO−, the net surface charge is affected by the pH of the liquid in which the solid is submerged.
The pI value can affect the solubility of a molecule at a given pH. Such molecules have minimum solubility in water or salt solutions at the pH that corresponds to their pI and often precipitate out of solution. Biological amphoteric molecules such as proteins contain both acidic and basic functional groups. Amino acids that make up proteins may be positive, negative, neutral, or polar in nature, and together give a protein its overall charge. At a pH below their pI, proteins carry a net positive charge; above their pI they carry a net negative charge. Proteins can, thus, be separated by net charge in a polyacrylamide gel using either preparative native PAGE, which uses a constant pH to separate proteins, or isoelectric focusing, which uses a pH gradient to separate proteins. Isoelectric focusing is also the first step in 2-D gel polyacrylamide gel electrophoresis.
In biomolecules, proteins can be separated by ion exchange chromatography. Biological proteins are made up of zwitterionic amino acid compounds; the net charge of these proteins can be positive or negative depending on the pH of the environment. The specific pI of the target protein can be used to model the process around and the compound can then be purified from the rest of the mixture. Buffers of various pH can be used for this purification process to change the pH of the environment. When a mixture containing a target protein is loaded into an ion exchanger, the stationary matrix can be either positively-charged (for mobile anions) or negatively-charged (for mobile cations). At low pH values, the net charge of most proteins in the mixture is positive – in cation exchangers, these positively-charged proteins bind to the negatively-charged matrix. At high pH values, the net charge of most proteins is negative, where they bind to the positively-charged matrix in anion exchangers. When the environment is at a pH value equal to the protein's pI, the net charge is zero, and the protein is not bound to any exchanger, and therefore, can be eluted out.[3]
^Acceptable variants on pH(I) would include pHI, pHIEP, etc; the main point is that one cannot take the 'power' of I, rather one measures the pH subject to a nominated condition.
^IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "isoelectric point in electrophoresis". doi:10.1351/goldbook.I03275
^Dayton, W. R. (1983). "Protein Separation Techniques" (PDF). Reciprocal Meat Conference Proceedings. 36: 98–102.
The isoelectricpoint (pI, pH(I), IEP), is the pH at which a molecule carries no net electrical charge or is electrically neutral in the statistical mean...
Isoelectric focusing (IEF), also known as electrofocusing, is a technique for separating different molecules by differences in their isoelectric point...
salt effect (pzse), zero point of titration (zpt) of colloidal dispersion, and isoelectricpoint of the solid (ieps) and point of zero surface tension...
Isoelectric may refer to: Isoelectricpoint, the pH at which a particular molecule carries no net electrical charge Isoelectric focusing, a technique...
disorder. The isoelectricpoint of a given molecule is a function of its pK values, so different molecules have different isoelectric points. This permits...
net charge of all forms present is zero. This pH is known as the isoelectricpoint pI, so pI = 1/2(pKa1 + pKa2). For amino acids with charged side chains...
disadvantage to isoelectricpoint precipitation is the irreversible denaturation caused by the mineral acids. For this reason isoelectricpoint precipitation...
maintains its activity in a large range of pH (6–9). Its isoelectricpoint is 11.35. The isoelectricpoint of human milk lysozyme is 10.5–11. The enzyme functions...
is known as the molecule's isoelectricpoint. Ampholytes are used to establish a stable pH gradient for use in isoelectric focusing. Metal oxides which...
according to isoelectricpoint, while in the second dimension, polypeptides are separated according to their molecular weight. The isoelectricpoint of a given...
whey protein is covering the casein micelle, isoelectricpoint of the micelle elevated to the isoelectricpoint of β lactoglobulin (approximately pH 5.3)...
chromatography must be done in conditions that are one pH unit away from the isoelectricpoint of a protein. The two types of ion chromatography are anion-exchange...
region of the midbrain in the house mouse (Mus musculus) brain. The isoelectricpoint of the EVA1C protein in humans (Homo sapiens) is 6.5 pl and the molecular...
help bring the proteins near their isoelectricpoint to allow them to be denatured easier. The isoelectricpoint is a specific pH where a molecule, in...
separated along with the anions based on their isoelectricpoint (pI). In proteins, the isoelectricpoint (pI) is defined as the pH at which a protein has...
(126–145 °F)[citation needed] at the moment the cheese is at the isoelectricpoint, meaning the state at which half the ionizable surface amino acids...
might change the size or isoelectricpoint of proteins. The binary shifts might be left to right (change in isoelectricpoint), vertical (change in size)...
Its main function is to regulate the oncotic pressure of blood. The isoelectricpoint of albumin is 4.7. Alpha-fetoprotein is a fetal plasma protein that...
Archived from the original on 15 June 2012. Retrieved 17 May 2012. For isoelectricpoint: Gayer, K. H.; Thompson, L. C.; Zajicek, O. T. (September 1958). "The...
the egg white proteins are near their isoelectric points. Protein adsorption is most rapid at the isoelectricpoint because electrostatic repulsion is reduced...
certain high ionic strength of a salt solution that should have a high isoelectricpoint as well which should be around 9.05 to 9.26 pI. This type of globulin...
known as drilling mud – Aid for drilling boreholes into the ground Isoelectricpoint – pH at which a particular molecule, or the surface of a given solid...
gel electrophoresis if the desired protein's molecular weight and isoelectricpoint are known, by spectroscopy if the protein has distinguishable spectroscopic...
isoelectricpoint (pI) in that pI is the pH value at which the net charge of the molecule, including bound ions is zero. Whereas the isoionic point is...
charge on the protein molecules, and brings them closer to their isoelectricpoint. This results in a stronger, more stable inter-facial film. When added...
are predicted to also have a high abundance of proline. The basal isoelectricpoint for PRR23C Homo sapiens was 4.48 (pH) according to phoshosite.org...
Global Information