|Section2= |Section3= }}A corrin's a macrocycle related to the porphyrin ring in hemoglobin, consisting of 4 pyrrole subunits, joined on opposite sides by a C-CH3 methylene link, on one side by a C-H methylene link, and with the two of the pyrroles joined directly. Compared to a porphyrin, it's missing a bridging methylene group between a pair of pyrroles. Also, the pyrrole rings in corrin have fully saturated edge-carbons, that's, two hydrogens attached compared to only one in porphyrins. This… (More on Corrin)