adenosylcobalamin biosynthesis pathway KEGG:map01110 KEGG:map00860 KEGG:map01100 Biosynthesis of adenosylcobalamin (vitamin B12), a modified tetrapyrrole cofactor. Adenosylcobalamin belongs to the same class of compounds as heme, chlorophyll, siroheme, and coenzyme F430. Most prokaryotic organisms as well as animals (including human) and protists have enzyme that require adenosylcobalamin as cofactor, whereas plants and fungi are thought not to use it. It is one of the most structurally complex protein cofactors ans its biosynthesis remains one of the most enigmatic and exigent metabolic pathways in nature, requiring around 30 enzymes. Two distinct yet similar route exist, known as the oxygene-dependent (aerobic route) and oxygen-independent (anaerobic route) pathways. These pathways diverge at precorrin-2 and merge again at adenosylcobyrate. The major difference between these two routes include the timing of cobalt insertion, the requirement for oxygen and the nature of the extruded carbon fragment which is lost during the ring construction process [McGoldrick et al, 2005]. vitamin B12 biosynthesis GO:0009236 PMID:12196148 PMID:16198574 PMID:16866557 UPa:UPA00148 cofactor biosynthesis porphyrin-containing compound biosynthesis