from The American Heritage® Dictionary of the English Language, 4th Edition
- 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.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. Any of a class of heterocyclic compounds containing four pyrrole rings arranged in a square; they are important in biochemistry in a form with a metal atom in the central cavity (hemoglobin with iron, chlorophyll with magnesium, etc.).
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. any of various pigments distributed widely in living tissues
Greek porphurā, shellfish yielding purple dye, purple + -in.(American Heritage® Dictionary of the English Language, Fourth Edition)