1. Nitrogen cycle Chien-Ming Li MD, Ph.D.

2. Nitrogen cycle 1.Nitrogen fixation 2.Ammonification 3.Nitrification 4.Assimilation 5.denitrification

3. 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

4. Ammonification Organic nitrogen in living things decomposed Enzymes 1.Gln synthetase 2.Glu 2-oxoglutarate aminotransferase 3.Glu Dehydrogenase: Important in amino acid catabolism

5. Nitrification Ammonia  nitrite NH4 +  NO2 - Nitrite  nitrate – Soil: bacteria, ex. Nitrobacter – NO 2 -  NO 3 -

6. Denitrification Nitrate  nitrogen NO 3 -  N 2 Bacteria: Pseudomonas, Clostridium Dust to dust, ash to ash! Cycle completed!