Identification of Tetrapyrrole Compounds Excreted by Rhodobacter sphaeroides and Sources of the Methyl Hydrogens of Bacteriochlorophyll a Biosynthesized by R. sphaeroides, Based on ¹³C-NMR Spectral Analysis of Coproporphyrin III Tetramethyl Ester

Abstract

Red-fluorescent tetrapyrrole compounds excreted by Rhodobacter sphaeroides into the culture broth were concluded to be coproporphyrinogen (Copro'gen) III and uroporphyrinogen (Uro'gen) I, based on the ¹³C-NMR spectral identification of coproporphyrin (Copro) III tetramethyl ester and uroproporphyrin (Uro) I octamethyl ester. The sources of the methyl hydrogens of bacteriochlorophyll a were established by analysis of the ¹³C-NMR spectra of ²H,¹³C-Copro III tetramethyl ester chemically derived from ²H,¹³C-Copro'gen III biosynthesized through the feeding of δ-amino[2-¹³C]levulinic acid (ALA) to R. sphaeroides in medium containing 50% ²H₂O. We confirmed the previous finding that one of the methyl hydrogens was derived from water in the medium during decarboxylation of four acetyl side chains of Uro'gen III to generate Copro'gen III. It was further shown that the other hydrogen atoms, previously reported to be derived from methylene hydrogens at C-2 of ALA, had been exchanged with hydrogen of water in the medium in the biosynthetic pathways leading from ALA to Copro'gen III.