Nitrogen cycle Chien-Ming Li MD, Ph.D.
Nitrogen cycle 1.Nitrogen fixation 2.Ammonification 3.Nitrification 4.Assimilation 5.denitrification
Nitrogen fixation Biological nitrogen fixation – Symbiosis: Azotobacteraceae and Legume – Nitrogenase, 16 ATPs – N 2 + 8H + + 8e - 2NH 3 + H 2 – Assimilation: NH 3 glutamate Chemical nitrogen fixation: Haber process – N 2 + 3H 2 2NH 3 ∆H = -92kJ/mol Physical nitrogen fixation: lightning
Ammonification Organic nitrogen in living things decomposed Enzymes 1.Gln synthetase 2.Glu 2-oxoglutarate aminotransferase 3.Glu Dehydrogenase: Important in amino acid catabolism
Nitrification Ammonia nitrite NH4 + NO2 - Nitrite nitrate – Soil: bacteria, ex. Nitrobacter – NO 2 - NO 3 -
Denitrification Nitrate nitrogen NO 3 - N 2 Bacteria: Pseudomonas, Clostridium Dust to dust, ash to ash! Cycle completed!