A novel derivative of the prosthetic group heme d1: S-methylporphyrindione d1

Several derivatives of heme d1 have been characterized by ultraviolet-visible, NMR, and mass spectrometry. Most arise from side reactions during the isolation of d1 from the enzyme. One, however, has now been shown to correspond to the replacement of a meso proton by an S-methyl group. Since the porphyrin is not exposed to S-methyl-containing reagents during its isolation, this raises hypotheses that it has its origin in vivo.