A LARGE COMPRESSIBILITY CHANGE OF PROTEIN-INDUCED BY A SINGLE AMINO-ACID SUBSTITUTION

The adiabatic compressibility <(beta)over bar (s)> was determined, by means of the precise sound velocity and density measurements, for a se ries of single amino acid substituted mutant enzymes of Escherichia co li dihydrofolate reductase (DHFR) and aspartate aminotransferase (AspA T). Interestingly, the <(beta)over bar (s)>,values of both DHFR and As pAT were influenced markedly by the mutations at glycine-121 and valin e-39, respectively, in which the magnitude of the change was proportio nal to the enzyme activity. This result demonstrates that the local ch ange of The primary structure plays an important role in atomic packin g and protein dynamics, which leads to the modified stability and enzy matic function. This is the first report on the compressibility of mut ant proteins.