Isoelectric Point


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isoelectric point

[¦ī·sō·i′lek·trik ′pȯint]
(physical chemistry)
The pH value of the dispersion medium of a colloidal suspension at which the colloidal particles do not move in an electric field.

Isoelectric Point

 

(point of zero charge), the state of the surface of a body or of a particle in the dispersed phase in contact with an electrolytic solution; it is characterized by an equal number of positive and negative charges in the adsorption layer. Here the zeta potential is equal to zero. Colloidal systems stabilized by electrolytes are unstable at the isoelectric points—that is, they break down as a result of the adhesion of particles in the dispersed phase. The electrically neutral state of amphoteric electrolytes (ampholytes) that contain separate acid and base groups is also called the isoelectric point. A specific pH value corresponds to the isoelectric point of every ampholyte. At the isoelectric point the molecules of ampholyte, like colloidal particles, lose the ability to shift directionally in an electrical field. The swelling, solubility, and viscosity of solutions and many other characteristics of ampholytes, particularly macromolecular ampholytes, assume extreme values as the isoelectric point is approached.

References in periodicals archive ?
ABREVIATIONS: 2-DE= two-dimensional electrophoresis; IPG = immobilized pH gradient; MALDI-TOF = matrix assisted laser desorption ionization time-of-flight; mRNA = messenger ribonucleic acid; pI = isoelectric point.
Degree of polymerization (DP), Zeta potential ([zeta]), Isoelectric point (IEP) and Point of zero charge (PZC) of cotton fabrics [zeta] at pH 10 IEP PZC q Fabric DP [mV] [pH] [[micro]g/ml] [C/g] R 2201,02 -11,1 <2,5 94,57 -2,43 D 2159,37 -12,5 <2,5 85,19 -2,40 AS 1987,23 -17,3 2,95 76,82 -2,36 ES1 2056,20 -18,1 2,92 75,68 -2,32 ES2 2151,98 -18,5 2,93 73,21 -2,29 Table 3.
These isoenzymes can be distinguished by their isoelectric points (p1) and are thought to perform different functions in different tissues at different times in plant d evelopment.
Prediction of isoelectric points of legume and oil seed proteins from their amino acid compositions.
Irrespective of the type of heat treatment, most of the proteins were found to be present within the mass region of 10-200 kDa and isoelectric point (pI) range from 4 to 9.
The protein fractions that showed significant variations were separated by using the technique of electroblotting and electroelution and run on isoelectric focusing (IEF) in second dimension to determine the isoelectric points.
The presence of acidic groups in a sample may also be characterized in terms of the isoelectric point (IEP).
In addition, size, charge, and isoelectric point of proteins of interest are important characteristics for sample preparation.
The isoelectric point (IEP) was carried out by micro-electrophoresis in a Zeta-Meter ZM-77 (Galindo et al.
The phenotypes of different AAT alleles are identified by determining their isoelectric point (IEF) on a thin-layer polyacrylamide gel in a pH gradient of 4-5.