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n. a molecular species that contains four reduced pyrrole rings joined in a macrocycle by three -CH= groups and one direct bond; central to the cobalt containing vitamin cobalamin

"The interatomic distances in the inner ring of factor VIa, which has been called the corrin ring, conform very closely with the distances proposed 12 for a structure containing six resonating double bonds, so closely as to leave almost no doubt of the correct formulation of its chemical structure (cf.Fig. 9)."

porphyrin   

Orin    florin    laurin    morin