- Direct assay of enzymes in heme biosynthesis for the detection of porphyrias by tandem mass spectrometry. Uroporphyrinogen decarboxylase and coproporphyrinogen III oxidase
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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.
- Wang, Yuesong,Gatti, Paula,Sadilek, Martin,Scott, C. Ronald,Turecek, Frantisek,Gelb, Michael H.
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- Revisiting the Mechanism of the Anaerobic Coproporphyrinogen III Oxidase HemN
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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.
- Ji, Xinjian,Mo, Tianlu,Liu, Wan-Qiu,Ding, Wei,Deng, Zixin,Zhang, Qi
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- Handling heme: The mechanisms underlying the movement of heme within and between cells
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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.
- Donegan, Rebecca K.,Moore, Courtney M.,Hanna, David A.,Reddi, Amit R.
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- The oxygen-independent coproporphyrinogen III oxidase HemN utilizes harderoporphyrinogen as a reaction intermediate during conversion of coproporphyrinogen III to protoporphyrinogen IX
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During heme biosynthesis the oxygen-independent coproporphyrinogen III oxidase HemN catalyzes the oxidative decarboxylation of the two propionate side chains on rings A and B of coproporphyrinogen III to the corresponding vinyl groups to yield protoporphyrinogen IX. Here, the sequence of the two decarboxylation steps during HemN catalysis was investigated. A reaction intermediate of HemN activity was isolated by HPLC analysis and identified as monovinyltripropionic acid porphyrin by mass spectrometry. This monovinylic reaction intermediate exhibited identical chromatographic behavior during HPLC analysis as harderoporphyrin (3-vinyl-8,13,17-tripropionic acid-2,7,12,18- tetramethylporphyrin). Furthermore, HemN was able to utilize chemically synthesized harderoporphyrinogen as substrate and converted it to protoporphyrinogen IX. These results suggest that during HemN catalysis the propionate side chain of ring A of coproporphyrinogen III is decarboxylated prior to that of ring B. by Walter de Gruyter.
- Rand, Katrin,Noll, Claudia,Schiebel, Hans Martin,Kemken, Dorit,Duelcks, Thomas,Kalesse, Markus,Heinz, Dirk W.,Layer, Gunhild
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experimental part
p. 55 - 63
(2011/11/05)
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- Biosynthesis of Porphyrins and Related Macrocycles. Part 25. Synthesis of Analogues of Coproporphyrinogen-III and Studies of their Interaction with Copropophyrinogen-III Oxidase from Euglena gracilis
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Analogues of coproporphyrinogen-III have been synthesized in which the propionate groups respectively on ring-A and on ring-B are modified either by homologation or esterification.Coproporphyrinogen-III oxidase from Euglena gracilis acts on the analogues which possess normal substituents on ring-A to generate a vinyl group on that ring.The enzyme does not affect the analogues in which the ring-A propionate group has been changed.Conditions have been defined for the MacDonald synthesis of porphyrins which yield products of high isomeric purity.
- Robinson, John A.,McDonald, Edward,Battersby, Alan R.
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p. 1699 - 1710
(2007/10/02)
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