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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.
The 21 proteinogenic α-amino acids found in eukaryotes, grouped according to their side chains' pK a values and charges carried at physiological pH (7.4) 2-, alpha-, or α-amino acids [21] have the generic formula H 2 NCHRCOOH in most cases, [b] where R is an organic substituent known as a "side chain". [22]
In approximately neutral aqueous solution (pH ≅ 7), the basic amino group is mostly protonated and the carboxylic acid is mostly deprotonated, so that the predominant species is the zwitterion H 3 N + −RCH−COO −. The pH at which the average charge is zero is known as the molecule's isoelectric point.
It is different from the isoelectric point (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 at net charge zero in a deionized solution. Thus, the isoelectric and isoionic points are equal when the concentration of charged species is zero.
The isoelectric point of casein is 4.6. Since milk's pH is 6.6, casein has a negative charge in milk. The purified protein is water-insoluble. While it is also insoluble in neutral salt solutions, it is readily dispersible in dilute alkalis and in salt solutions such as aqueous sodium oxalate and sodium acetate.
It works on almost any kind of charged molecule—including small inorganic anions, [2] large proteins, [3] small nucleotides, [4] and amino acids. However, ion chromatography must be done in conditions that are one pH unit away from the isoelectric point of a protein. [5] The two types of ion chromatography are anion-exchange and cation-exchange.
Glycine (symbol Gly or G; [6] / ˈ ɡ l aɪ s iː n / ⓘ) [7] is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid (carbamic acid is unstable). Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (GGU, GGC, GGA, GGG). [8]
β-Alanine (beta-alanine) is a naturally occurring beta amino acid, which is an amino acid in which the amino group is attached to the β-carbon (i.e. the carbon two carbon atoms away from the carboxylate group) instead of the more usual α-carbon for alanine (α-alanine). The IUPAC name for β-alanine is 3-aminopropanoic acid.