Effect of the three-dimensional structure on the deamidation reaction of ribonuclease A

Kinetic data on the deamidation reaction of Asn67 in RNase A and of Asn3 in the two peptides Ac-Cys-Lys-Asn-Gly-Gln-Thr-Asn-Cys-NH2 and Ac-Cys(Me)-Lys-Asn-Gly-Gln-Thr-Asn-Cys(Me)-NH2, whose sequences are similar to that of the deamidation site in the enzyme, have been determined in a wide range of pH and buffer concentrations. The values of the observed rate constant (k) for the enzyme are markedly lower than those for the peptides. However, the k dependence on pH and buffers is similar for all three substrates, indicating a similar reaction mechanism. The lower k-values for the enzyme have been quantitatively related to the thermal stability and the three-dimensional structure of the enzyme.