HYDROSTATIC-PRESSURE INDUCES CONFORMATIONAL AND CATALYTIC CHANGES ON 2 ALCOHOL DEHYDROGENASES BUT NO OLIGOMERIC DISSOCIATION

A comparison between the pressure effects on the catalysis of Thermoan aerobium brockii alcohol dehydrogenase (TBADH: a thermostable tetramer ic enzyme) and yeast alcohol dehydrogenase (YADH: a mesostable tetrame ric enzyme) revealed a different behaviour. YADH activity is continuou sly inhibited by an increase of pressure, whereas YADH affinity seems less sensitive to pressure. TBADH activity is enhanced by pressure up to 100 MPa. TBADH affinity for alcoholic substrates increases if press ure increases, whereas TBADH affinity for NADP decreases when pressure increases. Hypothesis has been raised concerning the dissociation of oligomeric enzymes under high hydrostatic pressure (< 200 MPa) [1]. Bu t in the case of these two enzymes, unless the oligomers reassociate v ery quickly (< 1 min), the activity inhibition of YADH at all pressure s and TBADH for pressures above 100 MPa is not correlated to subunit d issociation. Hence we suggest that enzymes under pressure encounter a molecular rearrangement which can either have a positive or a negative effect on activity. Finally, we have observed that the catalytic beha viour of alcohol dehydrogenases under pressure is connected to their t hermostability.