Pressure dependence of thermolysin catalysis

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Abstract
A comparison of the pressure and temperature dependences of the catalytic reaction of thermolysin, a thermostable neutral protease from Bacillus thermoproteolyticus, with those of a non-thermostable neutral protease from B. subtilis revealed a distinct difference in Km values of these enzymes for 3-(2-furyl)acryloyl-blocked dipeptide and tripeptide substrates, but not for kcat. The volume changes for the binding process (.DELTA.V) for these substrates and several competitive inhibitors were -20 to -30 ml mol for thermolysin and nearly 0 ml/mol for the non-thermostable neutral protease. The enthalpy and entropy changes for the binding process were negative for thermolysin, but positive for the latter enzyme. The activation of volumes for the kcat process were 25 -35 ml mol for both proteases, and activation enthalpy and entropy showed no significant difference between the 2 enzymes. The characteristic difference in the pressure and the temperature dependences seen for the binding process is discussed in relation to the thermostability of the proteases.