Enzymes repression

When suitable strains to exploit natural substrates are available, their exploitation of cellulolytic substrates in pure culture could be restricted by the end-products of cellulolysis (cellobiose and glucose) repressing enzyme synthesis or inhibition/inactivation of further enzymic activity (Fig. 1). One of the simplest routes to relieve this difficulty was to use non-celluloly tic... 

Baich, A. Vogel, H.J. N-Acetyl-y-glutamokinase and N-acetylglutamic y-semialdehyde dehydrogenase repressible enzymes of arginine synthesis in Escherichia coh. Biochem. Biophys. Res. Commun., 7, 491-496 (1962)... 

Culbertson, M.R., Donahue, T.F., and Henry, S.A., 1976a, Control of inositol biosynthesis in Saccharomyces cerevisiae Properties of a repressible enzyme system in extracts of wild type (.Ino+) cells. J. Bacteriol. 126 232-242. 

Xylanase synthesis on maltose medium was more sensitive to glucose repression when compared to the enzyme synthesis on the xylan medium (Fig. 3a). At 24 h, xylanase production was at the same level in the medium with maltose and maltose plus glucose at 1.0 g/L. However, glucose at 3.0 or 5.0 g/L repressed enzyme production after 24 h of eultivation, leading to a reduction of 55% on specific activity (about 2.30 U/mg dry biomass Fig. 3a). 

Enzyme (E) molecules contain special pockets called active sites. The active site binds the substrate (S) forming an enzyme-substrate (ES) complex. The ES is converted to an enzyme-product (EP), which subsequently dissociates to products (P) and enzymes (E). Enzymes can be highly substrate specific and catalyze only one group of chemical reactions. Depending on the needs of living cells, some enzyme production can be regulated that is, enzymes can be induced or repressed. Enzyme activity can be influenced by a number of factors, including substrate concentration, temperature, pH, and the concentration of end products of a reaction. 

In accordance with the idea of a strongly repressed enzyme, the in vitro activity oiB. subtilis Pdxl is extremely low = 0.018 mm ). A rough estimate based on... 

Q Exogenous regulator molecule, repressing enzyme production... 

I + Slight repression enzyme L-1 feedback-resistant None leu A... 

Enzyme synthesis in vitro supplements genetic analyses by providing information on the map positions of promotors and genes. And above all, the coupled transcription-translation systems have opened new approaches into the regulation of protein synthesis such as the understanding of the control of the lactose operon and of catabolite repression. Enzyme synthesis in vitro... 

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