Inhibition of the Trichoderma viride cellulase complex by leaf litter extracts

Abstract

The inhibition of the Trichoderma viride cellulase complex by extracts (hot water and 0.1 N NaOH) of deciduous and coniferous leaf litters in various stages of decomposition was investigated. Endocellulase and exocellulase activities were much more resistant to inhibition than β-glucosidase. White pine extracts were more inhibitory than deciduous ones and deciduous extracts had similar inhibitory potentials regardless of litter type. Except for β-glucosidase inhibition by water extracts, enzyme inhibition declined during decomposition. These results indicate that direct phenolic (humic) inhibition of cellulase components cannot account for species-specific patterns of cellulase activity in decomposing litter or for declining cellulase activity in the late stages of decomposition. Because β-glucosidase, the most readily inhibited component, might potentially limit cellulolysis, it was studied further, β-glucosidase inhibition by litter extracts was mitigated by the action of phenol oxidase and peroxidase. Complexing β-glucosidase with water-soluble litter fractions increased pH optima and Ea values, but did not affect apparent K m . Because of the mitigating effect of oxidative enzymes and presumed differences in extracellular localization of β-glucosidase relative to other cellulase components, β-glucosidase may not limit cellulolysis in situ.