17-30: Effect of phenol concentration and temperature on purified β-glucosidase and hemicellulases

Phenols are strong inhibitors of microbial enzyme production as well as enzyme activities.  There are a wide range of phenolic monomers and oligomers derived from the plant cell wall that inhibit cellulases and hemicellulases.  We report data for several representative phenols on different purified enzymes, and show the impact of phenols on reducing enzyme activity through the combination of higher incubation temperature and phenol concentration.  Enzymes from Aspergillus niger are more resistant to inhibition and/or deactivation to phenols than enzymes from rumen microorganism and selected bacteria. Tannic acid is the most reactive polyphenol and has an immediate effect on deactivating cellulases, hemicelluloses, and ß-glucosidase from all of the microorganisms tested.  Temperature stable enzymes used in these tests are from Thermotoga maritima, a thermophile that grows at up to 80ºC.  The potency of tannic acids decreases with increasing temperature for T. maritima ß-glucosidase, unlike ferulic acid whose effect increases with increasing temperature.  At 50°C, enzyme deactivation ranges from 10 to about 80% of initial ß-glucosidase activity for 3 to 3000 mg tannic acid/mg protein.  The potency of phenolic inhibitors is temperature dependent, with their mode of action negating the potential beneficial effect of increased rate of cellulose hydrolysis rate as temperature increases.