Deamidations

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

Disruption of the native structure of a protein can also contribute to chemical instability by accelerating the rates of a variety of degradation routes, including deamidation, hydrolysis, oxidation, disulfide exchange, /1-elimination, and racemization. 

T. Geiger and S. Clarke, Deamidation, isomerization and racemization at asparaginyl and aspartyl residues in peptides, J. Biol. Chem, 262, 785 (1987). 

S. J. Wearne and T. E. Creighton, Effect of protein conformation on rate of deamidation Ribonuclease A, Proteins Struct. Funct. Genet, 5, 8 (1989). 

R. Tyler-Cross and V. Schirch, Effects of amino acid sequence, buffers and ionic strength on the rate and mechanism of deamidation of asparagine residues in small peptides, J. Biol. Chem, 266, 22549 (1991). 

Joshi AB, Sawai M, Kearney WR, et al. Studies on the mechanism of aspartic acid cleavage and glutamine deamidation in the acidic degradation of glucagon. /. Pharm. Sci. 2005 94 1912-1927. 

Figure 6.19 Deamidation of asparagine and glutamine, yielding aspartic acid and glutamic acid respectively. This process can often be minimized by reducing the final product pH to A-5...

Cleland, J.L., Powell, M.F., and Shire, S.J. 1993. The development of stable protein formulations a close look at protein aggregation, deamidation and oxidation. Critical Reviews in Therapeutic Drug Carrier Systems 10(4), 3,01-ill. 

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