Sources of Nitrogen Atmospheric N 2 NO 3 - from lightning and rainfall
Haber Process (same Haber as in chemical warfare) Copyright 2013 Pearson Canada Inc High temperature, high pressure, catalyst
Copyright 2013 Pearson Canada Inc Nitrogen-fixing bacteria convert N 2 to ammonia Rhizobium in plant root nodules Azotobacter Klebsiella Some cyanobacteria Enzymes require anaerobic conditions. Root nodules contain leghemoglobin (i.e. legume hemoglobin). Ties up O 2 and passes to respiration.
Nitrogenase Dinitrogenase component (MoFe) reduces N 2 Dinitrogenase reductase component (Fe) rereduces dinitrogenase N 2 + 8H e ATP ⇄ 2NH 3 + H ADP (Requires a lot of energy.)
Copyright 2013 Pearson Canada Inc So how do we use the ammonia?
:Production of Glutamate Glutamate dehydrogenase Reductive amination Usually running backwards in critters due to low [NH 3 ] Copyright 2013 Pearson Canada Inc
Glutamine synthetase Copyright 2013 Pearson Canada Inc Glutamic acid, glutamine, and -ketoglutarate are primary players in moving nitrogens.
Regulation Copyright 2013 Pearson Canada Inc Glutamine is involved in the metabolism of: Aromatic a.a.s Several other a.a.s Purines Pyrimidines Amino sugars Regulated by feedback inhibition Also regulated globally by signal cascades Adenylation of tyrosine blocks active site
Carbamoyl phosphate synthetase Copyright 2013 Pearson Canada Inc Mitochondrial Cytosolic (Bacterial enzyme accepts both substrates) Carbamoyl phosphate can be made from both ammonia and glutamate
Amino acid metabolism Copyright 2013 Pearson Canada Inc Different organisms can make different sets of amino acids. Those we can’t manufacture are essential amino acids in our diet. Lists of essential and non-essential vary.
Amino acid synthesis via transamination You’ve seen this before. -Amino groups of amino acids come by transamination from Glu You can synthesize all amino acids from their -keto conjugates. For the essential amino acids, we can’t produce the - keto acids. Copyright 2013 Pearson Canada Inc
Also play a role in amino acid degradation Above example is part of the degradation path for alanine. Transamination (transfer of the amide NH 2 to - ketoglutarate) yields pyruvate. Pyruvate can be tossed into PDH and the Krebs cycle. Copyright 2013 Pearson Canada Inc
Amino acid oxidases The -amino group is usually removed by transfer to - ketoglutarate to yield glutamate and the -keto acid. Glutamate is then deaminated by glutamate dehydrogenase. There are also amino acid oxidases, using a flavin electron acceptor. Copyright 2013 Pearson Canada Inc
Copyright 2013 Pearson Canada Inc Fates of deaminated amino acids (i.e. fate of the carbons)
Removal of nitrogenous waste Copyright 2013 Pearson Canada Inc Insects, birds, and reptiles primarily excrete uric acid. Desert mammals like kangaroo rats primarily excrete uric acid. Oddly, so do dalmatians. Uric acid is pretty insoluble. In humans, it is the end product of purine catabolism. Overproduction or underexcretion can lead to the formation of uric acid crystals – frequently starting in the gravitationally lowest joints – i.e. the big toe. That condition is gout, which is often extremely painful.
Gout – a surgical example in the left hand Copyright 2013 Pearson Canada Inc
Removal of nitrogenous waste – the urea cycle The universal product of degrading amino acids is ammonia. Ammonia is toxic at not very high concentrations. You have to get rid of it. If you are an aquatic organism, you can just diffuse in into the environment. We convert ammonia to urea. The basic idea: Add the nitrogens to ornithine to (eventually) make arginine. Cleave the guanidino group off arginine to leave you with ornithine and urea. Urinate out the urea. Throw the ornithine back into the cycle.
Copyright 2013 Pearson Canada Inc
Ammonia transport to the liver Urea formation takes place in the liver Waste nitrogen is transported through the blood as Gln or Ala. Reconverted to ammonia in the liver