POLYSACCHARIDES 113 



Crude cellulase preparations from several fungi are alike in that 

 their optimum pH is in the acid range, 4.5 to 5.5 (90, 163, 204); the 

 optimum for the enzyme of Stachybotrys atra is, however, higher, pH 

 6.5-8.0 (230a). Studies on Tricholoma furnosum indicate that the 

 enzyme is formed only by cells in contact with cellulose or lichenin, 

 and that the enzyme in a culture is predominantly extracellular (163). 

 Cellulose is apparently attacked at several points along the chain of 

 glucose residues, inasmuch as in the early stages of attack on cellulose 

 there is a decline in optical density without a corresponding liberation 

 of sugars (162, 163a). Other characteristics of fungal cellulases are 

 summarized by Siu (214). 



For the present, a general statement on the nature of cellulase is 

 not possible. The classical view (183) postulates at least two enzymes, 

 a "cellulase" splitting the long polymeric chain to cellobiose residues, 

 and a cellobiase (/?-glucosidase) splitting the disaccharide to glucose. 

 Although substantial evidence exists for the appearance of cellobiose 

 as an intermediate (119, 159a, 250), the process is probably more 

 complex. Two theories, both based on work with Myrothecium 

 verrncaria, have been proposed recently. The first of these postulates 

 a minimum of three enzymes as required for cellulose hydrolysis (83, 

 91a, 150, 190, 191), with only one of them characteristic of the 

 cellulolytic organisms and the others occurring also in non-cellulolytic 

 fungi. In sharp distinction to this view, other studies on the same 

 organism (251, 253) have resulted in the isolation of an apparently 

 single enzyme, purified to electrophoretic homogeneity, with a molec- 

 ular weight of 63,000. This single enzyme hydrolyzes cellulose to 

 glucose without the obligatory participation of cellobiose as an in- 

 termediate, although cellobiose may be formed during the process. 

 The enzyme acts, at different rates, on cellobiose, cellotriose, and 

 higher oligosaccharides of this group (252), and is inhibited by 

 sulfhydryl reagents (14). It is obvious that further work on the enzyme 

 will be necessary before any general theory can be formulated. 



The Breakdivn of Hemicelluloses and Pentosans. The hemicellu- 

 loses are poorly defined plant constituents, particularly of wood and 

 gums. The principal components of the hemicelluloses are polysac- 

 charides and polyuronides. The literature reports essentially two 

 types of work, that on hemicellulose fractions of unknown composi- 

 tion, and that on more or less purified polysaccharides derived from 

 hemicellulose. 



Crude hemicellulose fractions from wood are attacked by enzymes 

 of Aspergillus oryzae, yielding free sugars and a soluble polysaccharide 



