Isoelectric point table

Each type of mineral or other solid substance has its own isoelectric point or range of isoelectric points (Table 2.11). For compounds that have highly variable compositions (e.g. ferrihydrites in Table 2.11 and Chapter 3), isoelectric points differ with individual specimens. ZPCs will also vary with the electrolyte composition of the aqueous solution (Faure, 1998), 219. 

Like the individual amino acids, proteins are least soluble at their (average) isoelectric points. This means that soluble or dispersed proteins may precipitate or aggregate when the pH of their environment becomes equal to that of the isoelectric point (Table 10.9). 

The surface potential of the reservoir bulk matrix materials cited above depends upon pH of the water phase in contact with the mineral. The pH for which the Zeta potential on a surface is zero is the isoelectric point. These surfaces are positively charged at pH less than the isoelectric point and negatively charged at pH greater than the isoelectric point. Table 2 contains isoelectric points for the common reservoir materials assembled by Maini et al. [54]. Ionic surfactants therefore can be attracted or repulsed from a surface depending upon pH. 

Before leaving this section, it is important to point out that each of the amino acids just discussed has a pK value and an isoelectric point. Table 27.2 shows the name of the amino acid, pK, pK2, the isoelectric point, and pKg, which is only observed when there is an acidic side chain or an amine group on the side chain that can form an ammonium salt. ... 

Table 27 2 includes a column labeled pi which is the isoelectric point of the ammo acid The isoelectric point, also called the isoionic point, is the pH at which the ammo acid has no net charge It is the pH at which the concentration of the zwitterion is a maximum At a pH lower than pi the ammo acid is positively charged at a pH higher than pi the ammo acid is negatively charged For the ammo acids m Table 27 2 pi is the average of pA i and pK 2 and lies slightly to the acid side of neutrality... 

Some ammo acids have side chains that bear acidic or basic groups As Table 27 3 indicates these ammo acids are characterized by three values The third pK reflects the nature of the side chain Acidic ammo acids (aspartic and glutamic acid) have acidic side chains basic ammo acids (lysine arginine and histidine) have basic side chains The isoelectric points of the ammo acids m Table 27 3 are midway between the pK values of the zwitterion and its conjugate acid Take two examples aspartic acid and lysine Aspartic acid has an acidic side chain and a pi of 2 77 Lysine has a basic side chain and a pi of 9 74... 

This table lists the and pi (pH at the isoelectric point) values of a-amino acids commonly found in proteins along with their abbreviations. The dissociation constants refer to aqueous solutions at 25°C. 

Table 2. Isoelectric Points of Some Solids in Aqueous Media...

Surfa.ce (Charge. Inorganic particles have a surface charge in water that is a function of both the particle s character and the pH of the water. Each particle has an isoelectric pH value where the negative and positive charges on the surface just neutralize each other. Isoelectric points for some common inorganic particles are shown in Table 1. 

Table 1. Point of Zero Charge (Isoelectric Point) of Selected Inorganic Particles...

The isoelectric points of the amino acids in Table 27.3 are midway between the pK values of the zwitterion and its conjugate acid. Take two exanples aspartic acid and lysine. Aspartic acid has an acidic side chain and a pi of 2.77. Lysine has a basic side chain and a pi of 9.74. 

The isoelectric point of an amino acid depends on its structure, with values for the 20 common amino acids given in Table 26.1. The 15 neutral amino acids have isoelectric points near neutrality, in the pH range 5.0 to 6.5. The two acidic amino acids have isoelectric points at lower pH so that deprotonation of the side-chain -C02H does not occur at their pi, and the three basic amino acids, have isoelectric points at higher pH so that protonation of the side-chain amino group does not occur at their pi. 

Isobutylene, polymerization of, 1207 Isocyanate. Hofmann rearrangement and,933-934 Isoelectric point (pJ), 1024 calculation of, 1024 table of, 1018-1019 lsoleucine, metabolism of, 911 molecular model of, 304 structure and properties of, 1018 Isomer, conformational, 93 Isomerase, 1041-1042 Isomers, 81... 

As mentioned in Table 8.1, amphoteric surfactants contain both an anionic and a cationic group. In acidic media they tend to behave as cationic agents and in alkaline media as anionic agents. Somewhere between these extremes lies what is known as the isoelectric point (not necessarily, or even commonly, at pH 7), at which the anionic and cationic properties are counterbalanced. At this point the molecule is said to be zwitterionic and its surfactant properties and solubility tend to be at their lowest. These products have acquired a degree of importance as auxiliaries in certain ways [20-25], particularly as levelling agents in the application of reactive dyes to wool. 

Table 6.4 Isoelectric points of some common fillers.

Initial screening conditions are suggested in Table 6.1. Multiple pH values are included because mobile-phase pH can significantly affect retention. Major selectivity shifts such as transpositions in elution order are fairly common changes in resolution are much more so.2,14-16 Changes in retention due to pH variation relate to protein hydration. Proteins are minimally charged at their isoelectric points (pis). This means that they carry the minimum of electrostricted hydration water. Both protein surface hydrophobicity and HIC retention should therefore reach their maximum at a protein s pi.6 As pH is either increased or... 

Table 9.2 Migration Time and Isoelectric Point Reproducibility for Human Hemoglobins A and S Analyzed by CIEF...

Most of the E. coli ribosomal proteins are rather basic with high isoelectric points (Kaltschmidt, 1971) and a high content of basic amino acids (Tables I and II). The complete primary structures of all . coli ribosomal proteins have been determined by Wittmann-Liebold and coworkers (see Table III and Appendix). 

Feruloyl esterase activity was first detected in culture filtrates of Strepto-myces olivochromogenes (49), and has thereafter also been reported for some hemicellulolytic fungi (Table III). A partially purified feruloyl esterase from S. commune liberated hardly any ferulic acid without the presence of xylanase (65). Very recently a feruloyl esterase was purified from Aspergillus oryzae (Tenkanen, M. Schuseil, J. Puls, J. Poutanen, K., /. Biotechnol, in press). The enzyme is an acidic monomeric protein having an isoelectric point of 3.6 and a molecular weight of 30 kDa. It has wide substrate specificity, liberating ferulic, p-coumaric, and acetic acids from steam-extracted wheat straw arabinoxylan. 

Enzyme Properties. The two isolated veratryl alcohol oxidases had very similar properties (Table I). The difference in isoelectric points might be accounted for by aspartate content all other amino acid contents except glycine were the same within experimental error (5%). The specific activities (veratryl alcohol as substrate) were significantly different, but both enzymes contained a flavin prosthetic group (25) and converted one molecule of oxygen to one molecule of hydrogen peroxide during alcohol oxidation. 

The culture filtrates of T. reesei contained a large number of both cellulolytic and hemicellulolytic enzymes, which could be partially separated by chromatofocussing (Fig. 1). Of the cellulolytic enzymes, several endoglu-canases and two cellobiohydrolases have already been isolated and characterized (30). Some of the endoglucanases isolated are nonspecific and have xylanase activity (31). The two major xylanase (Xyl) peaks in Figure 1 corresponded to pi-values of above 7.5 and 5.5. When the former enzyme was further purified (24), its isoelectric point was found to be about pi 9 (Table I). Previously, the presence of at least three electrophoretically different xylanases in T. reesei culture filtrates was reported, with the most acidic one shown to have broad substrate specificity (10). This is in agreement with the reported occurrence of three xylanases (pi > 7, pi 5.1, pi... 

The / -xylosidase of T. reesei was a rather large, probably dimeric enzyme and, like most other / -xylosidases, had an acidic pi-value (Table I). A / -xylosidase purified earlier from T. viride with a molecular weight of 101 kDa also had an isoelectric point pi 4.45 (5). In addition to p-nitrophenyl-/ -xylopyranoside and xylo-oligosaccharides, the / -xylosidase of T. reesei also showed activity with p-nitrophenyl-a-arabinofuranoside as substrate, but did not hydrolyze arabinan or release arabinose from arabinoxylan. The purified a-arabinosidase, however, was capable of effecting both the latter hydrolyses (26, Table II). The isoelectric point of the a-arabinosidase of T. reesei was pi 7.5 and its molecular weight 53 kDa (Table I). 

Thus any amphoteric electrolyte may cause similar variations in precipitative power on each side of its isoelectric point. Tii the following table are given the isoelectric points of a few typical amphoteric electrolytes ... 

Table 8.11. Molecular mass, isoelectric point, and absorption coefficient of proteins)... 

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