Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P06889 (Mol)
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The final step in heme synthesis is catalyzed by the mitochondrial enzyme, ferrochelatase. Characterization of this enzyme has been complicated by a number of factors including the dependence of enzyme activity on lipids. Purification of ferrochelatase from rat and bovine sources has been achieved only relatively recently using blue Sepharose CL-6B chromatography. When 3,5-diethoxycarbonyl-1,4-dihydro-2,4,6-trimethylpyridine (DDC) is given to animals, it produces a hepatic porphyria resembling human variegate porphyria thus providing an experimental system in which to study this disease. DDC has been found to cause the accumulation of a green pigment, identified as N-methyl protoporphyrin IX (N-MePP), which is a potent inhibitor of ferrochelatase. The source of the N-methyl substituent of N-MePP was found to be the 4-methyl group of DDC. Considerable evidence indicates that the protoporphyrin IX moiety of N-MePP originates from the heme moiety of cytochrome P-450 and that DDC is a suicide substrate for this hemoprotein. Some studies suggest that cytochrome P-450 isozymes differ in their susceptibility to destruction by DDC and its 4-alkyl analogues. Griseofulvin has also been reported to inhibit hepatic ferrochelatase in rodents but not in the 17-day old chick embryo nor in hepatocyte culture systems. Thus, the mechanism by which griseofulvin produces an experimental porphyria in chick embryo liver cell culture is different from that for rodents.
Mol Cell Biochem 1984 Sep
PMID:Ferrochelatase and N-alkylated porphyrins. 639 Jan 67

We have studied the kinetics of the inhibition of mitochondrial protoporphyrinogen oxidase (PPO) from liver and placenta of 3 mammalian species by the diphenyl ether herbicide acifluorfen (AF). AF competitively inhibited PPO from human liver and placenta, mouse liver and pig placenta with respect to its substrate protoporphyrinogen. In contrast, mixed-type inhibition was shown for pig liver. The differing results shown in pig liver may point to structural differences in PPO derived from different species and tissues. We have also compared the effects of AF on the function of PPO in human lymphoblasts from normal subjects and those with variegate porphyria, an inherited disorder of PPO. Competitive inhibition was shown for both and there were no significant differences in the values of Ks or Ki.
Biochem Mol Biol Int 1994 Dec
PMID:Inhibition of mammalian protoporphyrinogen oxidase by acifluorfen. 769 1

Mutation analysis of genomic DNA samples obtained from 17 unrelated South African patients with variegate porphyria (VP) revealed three novel missense mutations in the protoporphyrinogen oxidase (PPOX) gene. A common C to T transition at nucleotide position 452 (R59W) was identified in 15 of the patients analysed, while base changes at positions 336 (H20P) and 779 (R168C) were identified in the remaining two patients. Using protein analysis software we were able to predict that all three mutations have a similar biophysical effect on the protein, being the disturbance of amphiphatic regions within the protein, which might result in misfolding of the protein. Mutation R59W, identified in the majority of South African VP families, was shown to create a Styl restriction site, while mutation R168C would abolish a Dsal restriction site in genomic DNA of affected individuals. As 100% of the index patients analysed were molecularly characterized, the combined use of restriction enzyme and single-strand conformation polymorphism (SSCP) analysis now allows a rapid and accurate diagnosis of VP in South Africa. Mutation R59W was furthermore shown to be in association with one of four potential haplotypes defined by two newly described polymorphisms in exon 1 of the PPOX gene. Our molecular data thus strongly support the founder hypothesis for VP in South Africa.
Hum Mol Genet 1996 Jul
PMID:Identification of three mutations and associated haplotypes in the protoporphyrinogen oxidase gene in South African families with variegate porphyria. 881 34

Variegate porphyria (VP) is an acute hepatic porphyria with autosomal dominant inheritance due to a partial deficiency of protoporphyrinogen oxidase (PPOX) activity. The molecular defect responsible for VP was investigated by sequencing PPOX gene coding sequence from four patients in three unrelated VP families of French Caucasian origin. In a first patient, a point insertion of a G at position 1022 of the cDNA, produced a frameshift resulting in a premature stop codon. In three other patients from two unrelated families we found a missense point mutation leading to glycine to arginine substitution (G232R) in exon 7. This Gly232 appears to be a strictly conserved residue through evolution. In one VP family, we observed the cosegregation of the G232R missense mutation and the deficient PPOX activity. The mutations reported here are the first to be described in patients with VP and support the conclusion that PPOX gene defects are disease causing mutations in human variegate porphyria.
Hum Mol Genet 1996 Mar
PMID:Mutations in the protoporphyrinogen oxidase gene in patients with variegate porphyria. 885 67

Hepatic porphyrias are characterized by neurological symptoms manifested by abdominal pain, neuropathies and mental aberrations. Porphyrins are ubiquitous and essential biochemical constituents of living beings acting as mediators of oxidation reaction in the metabolism of the steroid, drugs, environmental chemicals or as a mean of exchanging gases, such as oxygen and carbon dioxide between the environment and the tissue of the body using endogenous polypeptide properties. The different porphyrins arising from the arrangement of normal heme synthesis are characterized by an accumulation and excretion of specific intermediate porphyrins and/or of precursors exerting toxic effect, initiating cascades of generations of polypeptides, neurotransmitters and gut-brain axis peptide responsible for the symptoms of clinical status. We studied polypeptide levels in 27 patients (19 females, 8 males) presenting acute attack of hepatic porphyria: 2 with ALA dehydratase-deficient porphyria; 9 with acute intermittent porphyria; 12 with porphyria cutanea tarda and 4 with variegate porphyria. During acute attacks of porphyria, polypeptides were found to be constantly increased: vasoactive intestinal polypeptide (VIP); neurotensin (NT); substance P; pancreatic polypeptide; gastrin-releasing peptide; gastrin and motilin. Administration of the somatostatin (antagonizing polypeptide), which was undetectable or low before treatment, apparently alleviated the acute symptomatology. Elevated levels of polypeptides, at least partly, contribute to appearance of acute symptoms in porphyria patients.
Cell Mol Biol (Noisy-le-grand) 1997 Feb
PMID:Polypeptide levels increase during acute onset of hepatic porphyrias. 907 85

Protoporphyrinogen oxidase (E.C.1.3.3.4) (PPO) catalyzes the penultimate step in the heme biosynthetic pathway. Deficiency in activity of this enzyme results in the human genetic disease variegate porphyria. Herein we detail the cloning, expression, purification and characterization of the normal and variegate porphyria forms of human PPO. The cDNA sequence for human ppo is approximately 1.8 kb in length and codes for a protein of 477 amino acids. This protein, which does not contain a typical cleavable mitochondrial targeting sequence, is approximately 51 kDa and contains a putative dinucleotide binding motif near the amino terminus. The active enzyme is a homodimer and contains an FAD. Attachment of a six his amino terminal tag allows for the rapid and efficient purification of approximately 10 mg of enzyme from one liter of E. coli culture. Three variegate porphyria mutant PPO enzymes were expressed and characterized. These mutations, R59W, R168C and A433P, result in decreased enzyme activity by causing a decrease in kcat without a significant change in Km for the substrate protoporphyrinogen IX. Purified R59W lacks the FAD cofactor which may be explained by the fact that this mutation resides within the dinucleotide binding motif of PPO.
Cell Mol Biol (Noisy-le-grand) 1997 Feb
PMID:Characteristics of human protoporphyrinogen oxidase in controls and variegate porphyrias. 907 90

A subset of probands from 11 South African families with clinical and/or biochemical features of variegate porphyria (VP), but without the known protoporphyrinogen oxidase (PPOX) gene defects identified previously in the South African population, were subjected to mutation analysis. Disease-related mutation(s) could not be identified after screening virtually the entire PPOX gene by heteroduplex single-strand conformation polymorphism analysis (HEX-SSCP), although three new sequence variants were detected in exon 1 of the gene in three normal controls. The presence of these single base changes at nucleotide positions 22 (C/G), 27 (C/A) and 127 (C/A), in addition to the known exon 1 polymorphisms I-26 and I-150, indicates that this untranslated region of the PPOX gene is particularly mutation-prone. Furthermore, microsatellite markers flanking the PPOX and alpha-1 antitrypsin (PI) gene, on chromosomes 1 and 14, respectively, were used to assess the probability of involvement of these loci in disease presentation. Common alleles transmitted from affected parent to affected child were determined where possible in the mutation-negative index cases. Allelic frequencies of these <<disease-associated>> alleles were compared to findings in the normal population, but no predominant disease-associated allele could be identified. Co-segregation of a specific haplotype with the disease phenotype could also not be demonstrated in a large Afrikaner family. It is concluded that further studies are warranted to determine the genetic factor(s) underlying the autosomal dominant pattern of inheritance in molecularly uncharacterized cases showing clinical symptoms of an acute porphyria.
Mol Cell Probes 1998 Oct
PMID:Molecular analysis reveals a high mutation frequency in the first untranslated exon of the PPOX gene and largely excludes variegate porphyria in a subset of clinically affected Afrikaner families. 977 54

Variegate porphyria (VP) is a low penetrance, autosomal dominant disorder that results from partial deficiency of protoporphyrinogen oxidase (PPOX) activity caused by mutation in the PPOX gene. The rare homozygous variant of VP is characterized by severe PPOX deficiency, onset of photosensitization by porphyrins in early childhood, skeletal abnormalities of the hand and, less constantly, short stature, mental retardation and convulsions. We have identified PPOX mutations on both alleles of five of the 11 unrelated patients with homozygous VP reported to date. Two patients were homoallelic for missense mutations (D349A and A433P), while three were heteroallelic. Functional analysis by prokaryotic expression showed that the D349A and A433P and one missense mutation in each of the three heteroallelic patients (G358R in two patients and A219KANA) preserved some PPOX activity (9.5-25% of wild-type). Mutations on the other allele of the heteroallelic patients abolished or markedly decreased activity. There was no relation between genotype assessed by functional analysis and the presence or severity of non-cutaneous manifestations. The mutations were absent from 104 unrelated patients with autosomal dominant VP. Our findings define the molecular pathology of homozygous VP and suggest that mild PPOX mutations occur in the general population but have very low or no clinical penetrance in heterozygotes.
Hum Mol Genet 1998 Nov
PMID:Molecular characterization of homozygous variegate porphyria. 981 36

Mutation analysis was performed on DNA samples of 965 individuals from four different ethnic groups in South Africa, in an attempt to determine the spectrum of sequence variants in the haemochromatosis ( HFE ) gene. This population screening approach, utilizing a combined heteroduplex and single-strand conformation polymorphism (HEX-SSCP) method, revealed three previously described and four novel missense mutations. Novel variants V53M and V59M were identified in exon 2, Q127H in exon 3 and R330M in exon 5. The exon 5 variant was identified in one of 13 patients referred for a molecular diagnosis of hereditary haemochromatosis (HH), who tested negative for the known C282Y and H63D mutations. Mutation Q127H was detected in exon 3 of the HFE gene together with mutation H63D in an apparently severely affected patient previously shown to carry the protoporphyrinogen oxidase ( PPOX ) gene mutation R59W, which accounts for dominantly inherited variegate porphyria (VP) in >80% of affected South Africans. The mutant allele frequency of the C282Y mutation was found to be significantly lower in 73 apparently unrelated VP patients with the R59W mutation than in 102 controls drawn from the same population ( P = 0.005). The population screening approach used in this study revealed considerable genotypic variation in the HFE gene and supports previous data on the involvement of this gene in the porphyria phenotype.
Hum Mol Genet 1999 Aug
PMID:Spectrum of mutations in the HFE gene implicated in haemochromatosis and porphyria. 1040 Oct

Variegate porphyria is an autosomal dominant disorder of heme metabolism which results from decreased activity of the enzyme protoporphyrinogen oxidase. Clinically, the disease manifests postpubertally and is characterized by photocutaneous sensitivity and/or acute neurovisceral crises. However, in homozygous variegate porphyria, onset of the disease usually occurs in infancy with severe skin manifestations. The molecular basis of variegate porphyria in two severely affected probands in two South African families is described. Mutation detection included combined SSCP-heteroduplex analysis followed by direct sequencing. The unrelated probands both had the common R59W mutation while the other lesion was Y348C or R138P (both novel mutations), causing homozygous variegate porphyria.
Mol Genet Metab 2000 Apr
PMID:Homozygous variegate porphyria in South Africa: genotypic analysis in two cases. 1087 Aug 50


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