Cellulase induction

E. T. Reese We have found that nearly all cellulolytic organisms, where cellulase is induced, do produce small amounts of constitutive enzyme, very very low levels. Your measurements here indicate similar very low levels of enzymatic activity. Under the conditions that you use I notice that the glucose did not disappear very rapidly. In our work on cellulase induction, we actually try to reduce the rate at which the substrate is consumed. I am wondering whether your conditions, where it is obvious that the organism wasn t very happy with its environment, were actually limiting growth and so stimulating induction ... 

Soluble inducers are valuable in basic studies aimed at elucidating the nature of cellulase induction. As yet we have not found a good method to use them to obtain large quantities of cellulase. For producing cellulase on a large scale, the fungus is grown on cellulose. 

T. reesei also contains a plasma-membrane-bound P-glucosidase of 70 kDa and IP 8.4 [126], which reacts with monoclonal antibodies against the 80 kDa enzyme [47]. This enzyme probably plays a role in the mechanism of cellulase induction [127, 128] however, it may also be an intermediate of the P-glucosidase secretory pathway. 

The induction of this operon responds to the intracellular concentration of cAMP, which is determined by the carbon source available to the cell. When cells are grown on cellobiose or cellulose that do not inhibit adenylate cyclase, cAMP is made in sufficient quantities for induction of cellulase. On the contrary, when cells are grown on glucose or other readily metabolized carbohydrates that do inhibit adenylate cyclase. 

Xylanolytic systems of yeasts and fungi can also be induced by positional isomers of xylobiose. Induction with Xylp-p-(l- 2)-Xyl/7 is analogous to the sophorose induction of cellulase in filamentous fungi (76). Xylp-p-(l- 2)-Xyl/7 and Xylp-p-(l- 3)-Xyl/7 induced xylanase in C. albidus (77), Trichosporon cutaneum (73), A. pullulans (78) and A. terreus (Hrmova, M. et al., Slovak Academy of Sciences, Bratislava, submitted for publication, 1990). In C. albidus the positional isomers behave differently than does xylobiose (77), in that the response of the cells to them was slower but the enzyme yields were higher than in the presence of xylobiose. This in-icated that isomeric xylobioses were not direct inducers. In agreement with this idea, both Xylp-p-(l- 2)-Xylp and Xylp-p-(l- 3)-Xylp were transformed to Xyl/7-p-(l- 4)-Xyl/7, the natural inducer (79). 

These observations are consistent with the conclusion that auxin treatment leads to the synthesis of BS cellulase, which then accumulates in smooth ER vesicles. There is direct evidence that the synthesis occurs in rough ER vesicles (11). Cellulase activity was shown (25) to increase in RNA-rich pea microsomes, provided these were isolated from auxin-treated tissue, when the preparations were incubated with ingredients necessary for carrying out protein synthesis in vitro. Messenger RNA (mRNA) from these microsomes has been translated in a different ribo-somal system and shown to synthesize BS cellulase protein (II). Thus, it is legitimate to use the term "induction to apply to the ability of auxin to evoke the appearance of mRNA for BS cellulase. 

If the pea cellulases are related as an inactive intracellular precursor (BS) to an active wall-bound enzyme (BI), a delay would be expected between the appearance of BS after auxin induction and its secretion as BI. Such a delay has been observed repeatedly in tests of the relative rates of development of the two enzymes following auxin treatment of decapitated or intact tissue (Figure 3). During the first day after treatment, BS cellulase activity increases up to 18-fold over controls, while BI cellulase activity barely changes. By 2 days, although the BS cellulase activity level has increased further, BI cellulase activity surpasses it. The ascendancy of BI continues for several days, i.e., until effects of the hormone subside and levels of both cellulases begin to decline. Similar... 

From a critical study of the metabolism of poly (A) in auxin-treated pea epicotyl, Verma and Maclachlan (73) showed that discreet classes of poly (A) (presumably part of mRNA s) are differentially associated with free and membrane-bound polysomes. The induction of specific mRNA s, the decline in the rate of synthesis of mRNA s, the polysome content per cell, and the formation of cellulase were all related to the membrane-bound polysomes. Although the rate of in vivo enzyme synthesis is... 

The relationship between catabolite repression by glucose and induction of cellulase by sophorose has been studied in T. viride by Nisizawa and co-workers (36, 37). The induction by sophorose (10 M) was competitively repressed by glucose and other metabolites such as pyruvate. Since glucose was an effective repressor when added one hour after the previous addition of actinomycin D, it was concluded that the repression takes place at the translational level. Previous work indicated (26) that the sophorose induction led to the formation of a cellulase component designated FII, which is the source of cellulase II discussed below. In higher plants indoleacetic acid (38) and abscisic acid (39) have been shown to stimulate cellulase production. 

T t has been reported that fungal cellulases are induced enzymes and that cellulose preparations induce cellulolytic activity while easily assimilable carbon sources give the best fungal growth but less production of enzyme activity (9,12, 14). For example, Horton and Keen (10) found that 7.5 X 10"3M D-glucose repressed the synthesis of cellulase to a basal level in Pyrenochaeta terrestris and suggested that cellulase synthesis was regulated by an induction-repression mechanism. 

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