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Unformatted text preview: Lecture 22 Synopsis: Regulation of nitrogen assimilation. Chapters 12 and 18.4 I. Inorganic nitrogen assimilation versus dissimilation. A. NH 4 + . Ammonification (primarily a waste product of deamination of amino acids, essentially unregulated) versus assimilation (biosynthetic incorporation into amino acids, routes subject to some complex regulation by ammonium concentration) versus oxidation (lithotrophic electron donor in nitrifying bacteria, unregulated but sensitive to absence of oxygen). B. NO 3- . Assimilatory nitrate reduction (biosynthetic nitrate reduction to nitrite and thence to ammonium, repressed by ammonium, induced by nitrate, insensitive to oxygen tension) versus dissimilatory nitrate reduction (alternative electron acceptor in respiration, membrane and electron transport associated nitrate reduction to nitrite, insensitive to ammonium, induced by nitrate, repressed by oxygen). C. NO 2- . Assimilatory nitrite reduction (biosynthetic nitrite reduction to ammonium, repressed by ammonium, induced by nitrate/nitrite, insensitive to oxygen tension) versus dissimilatory nitrite reduction (alternative electron acceptor in respiration). There are two routes of dissimilatory nitrite reduction: 1. reduction to ammonium by enterics such as E . coli , (insensitive to ammonium, induced by nitrite, repressed by oxygen; also called nitrite respiration); 2. reduction to nitric oxide, then nitrous oxide and ultimately dinitrogen [N 2 ] in a process called denitrification by various facultative anaerobic, obligate respiratory microorganisms (insensitive to ammonium, induced by nitrite, repressed by oxygen). D. N 2 . Assimilatory dinitrogen reduction to ammonium, also called nitrogen fixation (a strictly biosynthetic process, repressed by ammonium and nitrate, and, in most cases, by oxygen). II. Pathways of ammonium assimilation. A. Known potential enzymatic reactions for incorporation of NH 4 + into organic molecules. 1. Dehydrogenases: alanine, aspartate and glutamate dehydrogenases that aminate, in a reductant dependent mechanism, the respective keto acids, pyruvate, oxalacetate and 2-oxoglutarate (2OG, also called α-ketoglutarate or α KG)....
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- Spring '09
- Ammonium, PII, glutamine synthetase, cellular nitrogen status, PII protein