Radioisotope tracer experiments showed that the porphyrin(卟啉) ring of the heme groups in mammals are made from 8 Gly and 8 succinyl-COA (Glu in plants and bacteria). Deficiency of enzymes leading to heme biosynthesis cause diseases called porphyrias (The degradation of heme yields bilirubin, a linear tetrapyrrole derivative, and the typical pigments found
1. Reduction(fixation)of N, into ammonia(NH3 or NH*) 2. Synthesis of the 20 amino acids 3. Synthesis of other biomolecules from amino acids 4. The de novo pathways for purine and pyrimidinebiosynthesis 5. The salvage pathways for purine and pyrimidine reuse