Hydroxymethylbilane Synthase Activity Research Articles

Two deletion mutations in the hydroxymethylbilane synthase gene in two unrelated Japanese patients with acute intermittent porphyria.

Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease caused by a decreased activity of hydroxymethylbilane synthase (HMBS). Regarding the abnormalities of the HMBS gene, many different mutations have been reported worldwide; however, few families from Japan have been studied. In this work, we investigated the presence of mutations in two unrelated Japanese patients with AIP. Mutational analysis was performed using the polymerase chain reaction-single strand conformation polymorphism (SSCP) method, followed by DNA sequencing. Reliable restriction enzyme cleavage assays were also established for the pedigree analyses. Unique SSCP patterns were noted in exons 12 and 15 of the HMBS gene. Sequencing revealed different mutations in each patient: a two-base deletion of CT at nucleotide 730-731 (730delCT), and also a two-base deletion of CA at position 982-983 (982delCA). Both of the deletion mutations lead to truncated proteins with an abnormal C-terminus, which would be expected to decrease the stability and/or activity of HMBS. Using the cleavage assays, we were able to definitively identify gene carriers in the family. This study adds a novel mutation to those that have been previously reported, and emphasizes that molecular analysis would be very useful not only for the identification of asymptomatic gene carriers in the family but also for the detection of ancestral founders in porphyria families.

New mutations of the hydroxymethylbilane synthase gene in German patients with acute intermittent porphyria

Acute intermittent porphyria (AIP) is a low-penetrant, autosomal dominant disorder caused by decreased activity of hydroxymethylbilane synthase (HMBS; MIM 176 000), the third enzyme in the heme biosynthetic pathway. We report the first molecular analysis of HMBS gene mutations in classical AIP patients of German origin. The HMBS gene of 5 German AIP patients was analysed by DGGE-screening and direct sequencing of amplified genomic DNA. Five different mutations including four novel mutations were found. Three of them are single base substitutions that affected exon 3 (R16C), exon 10 (V202L), and intron 13 (T to A, IVS13+2) The two remaining mutations are frameshifts which produce a stop codon (del GA in exon 6 and insA in exon 14). These mutations are likely to be responsible for the decrease in HMBS activity found in both erythrocytes and non-erythroid cell lines (lymphocytes). Our results demonstrate the allelic heterogeneity of HMBS mutations in AIP patients of German origin.

Identification and characterization of hydroxymethylbilane synthase mutations causing acute intermittent porphyria: Evidence for an ancestral founder of the common G111R mutation

Acute intermittent porphyria (AIP), the most common hepatic porphyria, results from the half-normal activity of hydroxymethylbilane synthase (HMB-synthase; EC 4.3.1.8), the third enzyme in the heme biosynthetic pathway. Because life-threatening acute neurologic attacks of this autosomal dominant disease are triggered by various ecogenic factors (e.g., certain drugs, hormones, alcohol, and starvation), efforts have been directed to identify and counsel presymptomatic heterozygotes in affected families to avoid the precipitating factors. Thus, to determine the nature of the mutations causing AIP in 26 unrelated enzyme-confirmed patients from Argentina, a long-range polymerase chain reaction method was developed to amplify the entire 10-kb gene in two fragments for efficient cycle sequencing and mutation detection. Eight new mutations were identified including two missense mutations (Q34P and G335S), four small deletions (728delCT, 815delAGGA, 948delA, and 985del12), a single base insertion (666insA), and a splice site mutation (IVS12(+1)). In addition, five previously reported mutations (G111R, R173W, Q204X, R201W, and 913insC) were detected. Notably, G111R was identified in 12 of the 26 (46%) presumably unrelated propositi; however, haplotype analysis with intragenic and flanking markers indicated an ancestral founder. Expression of the two new missense mutations (Q34P and G335S) in f1 E. coli resulted in 2.5% or less of the normal expressed enzyme, confirming their defective function. Thus, eight new and five previously reported HMB-synthase mutations, including a common lesion, were detected, permitting accurate identification and counseling of presymptomatic carriers in these 26 unrelated Argentinean AIP families with this dominant porphyria.

A splicing mutation in the hydroxymethylbilane synthase gene in a Japanese family with acute intermittent porphyria

Objectives: Acute intermittent porphyria (AIP) is an autosomal dominant inherited disease caused by a decreased activity of hydroxymethylbilane synthase (HMBS). As far as the gene abnormalities of the HMBS, many different mutations have been reported. In this work, we investigated the presence of mutations in a Japanese family with AIP. Design and Methods: A 44-year-old Japanese male and nine members of his family were investigated. All of them were screened by traditional biochemical markers. Mutational analysis was performed using polymerase chain reaction-single strand conformation polymorphism method followed by DNA sequencing. A reliable restriction enzyme cleavage assay was established for the pedigree analysis. Results: The mutation was a splicing mutation, a C to G transversion at position −3 of the acceptor site of intron 11 of the HMBS gene, resulting in the exon 12 skipping. The patient is heterozygous for the mutation, and his father appeared to be the source of the mutant allele. This mutation created a new cleavage site of the Nla III restriction enzyme and could be screened by a amplified fragment from genomic DNA with digestion. Using this cleavage assay, an asymptomatic carrier in the family was definitively identified. Conclusions: This mutation was first found among Japanese AIP patients, but happened to be the same as reported previously from Europe. A similarity of gene abnormality may suggest that those European and Japanese AIP families have a common ancestor. Molecular investigations on the family members should be applied not only for more accurate diagnosis, but also for understanding the molecular genetic heterogeniety underlying this dominantly inherited enzymopathy.

Interaction of 5-hydroxymethyl-furfural with hydroxymethylbilane synthase

The inhibition of chlorophyll biosynthesis in greening cress seedlings ( Lepidium sativum L.) by 5-hydroxymethylfurfural (5-HMF), a natural compound isolated from the bulbs of Gladiolus spp. was investigated in vitro and in vivo. A direct reaction between 5-HMF and the chlorophyll precursor porphobilinogen was observed at pH 1.0 but not at pH 8.0. The enzymatic conversion of porphobilinogen to hydroxymethylbilane was inhibited by 5-HMF with a K i of about 30 mM. Enzyme kinetics showed that the inhibition was non-competitive. The activity of hydroxymethylbilane synthase increased during 72 hr development of cress seedlings in darkness. In the light, there was a further increase of enzyme activity. The light dependent increase in activity was completely abolished when the seedlings were incubated with 5-HMF. © 1997 Elsevier Science Ltd. All rights reserved

Acute intermittent porphyria: diagnostic conundrums.

Acute intermittent prophyria is a genetic disorder of haem biosynthesis caused by defects in the gene encoding hydroxymethylbilane synthase on the long arm of chromosome 11. Every effort should be made to identify gene carriers amongst the relatives of patients known to have acute intermittent porphyria as they are at risk of developing potentially fatal neurogenic attacks if exposed to precipitating factors. Erythrocyte hydroxymethylbilane synthase activity was determined in 46 members of two large well characterised families by assaying enzyme activity by both high performance liquid chromatography (HPLC) and fluorimetric assays. Additionally, hydroxymethylbilane synthase immunoreactivity was determined by a sandwich-type ELISA. Statistically significant correlations were observed between erythrocyte hydroxymethylbilane synthase activity assayed by HPLC and by the fluorimetric assay, and enzyme protein concentration (r = 0.85, p < 0.001 and r = 0.80, p < 0.001, respectively). The assay of hydroxymethylbilane synthase immunoreactive concentration in erythrocytes was useful in excluding acute intermittent porphyria in one patient in whom unequivocal assignment of porphyric status was not possible by assaying enzyme activity alone. Erythrocyte hydroxymethylbilane synthase activity assayed by HPLC and fluorimetry showed approximately equal diagnostic performances, both giving rise to a dichotomic distribution of values, with overlap zones of 6% (1/16) and 22% (2/9), respectively, at the "cut off" applied.

Investigation of putative active-site lysine residues in hydroxymethylbilane synthase. Preparation and characterization of mutants in which (a) Lys-55, (b) Lys-59 and (c) both Lys-55 and Lys-59 have been replaced by glutamine

A new construct carrying the hemC gene was transformed into Escherichia coli, resulting in approx. 1000-fold over-expression of hydroxymethylbilane synthase (HMBS). This construct was used to generate HMBS in which (a) Lys-55, (b) Lys-59 and (c) both Lys-55 and Lys-59 were replaced by glutamine (K55Q, K59Q and K55Q-K59Q respectively). All three modified enzymes are chromatographically separable from wild-type enzyme. Kinetic studies showed that the substitution K55Q has little effect whereas K59Q causes a 25-fold decrease in Kapp. cat./Kapp. m. Treatment of K55Q, K59Q and K55Q-K59Q separately with pyridoxal 5'-phosphate and NaBH4 resulted in incomplete and non-specific reaction with the remaining lysine residues. Pyridoxal modification of Lys-59 in the K55Q mutant caused greater enzymic inactivation than similar modification of Lys-55 in K59Q. The results in sum show that, though Lys-55 and Lys-59 may be at or near the active site, neither is indispensable for the catalytic activity of HMBS.

Erythrocyte hydroxymethylbilane synthase activity in a Chinese family with acute intermittent porphyria.

Etude d'une famille chinoise avec analyse de l'activite enzymatique de l'uroporphyrinogen I synthase erythrocytaire et du porphobilinogen urinaire

Characterization of the multiple forms of hydroxymethylbilane synthase from rat spleen.

Phenylhydrazine treatment induced hydroxymethylbilane synthase activity (EC 4.3.1.8) in rat spleen, erythrocytes and liver by 40-fold, 7.5-fold and 6-fold respectively. Five multiple forms of the enzyme were resolved by DEAE-cellulose chromatography. In the presence of phenylmethanesulphonyl fluoride only three forms, two major and one minor, were resolved by the fractionation, suggesting that two of the original forms arose by proteolytic modification. Heat treatment (70 degrees C) in the presence of proteinase inhibitor converted one of the major forms into the other major form. Product isomer analysis suggested that this heat-labile form represented an enzyme-substrate covalent intermediate and not a hydroxymethylbilane synthase-uroporphyrinogen III synthase complex. Identical elution profiles and kinetic properties of the enzymes from rat spleen and erythrocytes suggested that the enzyme isolated from spleen was possibly from stored erythrocytes. Sephadex G-75 chromatography of the heat-stable DEAE-cellulose-purified form yielded pure enzyme as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The Mr was found to be 43000 +/- 1500. Initial-velocity studies on all enzyme forms showed a hyperbolic dependence of velocity on substrate concentration, demonstrating the existence of a displacement-type mechanism. For the heat-stable form Vmax, varied with pH as a typical bell-shaped curve, indicating that two ionizable groups with pK values of 7.4 and 8.8 are important for catalysis. Km decreased with decreasing pH on the acid side of the pH optimum, suggesting the absence of ionization of a group with pK 7.4 in free enzyme or substrate.

Simultaneous determination of hydroxymethylbilane synthase and uroporphyrinogen III synthase in erythrocytes by high-performance liquid chromatography.

A high-performance-liquid-chromatographic method is developed for the simultaneous determination of hydroxymethylbilane synthase and uroporphyrinogen III synthase activity in erythrocytes. Effective separation of uroporphyrin I and III isomers allows the accurate quantification of individual isomers and the total uroporphyrin concentration. Total uroporphyrin production is used to calculate hydroxymethylbilane synthase activity, and the amount of uroporphyrin III formed represents the activity of uroporphyrinogen III synthase. Normal ranges are established for the two enzymes.