Schematic diagram of the porphyrin and heme synthesis pathway

Some of the chemical reactions in this pathway occur in the mitochondria (yellow background) whereas others occur in the cytoplasm (white background). The initial reaction and the terminal 2 reactions are performed in the mitochondria. So δ-aminolevulinic acid formed in the mitochondria must move to the cytoplasm, and then, after a series of chemical intermediaries, coproporphyrinogen formed in the cytoplasm must move into the mitochondria to form protoporphyrinogen III and finally heme. (Figure by William Heric. Courtesy of Wikimedia Commons. Creative Commons Attribution-Share Alike 3.0 Unported license.)