Catabolic metabolism repression

Nearly all of these chemical transformations are catalyzed en-zymically within the plasmalemma (inside the yeast cell-wall), which is the semipermeable membrane that encloses the protoplasm. Many of these enzymes are present in the cells, even under widely differing conditions of their growth, but a number of processes are involved in enzymic regulation and, thus, in the regulation of sugar catabolism. Some enzymes may be synthesized only in response to the presence of the sugar or of a structurally similar compound. Contrariwise, enzyme synthesis may be repressed by an increase in the concentration of ATP or of some other end-product. These enzyme inductions (for a review, see Ref. 5) and repressions (for a review, see Ref. 6) are two important kinds of control in metabolic regulation. 

Cataboirte repression Inhibition of enzyme synthesis by increased concentrations of certain metabolic products. Enzymes subject to Cr. are formed in reponse to metabolic events (utilization of new nutrients by catabolic enzymes, synthesis of secondary products in certain developmental phases of microorganisms). C. r. is probably present in all organisms, although the molecular mechanisms are diverse. Examples of C.r. are glucose repression of catabolic enzymes in . coU and the enzymes of secondary metabolism in microorganisms, e.g. those for the s thesis of penicillin, actinomycin and riboflavin. 

The synthesis of amylase in C. thermohydrosuljuricum 39E (ATCC 33223) was inducible and subject to cataboUc repression (2i). Catabolic repression resistant mutants were isolated which displayed improved starch metabolism features in terms of enhanced rates of growth, ethanol production and starch consumption (33). In chenxrstat cultures, both wUd type and mutant strains produced amylopuUulanase at... 

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