PRESSURE AND TEMPERATURE CONTROL OF A THERMOPHILIC CARBOXYPEPTIDASE FROM SULFOLOBUS-SOLFATARICUS

The stability and the catalytic activity of a carboxypeptidase from th e extreme thermophilic archaebacteria S. solfataricus was studied over a wide range of temperature (30-95 degrees C) and pressure (0.1-400 M Pa), and compared to carboxypeptidase A. The thermostability of both c arboxypeptidases could be increased at high pressure. The catalytic ac tivity of the enzyme from S. solfataricus showed two temperature depen dent domains. Below 60 degrees C, the values of the activation energy and activation volume were large: Delta H double dagger = 21 ml/mol, s uggesting a conformation with a high structural rigidity. In the high temperature domain (above 60 degrees C), both terms were quite small ( Delta H double dagger = 9 kJ/mol, Delta V double dagger = 6 ml/mol), c omparable to those of carboxypeptidase A which were always small (Delt a H double dagger = 24 kJ/mol, Delta V double dagger = 0.5 ml/mol), re gardless of the temperature. High pressure appeared to shift the enzym e conformation to the properties of the low temperature domain. These results point to the possibility that the thermostability of carboxype ptidase from S. solfataricus is explained by hydrophobic hydration. Th is enzyme appears to be an interesting model system for the understand ing of the thermo- and barostability of proteases.