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What are inducible and non inducible enzymes

Glucose is known to repress a large number of inducible enzymes inmanydifferent bacteria. Glucose represses the induction of inducibleoperonsby inhibiting the synthesis of cyclic AMP (cAMP), a nucleotidethatis required for the initiation of transcription of a large number ofinducibleenzyme systems including the lac operon.

Synthesis of an inducible enzyme requires

refers to controlling transcription of the mRNA needed for an enzyme's synthesis. In prokaryotic cells, this involves the induction, repression, or enhancement of enzyme synthesis by that can bind to DNA and either induce, block, or enhance the function of , the enzyme required for transcription. The regulatory proteins are often part of either an operon or a regulon. An is a set of genes transcribed as a message that is collectively controlled by a regulatory protein. A is a set of related genes controlled by the same regulatory protein but transcribed as units. Regulatory proteins may function either as repressors, activators, or enhancers.

Synthesis of an inducible enzyme requires?

For the synthesis of an inducible enzyme to occur

N2 - Murine inducible nitric oxide (NO) synthase (iNOS) is catalytically active only in dimeric form. Assembly of its purified subunits into a dimer requires H4B. To understand the structure-activity relationships of human iNOS, we constitutively expressed recombinant human iNOS in NIH 3T3 cells by using a retroviral vector. These cells are deficient in de novo H4B biosynthesis and the role of H4B in the expression and assembly of active iNOS in an intact cell system could be studied. In the absence of added H4B, NO synthesis by the cells was minimal, whereas cells grown with supplemental H4B or the H4B precursor sepiapterin generated NO (74.1 and 63.3 nmol of nitrite per 106 cells per 24 h, respectively). NO synthesis correlated with an increase in intracellular H4B but no increase in iNOS protein. Instead, an increased percentage of dimeric iNOS was observed, rising from 20% in cytosols from unsupplemented cells to 66% in H4B-supplemented cell cytosols. In all cases, only dimeric iNnS displayed catalytic activity. Cytosols prepared from H4B- deficient cells exhibited little iNOS activity but acquired activity during a 60- to 120-min incubation with H4B, reaching final activities of 60-72 pmol of citrulline per mg of protein per min. Reconstitution of cytosolic NO synthesis activity was associated with conversion of monomers into dimeric iNnS during the incubation. Thus, human iNOS subunits dimerize to form an active enzyme, and H4B plays a critical role in promoting dimerization in intact cells. This reveals a posttranslational mechanism by which intracellular H4B can regulate iNOS expression.

AB - Murine inducible nitric oxide (NO) synthase (iNOS) is catalytically active only in dimeric form. Assembly of its purified subunits into a dimer requires H4B. To understand the structure-activity relationships of human iNOS, we constitutively expressed recombinant human iNOS in NIH 3T3 cells by using a retroviral vector. These cells are deficient in de novo H4B biosynthesis and the role of H4B in the expression and assembly of active iNOS in an intact cell system could be studied. In the absence of added H4B, NO synthesis by the cells was minimal, whereas cells grown with supplemental H4B or the H4B precursor sepiapterin generated NO (74.1 and 63.3 nmol of nitrite per 106 cells per 24 h, respectively). NO synthesis correlated with an increase in intracellular H4B but no increase in iNOS protein. Instead, an increased percentage of dimeric iNOS was observed, rising from 20% in cytosols from unsupplemented cells to 66% in H4B-supplemented cell cytosols. In all cases, only dimeric iNnS displayed catalytic activity. Cytosols prepared from H4B- deficient cells exhibited little iNOS activity but acquired activity during a 60- to 120-min incubation with H4B, reaching final activities of 60-72 pmol of citrulline per mg of protein per min. Reconstitution of cytosolic NO synthesis activity was associated with conversion of monomers into dimeric iNnS during the incubation. Thus, human iNOS subunits dimerize to form an active enzyme, and H4B plays a critical role in promoting dimerization in intact cells. This reveals a posttranslational mechanism by which intracellular H4B can regulate iNOS expression.

one enzyme but an inducible high ..

Synthesis of Inducible Enzymes in Irradiated Yeast Cells: Inhibition by Ionizing Radiation

The role of cyclic a cAMP is complicated. cAMP is required toactivatean allosteric protein called CAP (catabolite activator protein)which binds to the promoter CAP site and stimulates the binding of RNAppolymerase to the promoter for the initiation of transcription. Thus,toefficiently promote gene transcription of the lac operon, not only mustlactose be present to inactivate the lac repressor, but cAMP must beavailableto bind to CAP which binds to DNA to facilitate transcription. Inthepresence of glucose, adenylate cyclase (AC) activity is blocked. ACis required to synthesize cAMP from ATP. Therefore, if cAMP levels arelow, CAP is inactive and transcription does not occur. Intheabsence of glucose, cAMP levels are high, CAP is activated by cAMP,and transcription occurs (in the presence of lactose).

If lactose is unavailable in the environment for the E. coli to use as an energy source, there is no need to produce the enzymes required for lactose utilization. In the absence of lactose (the inducer) , the bacterium produces an active repressor protein that binds to the operator of the lac operon. This prevents RNA polymerase from binding to the promoter region of the operon located ahead of the operator region and transcribing the lac operon structural genes that enable the bacterium to utilize lactose.

Synthesis of Inducible Enzymes in Irradiated Yeast Cells: Inhibition by ..
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Glucokinase is an inducible enzyme—the amount present ..

Agents capable of inducing the SOS response system are, e.g., UV-radiation, MC, methyl methane sulfonate (MMS), and many other chemicals that disrupt DNA, arrest DNA synthesis, and cell division, and lead to accumulation of single stranded (ss) DNA. The level of RecA protein in bacterial cells (like that of UvrD helicase II) is very high. The RecA protein has a strong tendency to form nucleoprotein filaments on ssDNA, and a much weaker one with broken, double stranded (ds) DNA [, ]. This probably protects DNA against destruction, and is required for every aspect of RecA activity. The assembly of RecA on ssDNA proceeds in the 5'-3' direction at a ratio of 1 molecule RecA per 3 DNA bases, and requires dATP or ATP, but no ATP-ase activity. The disassembly, in contrast, requires hydrolysis of ATP to ADP and proceeds much more slowly than the assembly. RecA assembled on ssDNA acquires a coprotease activity, RecA*, which facilitates the self-cleavage of LexA protein resulting in derepression of SOS-regulated genes. LexA protein has a weak auto-cleavage activity, but its cleavage and derepression of the SOS genes occur only in the presence of the RecA* coprotease.

arginine-inducible enzyme 644948, 644950

Murine inducible nitric oxide (NO) synthase (iNOS) is catalytically active only in dimeric form. Assembly of its purified subunits into a dimer requires H4B. To understand the structure-activity relationships of human iNOS, we constitutively expressed recombinant human iNOS in NIH 3T3 cells by using a retroviral vector. These cells are deficient in de novo H4B biosynthesis and the role of H4B in the expression and assembly of active iNOS in an intact cell system could be studied. In the absence of added H4B, NO synthesis by the cells was minimal, whereas cells grown with supplemental H4B or the H4B precursor sepiapterin generated NO (74.1 and 63.3 nmol of nitrite per 106 cells per 24 h, respectively). NO synthesis correlated with an increase in intracellular H4B but no increase in iNOS protein. Instead, an increased percentage of dimeric iNOS was observed, rising from 20% in cytosols from unsupplemented cells to 66% in H4B-supplemented cell cytosols. In all cases, only dimeric iNnS displayed catalytic activity. Cytosols prepared from H4B- deficient cells exhibited little iNOS activity but acquired activity during a 60- to 120-min incubation with H4B, reaching final activities of 60-72 pmol of citrulline per mg of protein per min. Reconstitution of cytosolic NO synthesis activity was associated with conversion of monomers into dimeric iNnS during the incubation. Thus, human iNOS subunits dimerize to form an active enzyme, and H4B plays a critical role in promoting dimerization in intact cells. This reveals a posttranslational mechanism by which intracellular H4B can regulate iNOS expression.

Protein Synthesis -Translation and Regulation

If lactose is available in the environment for the E. coli to use as an energy source, there is a need to produce the enzymes required for lactose utilization. In the presence of lactose (the inducer), a metabolite of lactose called allolactose (a combination of glucose and galactose). The allolactose binds to the active repressor protein rendering it inactive and no longer able to bind to the operator of the lac operon. This allows RNA polymerase, which binds to the promoter region of the operon located ahead of the operator region, to reach and transcribe the lac operon structural genes that enable the bacterium to utilize lactose. The lacX gene codes for LacX, a betagalactosidase enzyme that splits the disaccharide lactose into glucose and galactose. The lacY gene codes for LacY, a beta-galactoside permease that functions as a symporter to pump lactose into the bacterium. The lacA gene codes for LacA, a transacetylase. Its function in lactose catabolism, if any, is uncertain.

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