Glutamine deamidation

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. 

Studies of epitope specificity of gliadin antibodies and substrate specificity of tTG point to a role of proline and phenylalanine in amino acid positions +2 and +3 in glutamine deamidation. In contrast, investigations of T-cell stimulatory peptides reveal several potent T-cell stimulatory peptides from the N-terminal part of a-type gliadin containing the PELPY motif. In this connection, it was shown that substitution of phenylalanine in the +3 position or other amino acids in the glutenin peptide Git-156 inhibited the T-cell proliferative response [186]. 

Shutov and Vaintraub [44] reported intensive deamidation activities of protein extracts from germinating seeds. Protein deamidases, prepared and purified from germinating wheat, kidney bean, and squash, were found to be specific to glutamine deamidation, not affected by reducing reagents, and partially inhibited by calcium ions [45]. Relative activity of these enzymes toward a variety of protein substrates were reported (Table 1) [46]. 

Won, J. L, Meagher, R. J., and Barron, A. E. Characterization of glutamine deamidation in a long, repetitive protein polymer via bioconjugate capillary electrophoresis. Biomacwmolecules 5, 618-627 (2004). 

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...

The simplest degradation displayed by asparagine and glutamine is direct hydrolytic deamidation of the side-chain carboxamido group (Fig. 6.29, Pathway d). Such a reaction, however, is seen only at low pH values, and its biological significance appears negligible. Its product is the Asp peptide (6.62) whose further reactions have been presented in Fig. 6.27. 

R. Bischoff, H. V. J. Kolbe, Deamidation of Asparagine and Glutamine Residues in Proteins and Peptides Structural Determinants and Analytical Methodology , J. Chro-matogr., B 1994, 662, 261-278. 

L. Takemoto, D. Boyle, Specific Glutamine and Asparagine Residues of yS-Crystallin Are Resistant to in vivo Deamidation , J. Biol. Chem. 2000, 275, 26109 - 26112 L. Takemoto, D. Boyle, Increased Deamidation of Asparagine During Human Senile Cataractogenesis , Mol. Vision 2000, 6, 164-168. 

Figure 9.5 A summary of pathways of the three main fueb and the positions where they enter the cycle. The figure also shows the release of hydrogen atoms/electrons and their transfer into the electron transfer chain for generation of ATP and formation of water. Glutamine is converted to glutamate by deamidation and glutamate is converted to oxoglutarate by transamination or deamination. The process of glycolysis also generates ATP as shown in the Figure.

A common problem with lenses is cataract, a term that describes any loss of opacity or excessive coloration. There are many kinds of cataract, most of which develop in older persons.560 562 Since lens proteins are so long-lived deamidation of some asparagine occurs. However, the reactions are slow. One of the asparagines in a crystalline has a half-life of 15-20 years, and some glutamines are undamaged after 60 years.575... 

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