Enzyme catabolite repression

The screening method based on diameter of halos yielded only five strains with at least 20% more PG than wild t> e. Most attempts to enhance pectinase production have been made in filamentous fiingi, in which enzyme production is regulated by induction and catabolite repression mechanisms [8], By contrast, PG produced by marxianus is constitutive and not subject to catabolite repression [6], Failure to find greatly enhanced secretion levels is consistent with the idea of a constitutive gene that is capable of only modest further induction. PG was found in this study to be already the most prolific secreted protein of K. marxianus. 

Fig. 5.39. The control of enzyme synthesis by catabolite repression. A control region of the lac operon contains the CAP binding site within the promoter region...

In addition to catabolite repression, the cellulase enzymes themselves are subject to end-product inhibition. For example, as glucose accumulates during saccharification, it interacts noncompetively with cellobiase to inhibit further activity of this enzyme (6). Similar inhibition of endoglucanases occurs when cellobiose accumulates in a saccharification reactor (18,19,20). 

A number of selective-screening methodologies have been devised that have allowed isolation of a series of hyperproducing and catabolite repression-resistant mutants of T. reesei. Yields of cellulase of 15 units/ mL under controlled fermentor conditions have been achieved with both Rut-NG14 and Rut-C30. Quantitative reaction of Rut-NG14 enzyme preparation with purified antibodies to cellobiohydrolase shows that in this mutant, the cellobiohydrolase is specifically hyperproduced relative to the rest of the enzymes in the cellulase complex. Rut-C30, which was derived from Rut-NG14, shows resistance to catabolite repression for... 

Once all of the controllable factors are in place, it is critical to select the proper bacterial combination(s) that enables the appropriate rate of biomass growth and enzyme production. For instance, the primary step in trichloroethylene bioremediation is the production of oxygenases, such as toluene dioxygenase (tod). However, oxidation of trichloroethylene generates intermediates that inactivate the tod enzyme and can even be toxic to the cells themselves, i.e., catabolite repression. Thus, the biomass growth rate and... 

MLS1 Malate synthase, enzyme of the glyoxylate cycle, involved in utilization of non-fermentable carbon sources expression is subject to carbon catabolite repression localizes in peroxisomes during growth in oleic acid medium... 

---