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Deamidation via cyclic imide of asparaginyl peptides: dependence on salts, buffers and organic solvents.

The deamidation reaction of Asn side chain was studied in the presence of the chemicals usually used at high concentration in the purification and crystallization of peptides and proteins. All the experiments were performed on the model peptide Boc-L-Asn-Gly-Gly-NH2. The pathway of the reaction is not affected by the medium used; in all cases it proceeds through a succinimide intermediate giving a mixture of isoaspartyl and aspartyl peptide. However, the rate of the reaction significantly depends on the solvent: the addition of organic solvents to an aqueous solution of the peptide has the general effect of decreasing the reaction rate, which, on the other hand, is strongly enhanced by a high concentration of organic and inorganic buffers. Only a minor influence is exerted by aprotic salts and polyethylene glycol.

Amides↗
PubMedDate not supplied

Deamidation via cyclic imide in asparaginyl peptides.

The deamidation reaction of asparaginyl peptides was studied as a function of the pH and sequence. The deamidation of Boc-Asn-Gly-Gly-NH2 and the hydrolysis of the corresponding aminosuccinyl (Asu) peptide, Boc-Asu-Gly-Gly-NH2, were carried out in the pH ranges 5-10, whereas the deamidation of Boc-Asn-Ala-Gly-NH2, Boc-Asn-Gly-Ala-NH2 and Boc-Asn-Ser-Gly-NH2 was studied at pH 8.9 only. In each case, the conversion of the amide side-chain moiety of the Asn to carboxyl group occurs via a succinimide intermediate (Asu), and its breakdown leads to a normal and an isoaspartyl peptide. The kinetic constants of the Asu formation and the hydrolytic step increase markedly at basic pH. The influence of the side chain of the residue next to Asn is also discussed.

Amides↗