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... Introduction
Nitrogen: -present in many intracellular metabolites. ...
-Assimilation from inorganic sources requires reduction to ammonia, followed by incorporation into intracellular metabolites. ...
-This review deals with nitrogen assimilation in E. Coli, its regulation, and role of global regulators in the regulation. ... Physiological Context
Nitrogen Sources
?Bacteria assimilate a variety of inorganic nitrogen sources, but E. Coli assimilates only ammonia aerobically. ... There are many sources of N for E. coli, and ammonia is among them. ... Ammonia provides fastest growth rate and therefore it is considered the preferred N source for E. Coli.
Ammonia Assimilation and Intracellular N Donors
?Primary products of ammonia assimilation are glutamate and glutamine which are the major intracellular N donors
? ... Glutamate dehydrogenase (GDH) or glutamine synthetase (GS) assimilates the ammonia in E. Coli. ... E. Coli both have GDH- and GS- dependent pathway, but they are different.
o GS-GOGAT pathway consumes ATP and thus is used in energy-rich environment, and nitrogen-limited environment. ... *Ammonia assimilation by GS-GOGAT pathway accounts for 15% of cell’s ATO requirement.
o GDH pathway is used in energy-limited environment, and presumably nitrogen-rich environment. ... The biosynthetic requirement of each nitrogen-containing metabolite (how much to synthesize) can be calculated from the chemical composition of E. Coli, and they are seldom different. ... Nitrogen Limitation and the Ntr Response
Proteins required for general nitrogen-limited growth. ... Growth in a minimal medium with a single organic nitrogen source is slower than that with ammonia. Such growth affects the expression of about 100 genes, and these changes are referred as Nitrogen-regulated (Ntr) response. ... Elimination of a few metabolic enzymes can prevent the utilization of a variety of nitrogen sources ?they are limited as “Nitrogen-limited? ...
o AsnB, NADE, amidotransferases: AsnA (ammonia dependent asparagines synthetases) AsnB (Glutamine-dependent asparagines synthetases) nadE (NAD in E coli- ammonia dependent) amidotransferases (glutamine-dependent). *Mutants of these enzymes (these enzymes require high concentration of ammonia) are defective in utilization of organic nitrogen sources
Regulation of GS Activity
? ... If GDH assimilates ammonia, then glutamine’s amide provides 25% of nitrogen, and primary function of GS becomes anabolic. ... If GS-GOGAT assimilates ammonia, then glutamine’s amide provides almost 100% of nitrogen and the assimilatory function becomes quantitatively three times more important. ... Function of Ntr regulators in different environment (Refer to Pic 2)
o Function of regulators varies by nitrogen content in environment and transitions states. ... Nitrogen rich environment prevent adenylylation of GS by feedback inhibition.
o Others are similar
o The transition to nitrogen-limited environment has similar process except a few things. ...
o Steady State w/ nitrogen-limited growth has higher concentration of regulators GlnK and NR I.
Approximate Word count = 2151
Approximate Pages = 8.6
(250 words per page double spaced)
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