Effect of pH and temperature on the stability of (S)-1-phenylethanol dehydrogenase from Aromatoleum aromaticum.

The stability and inactivation of (S)-1-phenylethanol dehydrogenase (S-PEDH) were investigated over a broad pH range under storage and reactor conditions. The enzyme displayed distinct pH optima depending on the parameter considered, with maximal activity at acidic pH (3.5-5.5), highest operational stability at alkaline pH (8.3-9.0), and maximal thermal stability at near-neutral pH. Ligand-dependent effects were observed, with NADH increasing the melting temperature, while isopropanol and acetophenone caused destabilization and reduced catalytic performance. Thermal inactivation was experimentally shown to follow a biphasic pattern. Combined analysis of enzymatic activity and hydrodynamic radius supports a mechanism in which conformational destabilization precedes aggregate growth; suggesting that aggregation a secondary consequence of the initial inactivation event rather than its primary cause. The results of our study highlight the importance of balancing pH, temperature, and solvent conditions to optimize enzyme performance in biocatalytic applications.