Cellulase is any of a group of enzymes, produced mainly by fungi, bacteria, and protozoans, that is able to break down cellulose into smaller molecules, primarily sugars. There are several different kinds of cellulase, which differ in their structure and the way they act, but basically all bring about the hydrolysis of cellulose. In the best-known example of cellulase activity, cellulose is broken down into β-glucose by cellulase produced by symbiotic bacteria in the stomachs of herbivores. The basic mechanism involved is the cleaving of β-glycosidic links the connect the sugar units of cellulase.