7412-77-3Relevant academic research and scientific papers
Revisiting the Mechanism of the Anaerobic Coproporphyrinogen III Oxidase HemN
Ji, Xinjian,Mo, Tianlu,Liu, Wan-Qiu,Ding, Wei,Deng, Zixin,Zhang, Qi
supporting information, p. 6235 - 6238 (2019/04/04)
HemN is a radical S-adenosyl-l-methionine (SAM) enzyme that catalyzes the oxidative decarboxylation of coproporphyrinogen III to produce protoporphyrinogen IX, an intermediate in heme biosynthesis. HemN binds two SAM molecules in the active site, but how these two SAMs are utilized for the sequential decarboxylation of the two propionate groups of coproporphyrinogen III remains largely elusive. Provided here is evidence showing that in HemN catalysis a SAM serves as a hydrogen relay which mediates a radical-based hydrogen transfer from the propionate to the 5′-deoxyadenosyl (dAdo) radical generated from another SAM in the active site. Also observed was an unexpected shunt product resulting from trapping of the SAM-based methylene radical by the vinyl moiety of the mono-decarboxylated intermediate, harderoporphyrinogen. These results suggest a major revision of the HemN mechanism and reveal a new paradigm of the radical-mediated hydrogen transfer in radical SAM enzymology.
Handling heme: The mechanisms underlying the movement of heme within and between cells
Donegan, Rebecca K.,Moore, Courtney M.,Hanna, David A.,Reddi, Amit R.
, p. 88 - 100 (2018/08/21)
Heme is an essential cofactor and signaling molecule required for virtually all aerobic life. However, excess heme is cytotoxic. Therefore, heme must be safely transported and trafficked from the site of synthesis in the mitochondria or uptake at the cell surface, to hemoproteins in most subcellular compartments. While heme synthesis and degradation are relatively well characterized, little is known about how heme is trafficked and transported throughout the cell. Herein, we review eukaryotic heme transport, trafficking, and mobilization, with a focus on factors that regulate bioavailable heme. We also highlight the role of gasotransmitters and small molecules in heme mobilization and bioavailability, and heme trafficking at the host-pathogen interface.
Direct assay of enzymes in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry. Uroporphyrinogen decarboxylase and coproporphyrinogen III oxidase
Wang, Yuesong,Gatti, Paula,Sadilek, Martin,Scott, C. Ronald,Turecek, Frantisek,Gelb, Michael H.
, p. 2599 - 2605 (2008/09/20)
We report new assays of enzymes uroporphyrinogen decarboxylase (UROD) and coproporphyrinogen III oxidase (CPO) in the heme biosynthetic pathway. The assays were developed for use in clinical diagnostics of inherited disorders porphyria cutanea tarda and hereditary coproporphyria, respectively. Electrospray ionization tandem mass spectrometry is used to monitor the decarboxylation of pentaporphyrinogen I or uroporphyrinogen III catalyzed by UROD and to determine the enzyme activity in human erythrocytes by measuring the production of coproporphyrinogen I or III. The Km value for pentaporphyrinogen I was measured as 0.17 ± 0.03 μM. A mass spectrometric assay was also developed for the two-step decarboxylative oxidation of coproporphyrinogen III to protoporphyrinogen IX catalyzed by CPO in mitochondria from human lymphocytes (Km = 0.066 ± 0.009 μM). The assays show good reproducibility, use simple workup by liquid-liquid extraction of enzymatic products, and employ commercially available substrates and internal standards.
Metabolism of pentacarboxylate porphyrinogens by highly purified human coproporphyrinogen oxidase: Further evidence for the existence of an abnormal pathway for heme biosynthesis
Cooper, Christopher L.,Stob, Christian M.,Jones, Marjorie A.,Lash, Timothy D.
, p. 6244 - 6251 (2007/10/03)
An abnormal series of porphyrin tetracarboxylic acids known as the isocoproporphyrins, are commonly excreted by patients suffering from the disease porphyria cutanea tarda (PCT). These porphyrins appear to arise by bacterial degradation of dehydroisocoproporphyrinogen that is generated by the premature metabolism of the normal pentacarboxylate intermediate (5dab) by coproporphyrinogen oxidase (copro'gen oxidase). This porphyrinogen can be further metabolized by uroporphyrinogen decarboxylase to give harderoporphyrinogen, one of the usual intermediates in heme biosynthesis. Therefore, it is possible that some of the heme formed under abnormal conditions may originate from the 'isocopro-type' porphyrinogen intermediate. In order to investigate the feasibility of alternative pathways for heme biosynthesis, the four type III pentacarboxylate isomeric porphyrinogens were incubated with purified, cloned human copro'gen oxidase at 37°C with various substrate concentrations under initial velocity conditions. Of the four isomers, only 5dab was a substrate for copro'gen oxidase and this gave dehydroisocoproporphyrin. The structure of the related porphyrin tetramethyl ester was confirmed by proton NMR spectroscopy and mass spectrometry. The Km value for proto'gen-IX formation from copro'gen, an indicator of molecular recognition, was similar to the Km value for monovinyl product formation with 5dab, although copro'gen-III has an approximately twofold higher Kcat value. Although 5dab is a slightly poorer substrate than copro'gen-III, these results support the hypothesis that an abnormal route for heme biosynthesis is possible in humans suffering from PCT or related syndromes such as hexachlorobenzene poisoning.
