Catabolite repression enzyme synthesis

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... 

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...

Lower xylanase production was also observed when B. circulans D1 was cultivated in the medium with glucose. Repression by glucose is common for catabolite extracellular enzymes [14, 41, 42]. However, glucose does not repress xylanase synthesis by some microorganisms [19, 24]. 

Mosbach K, Guilford H, Ohlsson R et al. (1972) General Ugands in affinity chromatography. Cofactor-substrate elution of enzymes bound to the immobilized nucleotides adenosine 5 -monophosphate and nicotinamide-adenine dinucleotide. Biochem J 127(4) 625-631 Moses V, Prevost C (1966) Catabolite repression of P-galactosidase synthesis in Escherichia coli. Biochem J 100(2) 336-353... 

A permease (carrier [16]) is assumed to have the characteristics of an enzyme and thus exhibits stereospecificity for the transported solute. It can traverse the cell membrane, thus transporting the solute from the outside to the inside of the cell, and both influx and efflux of solute occur. The transport will usually exhibit saturation (Michaelis-Menten) kinetics. Enzymes involved in facilitated diffusion or active transport (i.e. permeases and molecules responsible for the intracellular modification of the transported solute) may be either constitutive or inducible. This means that the system may be present at all times (constitutive) or developed by the cell only in the presence of the transported solute (inducible). Clearly for induction to occur some of the solute must enter the cell either by way of a small (constitutive) amount of the transport system or by another means (e.g. diffusion). When the inducer concentration falls to zero or below a critical level, the transport system fails to operate thus a degree of control on the entry of the inducer is exercised. The presence of glucose in the medium may prevent the synthesis of the transport system (catabolite repression) thereby enabling glucose to be... 

Regulation of enzyme amount. Enzyme synthesis is governed by such regulatory mechanisms as induction, repression, and catabolite repression. These mechanisms, which may have drastic effects on cellular composition, have time constants on the order of minutes to hours, and hence result in a much slower adaption than the mechanisms treated before. Drastic... 

A number of publications have appeared on the dynamics of enzyme synthesis in a variety of situations. Most of the models are based on more or less sophisticated versions of the operon model of Jacob and Monod. The role of m-RNA and its stability were modeled by Terui (1972). Repressor and inducer control was treated by Knorre (1968), Imanaka et al. (1972 1973), van Dedem and Moo-Young (1973), and Suga et al. (1975). Allowance for dual control and catabolite repression was made by Toda (1976). [See also the kinetic treatment by Yagil and Yagil (1971), Imanaka and Aiba (1977), and Bajpai and Ghose (1978)]. A simple structured model was developed by Roels (1978) showing a combination of the features of the models published. More recently Toda (1981) reviewed the effects of induction and repression of enzymes in microbial cultures and their modeling. 

Bacteria Escherichia coli Release of glucose inhibition of enzyme induction (see Catabolite repression). Initiation of mRNA synthesis mediated by a specific cAMP receptor protein (catabolite gene activator protein). Inhibition of the degradation of mRNA bound to ribosomes. Stimulation of the synthesis of many enzymes... 

The second class of small molecules exhibiting a regulating effect on enzyme yield are those associated with catabolite repression, of which cyclic AMP is a prime example (see Section 111). Cyclic AMP is usually added to the cell-free system, as its omission results in greatly diminished enzyme activity [24,25], A typical curve showing the dependence of galactosidase activity on cyclic AMP concentration is presented in Fig. 6. Synthesis of transacetylase activity, the product of the third structural gene of the lac operon, is also strongly dependent on the presence of... 

More detailed studies on B. amyloliquefaciens showed that, in this system, extracellular protein accounted for a large proportion of the organism s total protein output (Stormonth and Coleman, 1974). Under favorable conditions the maximum rate of extracellular protein formation was equal to the maximum rate of cell protein synthesis. This observation drew attention to the fact that if exoprotein formation was regulated by catabolite repression then, during exponential growth, if the repressing catabolites were removed, it would not be possible to achieve the maximum rate of extracellular enzyme production without considerable reduction in the growth rate. 

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