Viscosimetric Determination of Endocellulase Activity

Abstract

Cellulose is the most common organic polymer on earth. It provides an important carbon source in ecosystems that receive or produce organic matter of vascular plants. Endocellulase is one of the three types of extracellular enzymes that acts synergistically to transform cellulose to its glucose monomers. Its activity can be estimated by recording the viscosity of a standard cellulose solution. Since naturally occurring cellulose is not soluble in water, it is replaced in the assay by water-soluble carboxymethylcellulose. The analysis described in this chapter is started by homogenizing plant litter and separating the extracellular enzymes in the homogenate from particulate organic matter by filtration or centrifugation. The reduction of viscosity is then monitored in vertical glass capillary tubes containing a solution of carboxymethylcellulose and enzymes. The efflux time of the solution in the viscometer is a measure of viscosity and used to calculate standardized enzyme units. Best results are obtained with an automatic viscosity system, which minimizes measurement errors. Endocellulase activity in decomposing leaves and wood from aquatic and soil environments determined by the described approach vary over more than two orders of magnitude, from 25 to 8800 international enzyme units per gram of organic matter.