Both cyclic AMP and a specific inducer acting in concert are required for the synthesis of many inducible enzymes in E. coli. Little enzyme is made in the absence of either. In contrast to the specific inducers which stimulate the synthesis only of the proteins required for their metabolism, cyclic AMP controls the synthesis of many proteins. Glucose and certain other carbohydrates decrease the differential rate of synthesis of inducible enzymes by lowering cyclic AMP concentrations. In the lac operon, cyclic AMP acts at the promoter site to facilitate initiation of transcription. This action requires another protein, the cyclic AMP receptor protein. The nucleotide stimulates tryptophanase synthesis at a translational level. The action of cyclic AMP in E. coli may serve as a model to understand its action on transcriptional and translational processes in eukaryotes.

http://science.sciencemag.org/content/sci/169/3943/339.full.pdf

Cyclic Adenosine Monophosphate in Bacteria

A. Physiology and metabolic studies . . . . . . . . . . . . . . . . . . . . . . . . . . 393 B. Enzymes, nuclear components , genetic and in fo rmat ion mechanisms . . . . . . . . . . . 399 C. Alcohols, solvents and gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401 D. Organic acids, antibiotics, v i tamins , polysacehaxides and other products . . . . . . . . 401 E. Mixed populat ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 402 F. Cells and tissues of higher organisms . . . . . . . . . . . . . . . . . . . . . . . . 404

/pdf/continuous-cultivation-of-microorganisms-15zawybu62.pdf

Continuous cultivation of microorganisms

Induction and catabolite repression of synthesis of cell wall degrading enzymes by the vascular wilt fungi Verticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici have been studied. In cultures containing inorganic salts and tomato stem cell walls each fungus produced a range of extracellular, polysaccharide degrading enzymes. In V. albo-atrum cultures, the enzymes appeared sequentially over 2 to 9 days in the order endopolygalacturonase (endo-PG), exo-arabinanase, endo-pectin-trans-eliminase (endo-PTE), endoxylanase and cellulase; β- d -galactosidase, galactanase and β- d -glucosidase were also produced. Under similar conditions F. oxysporum produced endo-PG, endo-PTE, arabinanase, β- d -galactosidase, xylanase and cellulase. Synthesis of each enzyme was almost always induced specifically by the sugar or uronic acid unit predominant in the specific polymeric substrate for the enzyme. This became evident only when inducers were supplied at rates which prevented their accumulation in cultures. Exceptionally, cellulase was induced by cellobiose but not glucose, and β-galactosidase a and galactanase were induced both by d -galactose and the structurally related l -arabinase. Synthesis was repressed when inducers were present in slight excess of requirements for growth. Synthesis by V. albo-atrum of endo-PG and endo-PTE increased with inducer supply until inducer began to accumulate, then decreased sharply and was almost completely repressed at supply rates three times the optimal value. Synthesis of exo-arabinanase and β-galactosidase decreased as supply of arabinose increased above the optimum but remained at much higher levels relative to those for endo-PG and endo-PTE. Constitutive synthesis of enzymes by V. albo-atrum was also catabolite repressed but to a lesser degree. The significance of induction and catabolite repression in pathogenesis in vascular wilts is discussed.

Regulation of synthesis of cell wall degrading enzymes by Veticillium albo-atrum and Fusarium oxysporum f. sp. lycopersici☆

The enzyme pattern of Saccharomyces cerevisiae was followed during batch growth and in continuous culture in a synthetic medium limited for glucose under aerobic conditions. Seven enzymes were measured: succinate-cytochrome c oxidoreductase, malate dehydrogenase, nicotinamide adenine dinucleotide-linked glutamate dehydrogenase, malate synthase, isocitrate lyase, aldolase, and nicotinamide adenine dinucleotide phosphate (NADP+)-linked glutamate dehydrogenase. During fermentation of glucose and high growth rate (μ) during the first log phase in batch experiments, the first five enzymes (group I) were repressed, and aldolase and NADP+-linked glutamate dehydrogenase (group II) were derepressed. During growth on the accumulated ethyl alcohol and lower μ, the group I enzymes were preferentially formed and the other two were repressed. A sequence of derepression of the group I enzymes was found during the shift from glucose to ethyl alcohol metabolism, which can be correlated with a strong increase in the percentage of single (nonbudding) cells in the population. A correlation between the state of cells in the budding cycle and enzyme repression and derepression is suggested. In continuous culture, the enzyme pattern was shown to be related to the growth rate. The group I enzymes were repressed at high growth rates, while the group II enzymes were derepressed. Each enzyme exhibits a different dependence. The enzyme pattern is shown to depend on the rate of substrate consumption as well as on the type of metabolism and to be correlated with the budding cycle. The enzyme pattern is considered to be controlled by changes of intracellular catabolic or metabolic conditions inherent in the division cycle.

Elizabeth McFall

Papers

Specific metabolic repression of three induced enzymes in escherichia coli