Intracellular trafficking of porphyrins.

Hemes are porphyrins that play a critical role in diverse biological processes. Heme synthesis culminates in the mitochondrial matrix, but the eight-step biosynthetic pathway is spatially shared between the mitochondria and cytoplasm. A recent paper describes the nature of the transporter that translocates the heme precursor coproporphyrinogen III into the mitochondria for heme synthesis. The identification of ABCB6 (ATP-binding cassette, subfamily B, member 6) and future studies aimed at precisely delineating the mechanism and the physiological nature of its ligand(s) will further enhance our current understanding of the intracellular movement of tetrapyrroles in eukaryotes.