Complex sentence: Heme O differs from the closely related heme A by having a methyl group at ring position 8 instead of the formyl group, the isoprenoid chain at position 2 is the same.
Split into simpler sentences: Heme O differs from the closely related heme A by having a methyl group at ring position 8 instead of the formyl group. The isoprenoid chain at position 2 is the same.