The role of intramolecular nucleophilic catalysis and the effects of self-association on the deamidation of human insulin at low pH.

摘要: The influence of intramolecular catalysis and self-association on the kinetics deamidation at A-21 Asn residue human insulin was explored low pH 35°C. Observed rate constants overall degradation were determined as a function over range 2.0–5.0 total concentration between 2.0–4.0. pH-rate behavior both monomeric associated from 2.0 to 5.0 indicated by unionized carboxyl terminus A chain. Anhydride trapping with aniline 3.0 provided evidence supporting formation cyclic anhydride intermediate in limiting step indicative nucleophilic catalysis. Insulin presence formed two anilide products, Nδ2-phenyl asparagine aspartic acid insulin, expense desamido formation, consistent partitioning common intermediate. Self-associated degraded approximately 2.5 times greater than that monomer 3. However, had negligible or slight stabilizing effect decomposition 4.0. An apparent downward shift pKa 0.75 units upon catalytic constant which increases -COOH acidity are proposed account for these observations.