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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
These observations indicated that proteins of different molecular weights, oligomeric distributions, and isoelectric points all produced similar instrument responses.
Ishino, "Determination of isoelectric point value of 3-mercaptopyruvate sulfurtransferase by isoelectric focusing using ribonuclease A-glutathione mixed disulfides as standards," Analytical Biochemistry, vol.
Moreover, low solubility of therapeutic antibodies is more difficult in formulations and may lead to poor biodistribution, undesirable pharmacokinetics behavior, and immunogenicity [23]; for the same purpose, oligopeptides which were having good water solubility were taken in consideration; moreover, the intrinsic properties of proteins such as size, hydrophobicity, lipophilicity, and isoelectric point play important roles in absorption of antibody [23-28] which favors our findings.
At pH below the isoelectric point, the adsorbent surface was protonated, and an electrostatic repulsion existed between the positively charged surface and Cd(II) ions, resulting in the reduced Cd(II) adsorption.
Marchi G, Guilherme LRG, Chang AC, Curi N, Guerreiro MC (2006) Changes in isoelectric point as affected by anion adsorption on two Brazilian Oxisols.
The quantitative differences encountered were represented by 4 complex groups, namely, protein spots 39-44, 47-52, 63-67, and 210-214, with molecular weight (MW) of 66 kDa with Isoelectric Points (Ip) ranging from 7.18-8.3; 60-58 kDa (pI 4.8-5.6); 59-56 kDa (Ip 5.8-6.4); 14.2 kDa (Ip 5.2-6.2), respectively.
where IPm is the isoelectric point of the mixture of amino acids, IPi is the isoelectric point of the ith amino acid in the mixture and Xi is the mass or mole fraction of the ith amino acid in the mixture.
With IFE, each hemoglobin has a defined isoelectric point (pI) (Table 1).
The pH of solution was adjusted to isoelectric point (PI) of BSA i.e.
Separation of the Hb in this method is related to the isoelectric point of the Hb.
Cation exchange film absorbed [H.sup.+] shows the acidic property, and its pH is lower than isoelectric point (pH 4.35).
Results showed that TEM positive isolates produced beta lactamases consistent with pI (isoelectric point) of 5.4 and 5.6.