Soluble and Particulate Porphobilinogen-Deaminase from Dark-Grown Euglena gracilis

A highly efficient method employing NaSCN as a chaotropic agent was used to dissociate the membrane-bound porphobilinogen-deaminase.

The same sequence of steps was applied for purifying both soluble and membrane dissociated porphobilinogen-deam inase. The chromatographic behaviour of both proteins was quite similar. Euglena gracilis deam inase appears to exist in an equilibrium mixture of two active species of relative molecular masses of 40000 and 20000.

An odd case of heteroallelic acute intermittent porphyria in the Argentinean population

AIP is an acute liver disorder caused by a deficiency of porphobilinogen deaminase (PBGD) characterized by neuroabdominal symptoms. It is an autosomal dominant disease. However, homozygous dominant AIP (HD-AIP) have been described. In some cases erythrodontia was observed. CEP is an autosomal recessive disease produced by mutations in the uroporphyrinogen III synthase gene (UROS), characterized by severe cutaneous lesions and erythrodontia. The aim of the work was to establish the differential diagnosis of porphyria in a patient with abdominal pain, neurological attacks, skin symptoms and erythrodontia. The PBGD activity was reduced 50% and the genetic analysis indicated the presence of two genetic variants in the PBGD gene, p.G111R and p.E258G, a new genetic variant, revealing a case of heteroallelic HD-AIP. The patient, first diagnosed as a carrier of a dual porphyria: AIP / CEP based on the excretion profile of porphyrins, precursors and her clinical symptoms, would be an atypical case of human HD-AIP. These results would also suggest the presence of a phenocopy of the CEP, induced by an endogenous or exogenous factor. Our findings highlight the importance of genetic studies for a proper diagnosis of porphyria, prevention of its manifestation and its treatment.

HFE gene mutations in patients with altered iron metabolism in Argentina

Hereditary Hemochromatosis (HH) is an iron overload syndrome caused by increased duodenal iron absorption, which leads to excessive iron deposition in parenchymal cells of the liver and mayor organs, causing cirrhosis, diabetes, cardiac failure, endocrine complications and arthritis. There are 6 types of HH related to mutations in the genes that encode proteins of iron metabolism. HH Type I is inherited as an autosomal recessive trait of mutations in HFE gene. We investigate the prevalence of C282Y, H63D and S65C mutations in 95 individuals (77 males, 18 females) bearing iron metabolism alterations to establish an early diagnosis of HH. Among this population, 58% carried mutations in the HFE gene (45 males, 10 females). H63D mutation was found in 32.6% of the subjects (29.5% in heterozygocity, 3.15% in homozygocity). S65C mutation was only detected in the heterozygous form (5.3% of the patients), 2 of them carried also H63D mutation. C282Y in heterozygocity was found in 15.8% of the individuals; but only 4.15% carried this mutation in homozygocity. Our findings are in agreement with the prevalence of the Mediterranean origin of most of our patients, where C282Y mutation is not as common as H63D mutation.

The very first description of a patient with hepatoerythropoietic porphyria in Argentina. Biochemical and molecular studies

Hepatoerythropoietic Porphyria (HEP) is the rare homozygous form of Porphyria Cutanea Tarda (PCT). It is characterized clinically by the early onset of severe skin manifestations which can be confused with Congenital Erythropoietic Porphyria (CEP) or with PCT when the symptoms are mild. We describe the case of a 14 year-old child with skin manifestations similar to those observed in PCT. The biochemical assays ruled out a CEP as well as they suggested the development of a HEP. Although his symptoms were not severe enough to be HEP, the enzymatic activity was dramatically reduced to a 5% of normal values and the molecular analysis revealed the presence of two already known different mutations on the patient's URO-D gene, c.703 C>T and IVS9-1. Each parent carry one of the mutations, but they were absent in the brother. This is the first Argentinean HEP case ever described which appeared in a compound heterozygous form and less residual URO-D activity but associated to a mild phenotype.

Acute porphyrias in the Argentinean population: a review

The porphyrias are a group of inherited metabolic disorders of heme biosynthesis which result from a partial deficiency in one of its seven specific enzymes, after its first and rate limiting enzyme, delta-aminolevulinic acid synthetase. They can be classified on the basis of their clinical manifestations into cutaneous, acute and mixed disorders. Acute intermittent porphyria (AIP) is the most common type of hepatic acute porphyrias, inherited as an autosomal dominant trait, caused by a defect in the gene which codifies for the heme enzyme porphobilinogen deaminase. Its prevalence in the Argentinean population is about 1:125,000. A partial deficiency in another enzyme, protoporphyrinogen oxidase, produces variegate porphyria (VP), the second acute porphyria most frequent in the Argentinean population (1:600,000). Here, we review all the mutations we have found in 46 AIP and 9 VP unrelated Argentinean patients. To screen for mutations in symptomatic patients, we have proposed a geneticresearch strategy.

Identification and characterization of two novel mutations that produce acute intermittent porphyria: A 3-base deletion (841-843delGGA) and a missense mutation (T35M)

A partial deficiency of Porphobilinogen deaminase (PBGD) is responsible for acute intermittent porphyria (AIP). AIP is inherited in an autosomal dominant fashion, and the prevalence in the Argentinean population is about 1:125,000. Here, two new mutations and two previously reported were found in the PBGD gene in 22 Argentinean AIP patients corresponding to 8 different families. To screen for AIP mutations in symptomatic patients, genomic DNA isolated was amplified in 6 PCR reactions, then all coding exons and flanking intronic regions were sequenced. The novel mutations are 841-843delGGA in exon 14, which results in the loss of glycine-281 (G281del), and one 104C>T point mutation in the exon 4 (T35M). To further characterize both novel mutations, the pKK-PBGD construct for the mutant alleles were expressed in E. coli, the enzymatic activity of the recombinant proteins were 1% and 4% of the mean level expressed by the normal allele for 841-843delGGA and T35M, respectively. Hum Mutat 16:373, 2000.

Mutations in familial porphyria cutanea tarda: two novel and two previously described for hepatoerythropoietic porphyria

Uroporphyrinogen decarboxylase (URO-D) deficiency is responsible for two forms of genetic cutaneous porphyria: familial porphyria cutanea tarda (f-PCT) and hepatoerythropoietic porphyria (HEP). The f-PCT transmitted as an autosomal dominant trait, is characterized by photosensitive cutaneous lesions frequently associated to hepatic dysfunction and is precipitated by various ecogenic factors. The HEP, transmitted as a recessive trait, is more severe than f-PCT and would be considered as the homozygous form of f-PCT. For the mutational analysis of f-PCT patients, the entire URO-D gene was amplified and each exon, intron-exon boundaries and the promoter region were cycle sequenced. Five mutations were found in 6 unrelated families studied, of these, two were new: a nonsense mutation in exon 6 (W159X) and a splice defect in intron 9 (IVS9(-1)G-->C). The other two missense mutations, P62L and A80G, had been previously reported in the homozygous state in HEP families. The g10insA, reported in our laboratory, was again identified in other two unrelated families. In addition 3 novel URO-D polymorphisms in non-coding regions were found. The reverse transcription-PCR and sequencing of the splice mutation carrier's RNA did not reveal the presence of an abnormal mRNA, suggesting that no stable transcript from the mutated allele is synthesized. These results increase to 39 the number of mutations identified in the URO-D gene; 4 of them causing both HEP and f-PCT.

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.

Acute intermittent porphyria: characterization of two novel mutations in the porphobilinogen deaminase gene, one amino acid deletion (453-455delAGC) and one splicing aceptor site mutation (IVS8-1G>T)

A partial deficiency of Porphobilinogen deaminase (PBG-D) is responsible for acute intermittent porphyria (AIP). AIP is inherited in an autosomal dominant fashion, and the prevalence in the Argentinean population is about 1:125,000. Here, two new mutations and three previously reported were found in the PBG-D gene in 12 Argentinean AIP patients corresponding to 5 different families. To screen for AIP mutations in symptomatic patients, genomic DNA isolated was amplified in 2 Multiplex PCR reactions, then all coding exons and flanking intronic regions were sequenced. The new mutations are 453-455delAGC in exon 9 which results in the loss of an alanine residue at position 152, and one new point mutation in the splicing aceptor site in the last position of intron 8 (IVS8-1G>T) which leds to a 15 bp deletion because a cryptic site (first AG upstream) is used. Both mutations produce amino acid deletion without frameshift effect. To further characterize the 453-455delAGC mutation, the pKK-PBGD construct for the mutant allele was expressed in E. coli, the enzymatic activity of the recombinant protein was 1.3% of the mean level expressed by the normal allele. Finally, three missense mutations, previously reported, were identified in three unrelated families.

Acute intermittent porphyria: biochemical and clinical analysis in the Argentinean population

Acute intermittent porphyria (AIP) is the most common type of hepatic acute porphyria. In this work, we have analyzed the biochemical data of all Argentinean AIP families studied in the Porphyrins and Porphyrias Research Centre (CIPYP). We have shown that: (i) the prevalence for this population is about 1:125,000; (ii) the disease is more frequent in women than in men (7:3); (iii) about 60% are latent carriers; (iv) 15% of patients with symptomatic AIP died during an acute attack; (v) the most important precipitating factors of acute attacks in our population were the ingestion of therapeutic drugs (25%), anesthetics in surgical interventions (25%) and infections (20%); (vi) the initial symptom in Argentinean AIP individuals is severe abdominal pain (100%), and it is often accompanied by constipation (37%), anorexia (37%) and tachycardia (30%); and (vii) the percentage of recurrence of the acute attacks is high (81%).

Familial porphyria cutanea tarda: characterization of seven novel uroporphyrinogen decarboxylase mutations and frequency of common hemochromatosis alleles

Familial porphyria cutanea tarda (f-PCT) results from the half-normal activity of uroporphyrinogen decarboxylase (URO-D). Heterozygotes for this autosomal dominant trait are predisposed to photosensitive cutaneous lesions by various ecogenic factors, including iron overload and alcohol abuse. The 3.6-kb URO-D gene was completely sequenced, and a long-range PCR method was developed to amplify the entire gene for mutation analysis. Four missense mutations (M165R, L195F, N304K, and R332H), a microinsertion (g10insA), a deletion (g645Delta1053), and a novel exonic splicing defect (E314E) were identified. Expression of the L195F, N304K, and R332H polypeptides revealed significant residual activity, whereas reverse transcription-PCR and sequencing demonstrated that the E314E lesion caused abnormal splicing and exon 9 skipping. Haplotyping indicated that three of the four families with the g10insA mutation were unrelated, indicating that these microinsertions resulted from independent mutational events. Screening of nine f-PCT probands revealed that 44% were heterozygous or homozygous for the common hemochromatosis mutations, which suggests that iron overload may predispose to clinical expression. However, there was no clear correlation between f-PCT disease severity and the URO-D and/or hemochromatosis genotypes. These studies doubled the number of known f-PCT mutations, demonstrated that marked genetic heterogeneity underlies f-PCT, and permitted presymptomatic molecular diagnosis and counseling in these families to enable family members to avoid disease-precipitating factors.

Porphyrin biosynthesis in normal and haem mutants of Saccharomyces cerevisiae. Studies on the inheritance of the HEM R+ phenotype

Heme biosynthesis was studied in the segregants of Saccharomyces cerevisiae (DW10 tetrade 2) from D27 and D27/C6 mating, as a function of the carbon source in the growth medium and the physiological state of the cells. The effects of the HEM R+ gene on the 5-aminolevulinate synthase (ALA-S) and 5-aminolevulinate dehydratase (ALA-D) activities of heme biosynthesis in cells grown on nonfermentable and fermentable carbon sources were compared. Profiles obtained for both strains grown on a fermentable carbon source (glucose) were identical. However, in the presence of a nonfermentable carbon source (ethanol), they behave quite different, as if the mutation could only be expressed under these growth conditions. Moreover, their behavior is similar to that found for the parental strains, indicating that for the mutant its particular behavior might be inheritedly linked to the HEM R+ gene, which in turn affects some regulatory aspects of ALA synthesis explaining its characteristic phenotype.

Zinc aminolevulinic acid dehydratase reactivation index as a tool for diagnosis of lead exposure

The correlation between blood lead level (BLL), delta-aminolevulinate dehydratase (ALA-D) activity, and other common biochemical parameters used to assess a plumbism diagnosis have been carefully analyzed, with the aim of correctly interpreting the data handled in the laboratory. No correlation was observed between BLL and free erythrocyte porphyrins. In the case of ALA-D or Zn-reactivated ALA-D despite the direct correlation with BLL, the curve follows a potential or a logarithmic line, which is not the best to calculate BLL. The so-called Zn-ALA-D-reactivation index (iZn) has been defined as the ratio between the activity of Zn-reactivated ALA-D and the activity of ALA-D. The plot of BLL against the iZn revealed a very good linear relationship which allows an estimate of BLL with reasonable accuracy within a very wide range.

Yeast porphobilinogen deaminase also forms enzyme-pyrrole intermediates

The enzyme porphobilinogen deaminase (PBG deaminase, EC 4.3.1.8) catalyzes the condensation of four molecules of PBG to give the linear tetrapyrrol, hydroxymethylbilane. It has been shown that this enzyme forms stable mono-, di-, tri- and tetrapyrrole-enzyme covalent complexes. When the enzyme, partially purified in the absence or presence of phenylmethylsulfonyl fluoride (PMSF) and preincubated with PBG, was applied on DEAE-cellulose columns, three peaks with PBG deaminase activity were detected. Using Ehrlich's reagent, it was found that the active peaks corresponded to mono-, di- and tri-pyrrylmethane-enzyme complexes. Therefore, the mechanism of action of PBG deaminase from Saccharomyces cerevisiae also involves the sequential addition of four PBG units, leading to the formation of the enzyme-substrate intermediate complexes, as has already been described for the same enzyme from other sources.

The role of ALA-S and ALA-D in regulating porphyrin biosynthesis in a normal and a HEM R+ mutant strain of Saccharomyces cerevisiae

Catabolite repression and derepression on delta-aminolevulinate synthase (ALA-S) and delta-aminolevulinate dehydratase (ALA-D) in a normal yeast strain, D27, and its derived D27/C6 (HEM R+) were investigated. ALA-S and ALA-D activities and intracellular ALA (I-ALA) at different physiological states of the cells were measured. In YPD medium, under conditions of repression and when glucose was exhausted, both strains behaved identically as if the mutation was not expressed. In YPEt medium, however, both ALA-S and ALA-D activities were higher than in YPD, but the I-ALA content and the enzymic activity profiles shown by the two strains were quite different. It appears, therefore, that the mutation causes a deregulation of ALA-S, so that its activity is kept at a high level throughout the cell cycle. This would explain the increased levels of cytochromes present in the mutant. This mutation may affect some regulatory aspect of ALA formation and renders an ALA-S of high activity; moreover, this enzyme species seems to be more stable than in the normal strain.

Studies on uroporphyrinogen biosynthesis in pig liver

Porphobilinogen-deaminase (PBG-D) and PBG-D-isomerase complex (PBG-D-I) from pig liver were isolated and partially purified. Uroporphyrinogen I and III formation was found to be linear with time and protein concentration. Optimal pH was about 7.4 and 7.6-7.8 for PBG-D and PBG-D-I complex, respectively. Some properties of the isolated enzymes were studied. Molecular mass determination gave a value of 40,000 Da for PBG-D and 50,000 Da for the complex. Both enzymes exhibited classical Michaelis-Menten kinetics. Km and Vmax parameters were estimated. The effect of several divalent cations, ammonia and thiol reagents was also investigated. The differential action of some of these chemicals on PBG-D and PBG-D-I system would suggest that PBG-D and isomerase may not be only physically adjacent but actually associated.

Studies on porphobilinogen-deaminase from Saccharomyces cerevisiae

Porphobilinogen-deaminase from Saccharomyces cerevisiae has been isolated and partially purified 80- and 230-fold in the absence or presence of phenylmethylsulphonyl fluoride, respectively. Some properties of the isolated enzyme were studied. Porphyrin formation was linear with time and protein concentration. Optimum pH was about 7.5-7.8. Molecular mass of the protein was 30,000 +/- 3000 Dalton when the enzyme was purified in the presence of phenylmethylsulphonyl fluoride. A less active and unstable 20,000 Da molecular mass species was obtained when purification was performed in the absence of the protease inhibitor. Porphobilinogen-deaminase exhibited classical Michaelis-Menten kinetics. The apparent Km for uroporphyrinogen formation was 19 microM; Vmax was 3.6 nmol uroporphyrin/h and the Hill coefficient was n = 1. Also the action of several reagents on the activity was studied. Protective thiol agents had no effect. Heavy metals inhibited both porphyrin formation and porphobilinogen consumption, but known sulphydryl inactivating chemicals inhibit the former without modifying the latter. Ammonium ions had no effect on the activity while hydroxylamine completely inhibited both porphyrin formation and porphobilinogen consumption.

Different porphobilinogen-deaminase forms in wild and mutant strains of Saccharomyces cerevisiae. A possible correlation with its segregants behaviour

1. Different porphobilinogen-deaminase (PBG-D) enzyme forms were found for D 27 and D 27/C6 (HEM R+) strains of Saccharomyces cerevisiae. 2. PBG-D was partially purified and chromatographed on Sephadex G-100 in either the presence or absence of a protease inhibitor. For D 27 only one active peak was observed while for D 27/C6 strain two active peaks were found. 3. A correlation between this differential behaviour and the presence of HEM R+ gene was looked for employing two segregants of one tetrad from D 27 and D 27/C6 mating.

Saccharomyces cerevisiae porphobilinogenase: some physical and kinetic properties

1. Properties of porphobilinogenase (PBGase), the enzyme complex converting porphobilinogen (PBG) into uroporphyrinogens, were studied in a wild strain, D273-10B and a mutant, B231, of Saccharomyces cerevisiae. 2. A well-defined maximum of enzyme activity was observed for the mutant strain after 20 hr of growth; whilst the activity in the wild strain did not vary significantly during growth. 3. Neither PBG consumption nor uroporphyrinogen formation were modified by the presence of air either in the wild or in the mutant strain. 4. In both the wild and mutant strains uroporphyrinogen formation increased linearly with both protein concentration and incubation time. 5. The addition of a mixture of sodium and magnesium salts to the assay system inhibited the enzyme activity of both strains by 50% without modifying the isomer composition. 6. The same optimum pH (7.4) and mol. wt (50,000 +/- 5000) was found for the enzyme from both strains. 7. The enzyme from both the wild and mutant strains shows Michaelis-Menten kinetics when isolated from cells at either the exponential or the stationary phases of growth. Accumulation of porphyrins and delta-aminolevulinic acid occurring during the exponential phase in the mutant strain, did not modify the kinetics.

[Saccharomyces cerevisiae: porphobilinogenase activity in a wild-type strain and its heme-deficient mutant]

Properties of Porphobilinogenase (PBGase), the enzyme complex converting porphobilinogen (PBG) into uroporphyrinogens, were comparatively studied in a wild strain D273-10B and its mutant B231 of Saccharomyces cerevisiae, Figure 1 shows the growth curves for both strains. The basic pattern of growth was observed but, although S. cerevisiae is a facultative aerobe and was grown on dextrose, a diauxic growth curve was not observed. The beginning of the exponential phase was slightly delayed for the mutant, so, its generation time (G = 3.20 h) was greater than that for the wild strain (G = 1.26 h). Optimum conditions for extracting the enzyme from both strains were found to be sonication at 10 mu for 3 min (Table 1). Table 2 shows the effect of centrifugation at 24,000 xg for 30 min on activity. For both strains the amount of porphyrins formed was the same either in the absence or presence of air. It was found (Figure 2) that urogen formation was linear with protein over a wide range of concentrations and with incubation time up to 2h in agreement with previous results for the enzyme of different sources. Figure 3 shows the effect of pH on PBGase activity. An optimum pH of 7.4 was found for both strains employing sodium phosphate buffer pH 8.0. The shape of the pH curve as well as optimum pH were the same in both Tris-HCl and phosphate buffer, however PBGase was 15% less active in the former. When plots of velocity against PBG concentration were analyzed for PBGase, it was found that measuring the rate of the reaction on the basis of total urogen formation, saturation curves for wild and mutant strains harvested at the exponential phase, followed classical Michaelis-Menten kinetics. Saturation was reached at PBG concentration of about 70-90 microM. Therefore, double reciprocal plots (Figure 4) were linear and from these plots apparent Km's values of 20 and 14 microM were obtained for the wild and mutant strain respectively. It is known that in some organisms, the activity of the enzyme of heme synthesis is significantly influenced by the days of growing; therefore the effect of time growing on PBGase activity was studied (Figure 5). A well defined maximum of enzyme activity was observed for the mutant strain after 20h of growing; while activity of wild strain did not significantly vary during growth.

S-adenosyl-L-methionine: its effect on aminolevulinate dehydratase and glutathione in acute ethanol intoxication

The effect of disulfiram and S-adenosyl-L-methionine (SAM) administration to acute ethanol intoxicated mice on the hepatic glutathione (GSH) concentration and aminolevulinic and dehydratase (ALA-D) activity was investigated. It was found that both GSH levels and ALA-D activity were decreased, and evidence suggested that the toxic action of ethanol was due to its conversion into acetaldehyde. Administration of SAM reverses the effects of acute alcohol abuse by increasing liver GSH availability. In vitro, hepatic ALA-D activity was not modified by ethanol; instead it was non-competitively inhibited by acetaldehyde. This inhibition was efficiently reversed by GSH and cysteine (CySH). Therefore, a mechanism for the action of ethanol on ALA-D, based on the inhibitory effect of acetaldehyde, is proposed.

Human red cell porphobilinogen deaminase. A simpler method of purification and some unusual properties

A simpler method for purifying human red cell deaminase, using a mixture of n-butanol and chloroform, which denatures hemoglobin, followed by ammonium sulphate fractionation, heat treatment, Sephadex G-100 and DEAE-cellulose chromatography, yielding a 3400 fold purified enzyme is described. Some properties of purified deaminase were studied. The enzyme seems to have a strict requirement for oxygen, neither PBG consumption nor uroporphyrinogens formation were measured under anaerobiosis. Uroporphyrinogens formation was linear with both protein and time over a wide range of enzyme concentration and up to 2 h. The optimum pH was 7.4 and the mol. wt was 40,000 +/- 4000. The enzyme was heat-stable and increased its activity by heating. Ammonium and hydroxylamine ions inhibited the reaction. K+ and Na+ ions did not greatly affect activity, while most divalent cations tested significantly diminished uroporphyrinogen formation and to a lesser degree PBG consumption. Direct plots of velocity against PBG concentration were hyperbolic, however double-reciprocal plots were non-linear, Hill plots gave an n value of 2 and Eadie plots were bell-shaped, indicating the existence of weakly positive cooperative effect between 2 binding sites for PBG per molecule of deaminase.