The degradation of cotton cellulose by the extracellular cellulase of Myrothecium verrucaria. 2. The existence of an ‘exhaustible’ cellulase

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Abstract
The extensive degradation of cotton by cellulolytic microorganisms was imitated by cell-free culture filtrates from M. verrucaria. There was complete loss of strength with little change in degree of polymerization and a large loss of weight. Since the culture filtrate loses its activity towards cotton during attack, it must be repeatedly renewed for extensive degradation to occur. A filtrate that has ceased to attack a particular cotton sample can weaken a fresh sample by about 15%. This limited activity is due to a stable cellulase (B-enzyme) that may be identifiable with the "cellulases" active towards swollen or soluble cellulosic substrates. It is distinct from the labile enzyme (A-enzyme) necessary for extensive degradation of cotton. A-enzyme is adsorbed by cotton and can be desorbed by alkali and by solutions of cellulose derivatives. Cotton on which the organism has grown thus provides a source of cellulase. The production of A-enzyme which requires the presence of fibrous cellulose in the culture medium is increased if carboxymethylcellulose is added.