Protein cationic groups, anions combining

Early attention was focused on the maximum amounts of acid and base with which proteins can combine, as indicative of the number of dissociable cationic and anionic groups which they possess. (Actually the terms acidbinding and base-binding as used in the older literature really refer to the binding and rekase of protons.) Later, analysis of the dependence of the extent of dissociation on pH was employed to give not only the numbers but the equilibrium constants of the various types of dissociating groups. Discrepancies between the dissociation constants found and those... 

The most common application of ion binding to stoichiometric investigations has been the use of certain acids, whose anions are tightly bound to protein, to indicate the number of cationic groups. This type of combination often results in precipitation of the complex, which permits direct... 

The almost endless possibilities of mass spectrometry have been increased by yet another hopeful variant SELDI (surface-enhanced laser desorption ionization). SELDI combines protein chips with a UV-MALDl-TOF. The chips are solid aluminum strips coated with cationic or anionic ion exchangers, with hydrophile or hydrophobic molecules. Chips with activated surfaces are also available. These bind proteins covalently via their amino groups and enable you to coat chips with antibodies or receptors as you need them. Every chip has eight coated holes with a diameter of 1 mm. You apply the sample into the holes. Part of the pro-teins/peptides is adsorbed. The remainder is washed off. The adsorbed proteins/peptides are transferred into matrix and can then be analyzed in the mass spectrometer (Figure 7.8). What can SELDI do better than MALDI ... 

It is quite possible that some heavy metal cations, possibly also the UOa ion, attach themselves to a non-ionogenic group of the protein molecule and this combination of amphoion and cation, since it now carries more positive than negative charges, begins to behave as a colloid cation with respect to the anion and then really forms a dicomplex system with it. 

A second type of isotherm is obtained where there are a definite number of sites within the fibre which can enter into combination with the dye, Na D, the state of affairs which exists with the protein fibres. If it is assumed that the cations present in solution are independently adsorbed by the carboxyl groups, and the anions by the amino groups, then... 

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