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Hemoglobin surface charge

Macromolecules often have a number of sites for interactions and binding of the solute or ligand molecules. For example, hemoglobin in the blood binds oxygen at certain sites. Surface charges on the molecules also affect the diffusion. Therefore, the presence of macromolecules and small solute molecules in solutions may affect Fickian-type diffusion. Most of the experimental data on protein diffusivities have been extrapolated to very dilute or zero concentration since the diffusivity is often a function of concentration. Table 6.4 shows diffusivities of some proteins and small solutes in aqueous solutions. The diffusion coefficients for the macromolecules of proteins are on the order of magnitude of 5 X 10 11 m2/s. For small solute molecules, the diffusivities are around 1 X 10 9 m2/s. Thus, macromolecules diffuse about 20 times slower then small molecules. [Pg.357]

Figure 6. The fraction of oligomeric channels open as a function of the surface charge density (in charges per 100 nm2). The equilibrium constant for the channel-opening reaction is assumed to be equal to that of hemoglobin disaggregation, which is also a function of the charge. Figure 6. The fraction of oligomeric channels open as a function of the surface charge density (in charges per 100 nm2). The equilibrium constant for the channel-opening reaction is assumed to be equal to that of hemoglobin disaggregation, which is also a function of the charge.
Allelic polymorphism in a specific gene can produce nearly identical proteins with primary sequences that differ by one or more amino acids. Primary sequence isoforms can be readily separated by CIEF on the basis of their pi if the amino acid substitution changes the surface charge of the protein. Similarly, enzymatic or nonenzymatic posttranslational chemical modification of ionizable protein functional groups can produce chemically distinct isoforms of the same protein with detectably different surface charge and pi. Analysis of hemoglobin by CIEF is an excellent example of how this technique can be applied for the identification and quantification of a family of related proteins that represent a concise subset of the human proteome. Members of this family include many primary... [Pg.93]

Other substances in addition to the serum proteins that have presented adsorption problems are lysozyme, hemoglobin, pea proteins, phycoeryth-rin, ACTH, some basic materials prepared from tissues, egg white proteins, lactase, and milk proteins. In general, amino acids and small peptides do not present the adsorptive problems encountered with most proteins. The basic peptides of the posterior pituitary showed no detectable adsorption (44,74). Flodin and Tiselius (21) have modified the filter paper by altering the surface charge and this has aided in the elimination of adsorption in specific instances. Other methods, such as soaking the paper in a protein solution to saturate the adsorbing groups, have proved of some aid. It is probable that in the future a special paper will be developed for protein work which overcomes this obstacle. However, at present it remains a serious limitation of the method, particularly for preparative work. [Pg.154]

Surface Charge Determines the Aggregation of Hemoglobin Subunits as Predicted by the Surface Free Energy M. Blank... [Pg.1]

SURFACE CHARGE DETERMINES THE AGGREGATION OF HEMOGLOBIN SUBUNITS AS PREDICTED BY THE SURFACE FREE ENERGY... [Pg.557]

Lesk and Chothia did find, however, that there is a striking preferential conservation of the hydrophobic character of the amino acids at the 59 buried positions, but that no such conservation occurs at positions exposed on the surface of the molecule. With a few exceptions on the surface, hydrophobic residues have replaced hydrophilic ones and vice versa. However, the case of sickle-cell hemoglobin, which is described below, shows that a charge balance must be preserved to avoid hydrophobic patches on the surface. In summary, the evolutionary divergence of these nine globins has been constrained primarily by an almost absolute conservation of the hydro-phobicity of the residues buried in the helix-to-helix and helix-to-heme contacts. [Pg.43]

A number of situations may be visualized. Electron transfer may take place between a pair of redox proteins in solution. Certain reactions in the cytoplasm of the red blood cell fall into this category, such as that between hemoglobin and cytochrome b reductase. These reactions will probably occur by an outer-sphere mechanism, as was described earlier for model reactions between isolated electron-transfer proteins and also between these proteins and simple complexes. Interaction between such proteins probably utilizes specific charged areas on their surfaces. The possibility of inner-sphere reactions may have to be considered in a few cases. [Pg.712]


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