Protoporphyrins

About: Protoporphyrins is a research topic. Over the lifetime, 145 publications have been published within this topic receiving 3486 citations.

Labelling in vivo and chirality of griseofulvin-derived N-alkylated protoporphyrins.

Abstract: 1. We have compared the response to griseofulvin of rats and mice and, in mice, the effect of griseofulvin itself with that of two of its analogues. The severity of protoporphyria shows a correlation with the accumulation of both types of N-alkylated porphyrins previously described after treatment with this drug, namely N-methylproptoporphyrin and the N-griseofulvin protoporphyrin adduct. 2. Both N-alkylporphyrins are chiral, are labelled from 5-amino[4-14C]laevulinate, and their liver accumulation can be inhibited by pretreatment with a suicide substrate of cytochrome P-450, which also prevents porphyria. 3. These findings suggest that cytochrome P-450 is involved in the mechanism of griseofulvin-induced protoporphyria by generating N-methylprotoporphyrin. The N-griseofulvin protoporphyrin adduct may also originate from cytochrome P-450, but more work is necessary to elucidate whether it acts as the precursor for N-methylprotoporphyrin.

Stool porphyrins determined by high pressure liquid chromatography and by fractional hydrochloric acid—ether extraction

Abstract: When stool copro- and protoporphyrin were quantitated by spectrophotometry, after fractional hydrochloric acid-ether extraction, up to 30% of the protoporphyrins were recovered in the coproporphyrin extract. In disorders with elevated stool protoporphyrin excretion (e.g. erythropoietic protoporphyria), this method therefore may give falsely elevated coproporphyrin values. When the stool porphyrins were determined by high pressure liquid chromatography there was no carry-over of protoporphyrin to coproporphyrin. The recoveries were 82 and 87%, and the coefficients of variation 5.6 and 3.1% for proto- and coproporphyrin, respectively. Moreover, in specimens containing a more complex mixture of porphyrins, a complete separation of the C2-C8 porphyrins and porphyrin isomers was obtained in a single run. High pressure liquid chromatography should therefore be considered the method of choice to obtain a quantitative profile of stool porphyrins in the routine laboratory.

Anaerobic protoporphyrin biosynthesis does not require incorporation of methyl groups from methionine.

Abstract: It was recently reported (H. Akutsu, J.-S. Park, and S. Sano, J. Am. Chem. Soc. 115:12185-12186, 1993) that in the strict anaerobe Desulfovibrio vulgaris methyl groups from exogenous L-methionine are incorporated specifically into the 1 and 3 positions (Fischer numbering system) on the heme groups of cytochrome c3. It was suggested that under anaerobic conditions, protoporphyrin IX biosynthesis proceeds via a novel pathway that does not involve coproporphyrinogen III as a precursor but instead may use precorrin-2 (1,3-dimethyluroporphyrinogen III), a siroheme and vitamin B12 precursor which is known to be derived from uroporphyrinogen III via methyl transfer from S-adenosyl-L-methionine. We have critically tested this hypothesis by examining the production of protoporphyrin IX-based tetrapyrroles in the presence of exogenous [14C]methyl-L-methionine under anaerobic conditions in a strict anaerobe (Chlorobium vibrioforme) and a facultative anaerobe (Rhodobacter capsulatus). In both organisms, 14C was incorporated into the bacteriochlorophyll precursor, Mg-protoporphyrin IX monomethyl ester. However, most of the label was lost upon base hydrolysis of this compound to yield Mg-protoporphyrin IX. These results indicate that although the administered [14C]methyl-L-methionine was taken up, converted into S-adenosyl-L-methionine, and used for methyl transfer reactions, including methylation of the 6-propionate of Mg-protoporphyrin IX, methyl groups were not transferred to the porphyrin nucleus of Mg-protoporphyrin IX. In other experiments, a cysG strain of Salmonella typhimurium, which cannot synthesize precorrin-2 because the gene encoding the enzyme that catalyzes methylation of uroporphyrinogen III at positions 1 and 3 is disrupted, was capable of heme-dependent anaerobic nitrate respiration and growth on the nonfermentable substrate glycerol, indicating that anaerobic biosynthesis of protoporphyrin IX-based hemes does not require the ability to methylate uroporphyrinogen III. Together, these results indicate that incorporation of L-methionine-deprived methyl groups into porphyrins or their precursors is not generally necessary for the anaerobic biosynthesis of protoporphyrin IX-based tetrapyrroles.

Determination of the structure of an N-substituted protoporphyrin isolated from the livers of griseofulvin-fed mice

Abstract: Feeding mice with griseofulvin, a widely used anti-fungal agent which induces protoporphyria as a side-effect, leads to the formation in the liver of two green pigments which have been shown to be porphyrin adducts. In this work, the major porphyrin adduct isolated from the livers of griseofulvin-fed mice has been characterized structurally using one- and two-dimensional NMR spectroscopy. The adduct was shown to be an N-alkylated protoporphyrin IX in which the whole of griseofulvin (less a hydrogen atom) is attached to a pyrrole ring nitrogen of the porphyrin. It was shown that the drug-to-porphyrin linkage is an an -O-CH2-Npyrrole = linkage, to either the 4- or 6-position of ring a of griseofulvin. In an attempt to identify which pyrrole nitrogen is involved in this linkage, the 1H spectra of the free base and zinc complex of the adduct were compared with the corresponding spectra of the four regioisomers of N-methylprotoporphyrin. These comparisons indicated that the adduct isolated from the livers of griseofulvin-fed mice is either the NC or the ND regioisomer, although a clear distinction between these two could not be made on the available evidence. The mechanism of formation of the adduct and its relation to griseofulvin-induced protoporphyria are discussed.