Order of uroporphyrinogen III decarboxylation on incubation of porphobilinogen and uroporphyrinogen III with erythrocyte uroporphyrinogen decarboxylase

Luo, Jinli; Lim, Chang Kee

doi:10.1042/bj2890529

Cited by 59 publications

(34 citation statements)

References 9 publications

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“…The enzyme will use any of the uroporphyrinogen isomers as substrates, but only the III isomer is used for heme production. Under conditions of substrate excess, decarboxylations occur in a random fashion (38). URO-D, a cytosolic 80-kDa homodimer, functions without the need for a cofactor (17,18).…”

Section: Pcr Genotyping At the Uro-d Locusmentioning

confidence: 99%

A mouse model of familial porphyria cutanea tarda

Phillips¹

2000

Proceedings of the National Academy of Sciences

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Section: Pcr Genotyping At the Uro-d Locusmentioning

confidence: 99%

A mouse model of familial porphyria cutanea tarda

Phillips¹

2000

Proceedings of the National Academy of Sciences

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“…1) (3-6). The decarboxylations of these acetate groups proceed in a preferred order (7), to generate the tetramethyl product (8). Subnormal levels of UroD activity are responsible for porphyria cutanea tarda, in which Uro'gen III accumulates and severe clinical consequences ensue.…”

mentioning

confidence: 99%

Uroporphyrinogen decarboxylation as a benchmark for the catalytic proficiency of enzymes

Lewis

Wolfenden

2008

Proc. Natl. Acad. Sci. U.S.A.

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The magnitude of an enzyme's affinity for the altered substrate in the transition state exceeds its affinity for the substrate in the ground state by a factor matching the rate enhancement that the enzyme produces. Particularly remarkable are those enzymes that act as simple protein catalysts, without the assistance of metals or other cofactors. To determine the extent to which one such enzyme, human uroporphyrinogen decarboxylase, enhances the rate of substrate decarboxylation, we examined the rate of spontaneous decarboxylation of pyrrolyl-3-acetate. Extrapolation of first-order rate constants measured at elevated temperatures indicates that this reaction proceeds with a half-life of 2.3 ؋ 10 9 years at 25°C in the absence of enzyme. This enzyme shows no significant homology with orotidine 5-monophosphate decarboxylase (ODCase), another cofactorless enzyme that catalyzes a very slow reaction. It is proposed that, in both cases, a protonated basic residue (Arg-37 in the case of human UroD; Lys-93 in the case of yeast ODCase) furnishes a counterion that helps the scissile carboxylate group of the substrate leave water and enter a relatively nonpolar environment, stabilizes the incipient carbanion generated by the departure of CO2, and supplies the proton that takes its place.decarboxylase ͉ catalysis ͉ porphyrin ͉ coproporphyrinogen ͉ evolution T he catalytic power of an enzyme can be judged from the rate enhancement that it produces. In general, enzymes act on their substrates at somewhat similar rates, with k cat values ranging between 50 and 5,000 s Ϫ1 . However, the rate constants of the same reactions in the absence of a catalyst vary over a range of at least 15 orders of magnitude. And the rate enhancements produced by enzymes vary over a similarly broad range (Ϸ10 15 -fold), indicating the magnitude of the increase in the enzyme's affinity for the substrate as it passes from the ground state to the transition state (1). Particularly remarkable are those cases in which the enzyme acts as a simple protein catalyst, without the assistance of metals or other cofactors. Such a reaction, the decarboxylation of orotidine 5Ј-phosphate, was found earlier to proceed in the absence of enzyme with a half-time of 7.8 ϫ 10 7 years in the absence of enzyme (2).Here, we describe another reaction, involving a very different substrate (uroporphyrinogen, Uro'gen), that proceeds with a half-life of 2.3 ϫ 10 9 years at 25°C in the absence of enzyme. The enzymes catalyzing these reactions act as pure protein catalysts. Their amino acid sequences show no significant homology.In plants and animals, uroporphyrinogen decarboxylase (UroD, EC 4.1.1.37) catalyzes the first committed step in the biosynthesis of heme, chlorophyll, and the cytochromes. The pioneering experiments of Mauzerall and Granick established that during the action of this single enzyme, the acetate group at the 3-position of each of the 4 pyrrole rings of uroporphyrinogen III (Uro'gen III) is converted to a methyl group, yielding coproporphyrinogen III (Fig. 1) (...

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“…The NMR spectrum confirms the presence of two distinct triamide species as illustrated in Figure 7A Figure 6A. The resonance at 108.6 ppm is in the range of reported values for intermediates amidated at carboxylate d but differs from the chemical shift of carboxamide d of the de-tetramide 2 In the text and in the legends to the figures the substrate, product and partially amidated intermediates in the reaction catalyzed by CbiP are designated by the total number of carboxamide groups. Thus, the substrate, adenosyl cobyrinic a,c-diamide, is referred to as the diamide, while the final product, cobyric acid, is referred to as the hexamide.…”

Section: Effect Of Cbip Mutations On the Amidation Ordermentioning

confidence: 55%

“…For the D146A mutant, a third peak is observed with a retention time slightly longer than the original triamide intermediate species. 2 A comparison of the HPLC assays for the wild type, D146N and D146A mutants is shown in Figure 5. The exact masses of the corrinoid intermediates contained in these peaks were measured with a PE Sciex APJ Qstar Pulsar mass spectrometer.…”

mentioning

confidence: 99%

Partial Randomization of the Four Sequential Amidation Reactions Catalyzed by Cobyric Acid Synthetase with a Single Point Mutation

2007

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Cobyric acid synthetase (CbiP) from Salmonella typhimurium catalyzes the glutamine and ATPdependent amidation of carboxylates b, d, e, and g within adenosyl cobyrinic acid a,c-diamide. After each round of catalysis the partially amidated intermediates are released into solution and the four carboxylates are amidated in the sequential order of e, d, b, and g for the wild type enzyme. In the presence of [γ-18 O 4 ]-ATP and adenosyl cobyrinic a,c-diamide the enzyme will catalyze the positional isotope exchange of the βγ-bridge oxygen with the two β-nonbridge oxygens. This results supports the proposal that ATP is used to activate the carboxylate groups via the formation of a phosphorylated intermediate. CbiP catalyzes the hydrolysis of glutamine in the absence of ATP or adenosyl cobyrinic acid a,c-diamide but the rate of glutamine hydrolysis is enhanced by a factor of 60 in the presence of these two substrates together. This result suggests that the formation of the phosphorylated intermediate is coupled to the activation of the site utilized for the hydrolysis of glutamine. However, the rate of glutamine hydrolysis is approximately 2.5 times the rate of ADP formation, indicating that the two active sites are partially uncoupled from one another and that some of the ammonia from glutamine hydrolysis leaks into the bulk solution. The mutation of D146 to either alanine or asparagine results in a protein that is able to catalyze the formation of cobyric acid. However, the strict amidation order observed with the wild type CbiP is partially randomized with carboxylate b being amidated last. With the D146N mutant, the predominant pathway occurs in the sequence d, e, g, and b. It is proposed that this residue enforces the amidation order in the wild type enzyme via charge-charge repulsion between the side chain carboxylate and the carboxylates of the substrate.The biosynthetic pathway for the assembly of vitamin B 12 is rather complex. There are many enzymes in this pathway that catalyze multiple methylation, decarboxylation, or amidation reactions on key reaction intermediates. For example, in the aerobic pathway from Pseudomonas denitrificans S-adenosyl-L-methionine: uroporphyrinogen III methyl transferase (SUMT) catalyzes the methylation of C2 and C7 of uroporphyrinogen III while the fusion protein CobL catalyzes the methylation of C5 and C15 of dihydro-precorrin 6 (1). The corresponding enzymes in the anaerobic pathway from Salmonella typhimurium are CysG and CbiE, respectively (1). Uroporphyrinogen III decarboxylase catalyzes the ordered decarboxylation of the four acetate side chains of the substrate in the heme biosynthetic pathway (2). In addition, CobB and CobQ in the aerobic pathway from P. denitrificans are responsible for the amidation of six different carboxylate groups on the periphery of the corrin † Supported in part by the NIH (R56 DK30343 to FMR and GM77102 to LW) and the Robert A. Welch Foundation (A-840).*To whom correspondence may be addressed. Phone: (979) Based upon amino acid sequence ali...

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Order of uroporphyrinogen III decarboxylation on incubation of porphobilinogen and uroporphyrinogen III with erythrocyte uroporphyrinogen decarboxylase

Cited by 59 publications

References 9 publications

A mouse model of familial porphyria cutanea tarda

A mouse model of familial porphyria cutanea tarda

Uroporphyrinogen decarboxylation as a benchmark for the catalytic proficiency of enzymes

Partial Randomization of the Four Sequential Amidation Reactions Catalyzed by Cobyric Acid Synthetase with a Single Point Mutation

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