The Terminal Step in Tetrapyrrole Metallation

Tetrapyrroles are organic molecules that contain four five-membered heterocyclic (pyrrole) rings, linked in a cyclic or linear array. Haem, chlorophyll, cobalamin (vitamin B12), siroHaem, and coenzyme F430 belong to a family of prosthetic groups that are characterised by their tetrapyrrole-derived nature and contain a central, 

FIGURE 4.8 The tetrapyrrole biosynthetic pathways. Chelatases selectively insert Fe to form haem, to form chlorophyll, Co to form cobalamine, and, in methane-producing bacteria, Ni to form coenzyme Frso- 

Sirohaem is a tetrahydroporphyrin which has adjacent reduced pyrrole rings and is present in bacterial sulfite and nitrite reductases. 

For more information concerning this unusual type of hehx, see Chapter 377. 

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