The correct structure of heme C was published in mid 20th century by the Swedish biochemist K.-G. Paul. This work confirmed the structure first inferred by the great Swedish biochemist Hugo Theorell.  The structure of heme C, based upon NMR and IR experiments of the reduced Fe(II) form of the heme, was confirmed in 1975.  The structure of heme C including the absolute stereochemical configuration about the thioether bonds was first presented for the vertebrate protein, cytochrome c and is now extended to many other heme C containing proteins.