Ammonia isoelectric points

Yields vary with pH, and for the production of ammonia from glycine (37) and alanine (33) the point of lowest ammonia yield is the isoelectric point of the amino acid. 

Figure 5. Change in pH of the ferrous and ferric solution upon the addition of ammonia at I0°C. The isoelectric point (i.e.p.) of Fe(OH)., is at pH 7.7.

Fig. 4.5.7. An example of medium pressure rapid ion exchange chromatography of 16 mg of a protein mixture (left-hand figure) and of 18 mg of a mixture containing protein fragments (right-hand chromatogram) on 20x0.8 cm columns of CM-Spheron 20-40 /im (37). Buffers A, 0.01 ammonia and acetic acid (pH 7) B, 0.1 M ammonia + acetic acid (pH 7) C, O.S M buffer of the same composition was 1 M in NaCl D, 2 M NaCI. The sequence of protein peaks corresponds to their isoelectric points pi. Cyanogen bromine fragments of human serum albumin CB4 and CB3 contain 31 and 185 amino acids.

In the older literature it has already been mentioned that with a weakly alkaline reaction (dilute ammonia) solutions of protamines or histones — which are basic proteins, that is to say, proteins the isoelectric point of which is )> 7 — mixed with solutions of acid proteins" — which are proteins whose isoelectric point is <( 7 — give precipitates which separate out either as flocculi, or as sticky masses or as liquid oil-like" drops... 

Properties A. a. are amphoteric, since they possess both NH2 and COOH groups, and their solutions are ampholytes. In the solid state and in aqueous solution between pH 4 and 9, they are zwitterions Hj N-CHR-COO" (Fig. .). With a few exceptions, they are highly soluble in water, ammonia and other polar solvents, but barely so in nonpolar and less polar solvents such as ethanol, methanol and aeetone. A. a. with hydrophilic side chains are more soluble in water. The water solublility of an A. a. is lowest at its isoelectric point, because the predominant zwitterionic form decreases the hydrophilicity of the amino and carboxyl groups. 

Table 1 lists the phase and chemical composition, textiue parameters and pH values at the isoelectric point (lEP) of supports. The content of free phases ZnO and MgO was determined by their selective dissolving in the 25% ammonia solution of ammonia chloride (2%). 

With aspartate (Asp, D) in hand, the conversion to asparagine (Asn, N) has been shown to be straightforward. As expressed in US. Patent 5326908, when a slurry of aspartic acid (Asp, D) in methanol (CH3OH) and sulfuric acid (H2SO4) is prepared, the 4-carboxylate (that furthest from the amino group) is preferentially methylated and, without isolation, treatment of the reaction mixture with at least a fivefold excess of ammonia (NH3) produces asparagine (Asn, N). After the removal of excess ammonia, adjustment of the pH to the isoelectric point of the amino add (pi 5.4) yielded a crystalline material (Scheme 12.38). 

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