title: Oxidation of porphyrinogens by horseradish peroxidase and formation of a green pyrrole pigment.
abstract: When humans or plants are exposed to certain chemicals which interfere with heme biosynthetic enzymes, porphyrinogen intermediates accumulate and are oxidized to cytotoxic porphyrins. Here we have investigated the role of peroxidases in porphyrinogen oxidation. Horseradish peroxidase (HRP) rapidly oxidizes uroporphyrinogen to uroporphyrin and this is inhibited by ascorbic acid. HRP also oxidizes deuteroporphyrinogen (a synthetic porphyrin similar to protoporphyrinogen), but the yield of porphyrin is lower than with uroporphyrinogen as substrate. This low yield is in part due to a rapid, HRP-dependent conversion of deuteroporphyrin (but not uroporphyrin) to a green compound with spectral characteristics of a chlorin with a large peak at 638 nm. This reaction requires addition of a sulfhydryl reductant such as glutathione and is inhibited by ascorbic acid. These findings suggest that cellular peroxidases and ascorbic acid levels may play a role in modifying the phototoxic tetrapyrroles which accumulate in plants and humans after certain environmental exposures.
authors.affiliation: Department of Microbiology, Dartmouth Medical School, Hanover, NH 03755, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Jacobs
authors.forename: N J
authors.initials: NJ
authors.lastname: Jacobs
authors.forename: C B
authors.initials: CB
authors.lastname: Kuhn
authors.forename: N
authors.initials: N
authors.lastname: Gorman
authors.forename: F E
authors.initials: FE
authors.lastname: Dayan
authors.forename: S O
authors.initials: SO
authors.lastname: Duke
authors.forename: J F
authors.initials: JF
authors.lastname: Sinclair
authors.forename: P R
authors.initials: PR
authors.lastname: Sinclair
mesh_terms: D006735:Horseradish Peroxidase / Q000378:metabolism*; D010084:Oxidation-Reduction; D011165:Porphyrinogens / Q000378:metabolism*; D013057:Spectrum Analysis; D013379:Substrate Specificity
chemical_list: D011165:Porphyrinogens; D006735:Horseradish Peroxidase