por·phy·rin 
(pôrfə-rĭn)
(pôrfə-rĭn)n.
Any of various organic compounds containing four pyrrole rings, occurring universally in protoplasm, and functioning as a metal-binding cofactor in hemoglobin, chlorophyll, and certain enzymes.
[Greek porphurā, purple dye, purple garment; see PURPLE + -IN.]