Overview of Nitrogen Metabolism
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- Which prokaryotes can fix atmospheric nitrogen?
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1. free-living soil bacteria (Azotobacter)
2. Nitrogen-fixing bacteria, symbionts of leguminous plants (Rhizobium) - How many ATP and electrons are required for nitrogen fixation?
- 16 ATP; 8 electrons
- Nitrogen is converted to ammonia by the ?.
- Nitrogenase complex.
- In nitrogen fixation, electrons are transferred from ? to ? via ? and ?.
- pyruvate; dinitrogenase; ferredoxin (or flavodoxin); denitrogenase reducatase
- Ammonia is incorporated into biomecules through ? and ?.
- Glutamate and Glutamine
- What is the main regulatory enzyme in nitrogen metabolism?
- Glutamine synthetase
- What serves as allosteric inhibitors of glutamine synthesis?
- alanine, glycine, and 6 end products of glutamine metabolism
- The alternative pathway of glutamate synthesis (minor) is catalyzed by ?
- glutamate dehydrogenase
- Glutamine synthetase is also regulated by what other mechanism?
- covalent modifications
- Adenylation of ? inhibits enzymatic activity of glutamine synthetase.
- Tyr397
- Both adenylation and deadenylation of glutamine synthetase are promoted by which enzyme?
- adenylyltransferase (AT)
- The activity of P(II) is regulated by ?.
- uridylyltransferase (UT)
- The adenylyltransferase complex with uridylylated P(II) stimulates ?.
- deadenylation of glutamine synthetase making it active
- Does uridylylated P (II) increase or decrease transcription of the gene encoding glutamine synthetase?
- Increase.
- How do animals maintain high levels of glutamate?
- By transamination of α-keotglutarate during amino acid metabolism
- What is the prosthetic group of aminotransferases/transaminases?
- Pyridoxal phosphate (PLP)
- Transfer of one carbon groups occurs with either ? or ? as cofactor.
- tetrahydrofolate; S-adenosyl-Methionine
- What are glutamine amidotransferases?
- Enzymes in biosynthetic reactions that use glutamine as a major physiological source of amino group.
- What are the two domains in glutamine amidotransferases?
- The glutamine binding domain (conserved w/ Cys in the active center) and the NH3 acceptor domain (varies).
- What is the covalent intermediate hydrolyzed to?
- Glutamate and the free enzyme
- From where are the carbon skeleon precursors of amino acids derived?
- glycolysis, citric acid cycle, pentose phosphate pathway
- Describe how proline can also be synthesized from ariginine obtained from dietary or tissue protein.
- Arginase, the urea cycle enzyme, converts arginine to ornithine and urea. The ornithine is then converted to glutamate-gammma-semialdehyde by ornithine delta-aminotransferase.
- What enzyme is responsible for removing a carbon atom from serine to generate glycine?
- Serine hydroxymethyltransferase
- What cofactor is required for serine hydroxymethyltransferase?
- tetrahydrofolate, the overall reaction requires PLP also.
- Glycine synthase is required to make glycine from ? and ?.
- CO2 and NH4
- Where in vertebrates can glycine be made?
- In the liver via glycine synthase (from CO2 and NH4)
- How is cysteine generated?
- Methionine furnishes the sulfur atom and serine supplies the carbon skeleton.
- How is homocystein formed?
- From methionine via S-adenosylmethionine and S-adenosylhomocysteine.