Properties and Substrate Specificities of Four Esterases fromAspergillus nigerNRRL 337

Properties and substrate specificities of four esterases (Esterase-I, -II, -III, -IV) from Aspergillus niger were studied. Esterase-I and Esterase-II were found to be markedly stable to heat. When Esterase-I was assayed at 35°C using methylacetylsalicylate as a substrate, even after heating at 100°C for 15 min 60% of its activity remained. However, Esterase-I scarcely hydrolyzed the substrate at 70°C or over, because of a reversible change in conformation by heating as found by CD measurement. The maximum activity of Esterase-I was found at 55°C at 20 min of reaction time. Esterase-II was stable up to 80°C and had an optimum temperature for reaction at 80°C, but was irreversively inactivated by heating for 15 min at 90°C. The four esterases hydrolyzed aliphatic esters of short chain fatty acids and acetyl esters of phenols, but neither methyl esters of aromatic carboxylic acids nor acetyl esters of aromatic alcohols.