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

Kinetic data on the deamidation reaction of Asn(67) in RNase A and of Asn(3 ) 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 o f the deamidation site in the enzyme, have been determined in a wide range of pH and buffer concentrations. The values observed rate constant (k) for the enzyme are markedly than those for the peptides. However, the k depende nce and buffers is similar for all three substrates, indicating a similar r eaction mechanism. The lower k-values for the enzyme have been quantitative ly related to the thermal stability and the three-dimensional structure of the enzyme.