An investigation was carried out to evaluate the protective effect of polyhydric alcohols, such as propylene glycol and glycerol on the inactivation of an alkaline protease by sodium dodecyl sulfate (SDS) and H2O2. Addition of polyols increased the stability of a Bacillus clausii I-52 alkaline protease towards not only the thermal-induced, but also the SDS and H2O2-induced inactivation. Among the polyols examined, the best results were obtained with propylene glycol. The half-life of the enzyme was increased by 43- and > 105-fold by the addition of 10% (v/v) propylene glycol to the enzyme preparations containing 5% (w/v) SDS and 5% (v/v) H2O2 at 50 degrees C, respectively. Besides the protection effect of propylene glycol from enzyme inactivation by SDS and H2O2, it also improved the hydrolytic efficiency towards substrate like BSA during the protease reaction containing SDS or H2O2. This result suggests that propylene glycol has a significant potential as a good stabilizer of an alkaline protease preparation, which finds use as an additive in industrial applications, especially, the detergent industry. (c) 2005 Elsevier Inc. All rights reserved.