Biosynthetic Origins of the Carbon Skeleton of Heme d1

13C-labeling experiments were performed to determine the simple precursor metabolites that contribute to the tetrapyrrole skeleton of heme d1. By use of 5-[4-13C]aminolevulinic acid it was determined that the skeleton is derived from 8 eq of this acid and that the labeled carbons appeared at sites Cl, C3, C6, C8, C11, C13, C17, and C19 (IUB-IUPAC tetrapyrrole nomenclature). In the course of this study, it was discovered that the glycine-succinyl-coenzyme A pathway to 5-aminolevulinate is not operative in Pseudomonas aeruginosa. 13C chemical shifts are reported for the complete skeleton of the free base porphyrin d1 methyl ester derivative, except for C4 and C9.