relative to the standard provided by an unconstrained five-coordinate imidazoleiron ( ii ) porphyrin , the axial separation ( n ( epsilon ) ... p ( mu ) ) in deoxyhemoglobin of the complexed histidine-nitrogen ( n ( epsilon ) ) atom from the mean plane ( p ( mu ) ) of the protoporphyrin is stretched by [ unk ] 0.30 a .
C0032712
porphyrin
C0033733
protoporphyrin