Publications

• Expression of a cloned protoporphyrinogen oxidase.

  Dailey T.A., Meissner P., Dailey H.A.

  The previously cloned hem Y gene of Bacillus subtilis (Hansson, M., and Hederstedt, L. (1992) J. Bacteriol. 174, 8081-8093) has been expressed in Escherichia coli. The expressed protein has been shown to be the penultimate enzyme of the heme biosynthetic pathway, protoporphyrinogen oxidase (EC 1.3 ... >> More

  The previously cloned hem Y gene of Bacillus subtilis (Hansson, M., and Hederstedt, L. (1992) J. Bacteriol. 174, 8081-8093) has been expressed in Escherichia coli. The expressed protein has been shown to be the penultimate enzyme of the heme biosynthetic pathway, protoporphyrinogen oxidase (EC 1.3.3.4) and, thus, the gene designation should be hem G. This represents the first report of the expression of a cloned protoporphyrinogen oxidase from any source. The enzyme is present in the soluble cytoplasmic fraction and is, thus, unlike all previously reported eukaryotic or prokaryotic protoporphyrinogen oxidases, which are membrane-bound. It utilizes molecular oxygen as a terminal electron acceptor, and protoporphyrinogen IX, mesoporphyrinogen IX, and coproporphyrinogen III serve as substrates. The diphenyl ether herbicide acifluorfen, which is a strong inhibitor of the eukaryotic enzyme, is only weakly inhibitory. The enzyme has a predicted molecular weight of 51,200, which corresponds well with molecular weight determination via high performance liquid chromatography and SDS-polyacrylamide gel electrophoresis. In addition the enzyme contains a putative dinucleotide binding region at the amino terminus, which is consistent with the previously demonstrated presence of a flavin moiety in the characterized mammalian enzymes. << Less

  J. Biol. Chem. 269:813-815(1994) [PubMed] [EuropePMC]

• Cloning, sequence, and expression of mouse protoporphyrinogen oxidase.

  Dailey T.A., Dailey H.A., Meissner P., Prasad A.R.

  Protoporphyrinogen oxidase (EC 1.3.3.4) is the penultimate enzyme in the heme biosynthetic pathway, catalyzing the six-electron oxidation of protoporphyrinogen to protoporphyrin. A dominantly inherited genetic deficiency in this enzyme results in the disease variegate porphyria. We now report the ... >> More

  Protoporphyrinogen oxidase (EC 1.3.3.4) is the penultimate enzyme in the heme biosynthetic pathway, catalyzing the six-electron oxidation of protoporphyrinogen to protoporphyrin. A dominantly inherited genetic deficiency in this enzyme results in the disease variegate porphyria. We now report the cloning, sequence, and expression of mouse protoporphyrinogen oxidase. The cDNA for mouse protoporphyrinogen oxidase was obtained by complementation of Escherichia coli SASX38, a protoporphyrinogen oxidase-deficient strain, with a mouse erythroleukemia (MEL) cell expression library. The sequence of this cDNA along with 5' untranslated sequence obtained by 5' rapid amplification of cDNA ends of MEL cell mRNA is 1814 bp in length and contains an open reading frame of 1431 bp. This encodes a protein of 477 amino acid residues with a calculated molecular weight of 50,870. The protein as expressed in E. coli is sensitive to inhibition by the diphenyl ether herbicide acifluorfen. Northern blot analyses of RNA from uninduced and induced MEL cells as well as mouse hepatoma cells all show two major mRNA species of 1.8 and 3.6 kb. << Less

  Arch. Biochem. Biophys. 324:379-384(1995) [PubMed] [EuropePMC]

• Functional studies of mutations in the human protoporphyrinogen oxidase gene in variegate porphyria.

  Morgan R.R., da S.V., Puy H., Deybach J.C., Elder G.H.

  The autosomal dominant disorder, variegate porphyria (VP), results from mutations in the protoporphyrinogen oxidase (PPOX) gene. We have investigated the effects of 22 disease-associated missense mutations in this gene on enzyme activity. Mutants were generated in the expression plasmid pHPPOX by ... >> More

  The autosomal dominant disorder, variegate porphyria (VP), results from mutations in the protoporphyrinogen oxidase (PPOX) gene. We have investigated the effects of 22 disease-associated missense mutations in this gene on enzyme activity. Mutants were generated in the expression plasmid pHPPOX by site-directed mutagenesis. They were screened for PPOX activity by complementation of the Escherischia coli strain SAS38X which lacks PPOX activity. Ten mutants (G40E, L85P, G232R, de1281H, V282D, L295P, V335G, S350P, L444P, G453V) had no detectable PPOX activity. PPOX activity of the remaining 12 mutants (L15F, R38P, L73P, V84G, D143V, R152C, L154P, V158M, R168H, A172V, V290L, G453R) ranged from less than 1% to 9.2% of wild-type activity. Our findings show that all 22 mutations substantially impair or abolish PPOX activity in a prokaryotic expression system and add to the evidence that they cause VP. << Less

  Cell Mol Biol (Noisy-le-grand) 48:79-82(2002) [PubMed] [EuropePMC]

• Site-directed mutagenesis and computational study of the Y366 active site in Bacillus subtilis protoporphyrinogen oxidase.

  Sun L., Wen X., Tan Y., Li H., Yang X., Zhao Y., Wang B., Cao Q., Niu C., Xi Z.

  Protoporphyrinogen IX oxidase (PPO), the last common enzyme of heme and chlorophyll biosynthesis, catalyses the oxidation of protoporphyrinogen IX to protoporphyrin IX, with FAD as cofactor. Among PPO, Bacillus subtilis PPO (bsPPO) is unique because of its broad substrate specificity and resistanc ... >> More

  Protoporphyrinogen IX oxidase (PPO), the last common enzyme of heme and chlorophyll biosynthesis, catalyses the oxidation of protoporphyrinogen IX to protoporphyrin IX, with FAD as cofactor. Among PPO, Bacillus subtilis PPO (bsPPO) is unique because of its broad substrate specificity and resistance to inhibition by diphenylethers. Identification of the activity of bsPPO would help us to understand the catalysis and resistance mechanisms. Based on the modeling and docking studies, we found that Y366 site in bsPPO was adjacent to substrate and FAD. In order to evaluate the functional role of this site, three mutants Y366A Y366E and Y366H were cloned and kinetically characterized. The efficiency of catalysis for Y366A and Y366H reduced to 10% of the wild-type enzyme's activity, while Y366E just retained 1%. Y366E shows large resistance (K (i) = 153.94 microM) to acifluorfen. Molecular docking was carried out to understand the structure and functional relationship of PPO. The experimental results from the site-directed mutagenesis are consistent with the computational studies. The residue at position 366 is seemed to be responsible for substrate binding and catalysis and involved in herbicide resistance of bsPPO. << Less

  Amino Acids 37:523-530(2009) [PubMed] [EuropePMC]

• Protoporphyrinogen oxidase of Myxococcus xanthus. Expression, purification, and characterization of the cloned enzyme.

  Dailey H.A., Dailey T.A.

  Protoporphyrinogen oxidase (EC 1.3.3.4) catalyzes the six electron oxidation of protoporphyrinogen IX to protoporphyrin IX. The enzyme from the bacterium Myxococcus xanthus has been cloned, expressed, purified, and characterized. The protein has been expressed in Escherichia coli using a Tac promo ... >> More

  Protoporphyrinogen oxidase (EC 1.3.3.4) catalyzes the six electron oxidation of protoporphyrinogen IX to protoporphyrin IX. The enzyme from the bacterium Myxococcus xanthus has been cloned, expressed, purified, and characterized. The protein has been expressed in Escherichia coli using a Tac promoter-driven expression plasmid and purified to apparent homogeneity in a rapid procedure that yields approximately 10 mg of purified protein per liter of culture. Based upon the deduced amino acid sequence the molecular weight of a single subunit is 49,387. Gel permeation chromatography in the presence of 0.2% n-octyl-beta-D-glucopyranoside yields a molecular weight of approximately 100,000 while SDS gel electrophoresis shows a single band at 50,000. The native enzyme is, thus, a homodimer. The purified protein contains a non-covalently bound FAD but no detectable redox active metal. The M. xanthus enzyme utilizes protoporphyrinogen IX, but not coproporphyrinogen III, as substrate and produces 3 mol of H2O2/mol of protoporphyrin. The apparent Km and kcat for protoporphyrinogen in assays under atmospheric concentrations of oxygen are 1.6 microM and 5.2 min-1, respectively. The diphenyl ether herbicide acifluorfen at 1 microM strongly inhibits the enzyme's activity. << Less

  J. Biol. Chem. 271:8714-8718(1996) [PubMed] [EuropePMC]

• Quantitative structural insight into human variegate porphyria disease.

  Wang B., Wen X., Qin X., Wang Z., Tan Y., Shen Y., Xi Z.

  Defects in the human protoporphyrinogen oxidase (hPPO) gene, resulting in ~50% decreased activity of hPPO, is responsible for the dominantly inherited disorder variegate porphyria (VP). To understand the molecular mechanism of VP, we employed the site-directed mutagenesis, biochemical assays, stru ... >> More

  Defects in the human protoporphyrinogen oxidase (hPPO) gene, resulting in ~50% decreased activity of hPPO, is responsible for the dominantly inherited disorder variegate porphyria (VP). To understand the molecular mechanism of VP, we employed the site-directed mutagenesis, biochemical assays, structural biology, and molecular dynamics simulation studies to investigate VP-causing hPPO mutants. We report here the crystal structures of R59Q and R59G mutants in complex with acifluorfen at a resolution of 2.6 and 2.8 Å. The r.m.s.d. of the Cα atoms of the active site structure of R59G and R59Q with respect to the wild-type was 0.20 and 0.15 Å, respectively. However, these highly similar static crystal structures of mutants with the wild-type could not quantitatively explain the observed large differences in their enzymatic activity. To understand how the hPPO mutations affect their catalytic activities, we combined molecular dynamics simulation and statistical analysis to quantitatively understand the molecular mechanism of VP-causing mutants. We have found that the probability of the privileged conformations of hPPO can be correlated very well with the k(cat)/K(m) of PPO (correlation coefficient, R(2) > 0.9), and the catalytic activity of 44 clinically reported VP-causing mutants can be accurately predicted. These results indicated that the VP-causing mutation affect the catalytic activity of hPPO by affecting the ability of hPPO to sample the privileged conformations. The current work, together with our previous crystal structure study on the wild-type hPPO, provided the quantitative structural insight into human variegate porphyria disease. << Less

  J. Biol. Chem. 288:11731-11740(2013) [PubMed] [EuropePMC]

• Identification of an FAD superfamily containing protoporphyrinogen oxidases, monoamine oxidases, and phytoene desaturase. Expression and characterization of phytoene desaturase of Myxococcus xanthus.

  Dailey T.A., Dailey H.A.

  A large number of FAD-containing proteins have previously been shown to contain a signature sequence that is referred to as the dinucleotide binding motif. Protoporphyrinogen oxidase (PPO), the penultimate enzyme of the heme biosynthetic pathway, is an FAD-containing protein that catalyzes the six ... >> More

  A large number of FAD-containing proteins have previously been shown to contain a signature sequence that is referred to as the dinucleotide binding motif. Protoporphyrinogen oxidase (PPO), the penultimate enzyme of the heme biosynthetic pathway, is an FAD-containing protein that catalyzes the six electron oxidation of protoporphyrinogen IX. Sequence analysis demonstrates the presence of the dinucleotide binding motif at the amino-terminal end of the protein. Analysis of the current data base reveals that PPO has significant sequence similarities to mammalian monoamine oxidases (MAO) A and B, as well as to bacterial and plant phytoene desaturases (PHD). Previously MAOs have been shown to contain FAD, but there are no publications demonstrating the presence of FAD in purified PHDs. We have carried out the expression and purification of PHD from the bacterium Myxococcus xanthus and demonstrate the presence of noncovalently bound FAD. Sequence analysis demonstrate that PPO is closely related to bacterial PHDs and more distantly to plant PHDs and animal MAOs. Interestingly bacterial MAOs are no more closely related to PPOs, PHDs, and animal MAO's than they are to the unrelated Pseudomonas phenyl hydroxylase. All of the related sequences contain not only the basic putative dinucleotide binding motif that is found frequently for FAD-binding proteins, but they also have high similarity in an approximately 60-residue long region that extends beyond the dinucleotide motif. This region is not found among any other proteins in the current data base and, therefore, we propose that this region is a signature motif for a superfamily of FAD-containing enzymes that is comprised of PPOs, animal MAOs, and PHDs. << Less

  J Biol Chem 273:13658-13662(1998) [PubMed] [EuropePMC]

• Induction of terminal enzymes for heme biosynthesis during differentiation of mouse erythroleukemia cells.

  Taketani S., Yoshinaga T., Furukawa T., Kohno H., Tokunaga R., Nishimura K., Inokuchi H.

  To examine the induction of terminal enzymes of the heme-biosynthetic pathway during erythroid differentiation, mouse protoporphyrinogen oxidase (PPO) cDNA has been cloned. The deduced amino acid sequence derived from the nucleotide sequence revealed that mouse PPO consists of 477 amino acid resid ... >> More

  To examine the induction of terminal enzymes of the heme-biosynthetic pathway during erythroid differentiation, mouse protoporphyrinogen oxidase (PPO) cDNA has been cloned. The deduced amino acid sequence derived from the nucleotide sequence revealed that mouse PPO consists of 477 amino acid residues, without the leader peptide, which is imported into mitochondria. Comparison of the amino terminus of the deduced amino acid sequence of mouse PPO cDNA with that of purified bovine PPO provided conclusive evidence for lack of the leader peptide in the former. The amino acid sequence has 86% and 28% identity with human PPO and Bacillus subtilis HemY, respectively. When mouse erythroleukemia (MEL) cells were induced with dimethylsulfoxide, PPO mRNA was induced within 12 h of treatment, and with further incubation, reached a plateau. mRNAs for coproporphyrinogen oxidase (CPO) and ferrochelatase (FEC) were induced within 12 h, and continued to increase with time up to 48 h. The activities of CPO and FEC markedly increased with time up to 72 h, while PPO activity increased 1.8-fold within 12 h and remained unchanged thereafter. Immunoblot analysis showed that levels of PPO, CPO and FEC paralleled their corresponding activities. The magnitude of PPO induction was less than that of CPO and FEC. Thus, induction of three terminal enzymes of the heme-biosynthetic pathway is an early event in MEL cell differentiation. The concomitant induction may play an important role in producing large amounts of heme during erythroid differentiation. << Less

  Eur. J. Biochem. 230:760-765(1995) [PubMed] [EuropePMC]

• Mouse protoporphyrinogen oxidase. Kinetic parameters and demonstration of inhibition by bilirubin.

  Ferreira G.C., Dailey H.A.

  The penultimate step of haem biosynthesis, the oxidation of protoporphyrinogen to protoporphyrin, was examined with purified murine hepatic protoporphyrinogen oxidase (EC 1.3.3.4) in detergent solution. The kinetic parameters for the two-substrate (protoporphyrinogen and oxygen) reaction were dete ... >> More

  The penultimate step of haem biosynthesis, the oxidation of protoporphyrinogen to protoporphyrin, was examined with purified murine hepatic protoporphyrinogen oxidase (EC 1.3.3.4) in detergent solution. The kinetic parameters for the two-substrate (protoporphyrinogen and oxygen) reaction were determined. The limiting Km for protoporphyrinogen when oxygen is saturating is 6.6 microM, whereas the Km for oxygen with saturating concentrations of protoporphyrinogen is 125 microM. The kcat. for the overall reaction is 447 h-1. The ratio of kcat. to the Km for protoporphyrinogen is approx. 20-fold greater than the kcat./Km,O2 ratio. The ratio of protoporphyrin formed to dioxygen consumed is 1:3. Ubiquinone-6, ubiquinone-10 and dicoumarol stimulate protoporphyrinogen oxidase activity at low concentrations (less than 15 microM), whereas coenzyme Q0 and menadione show no activation at these concentrations. Above 30 microM, all five quinones inhibit the enzyme activity. FAD does not significantly affect the activity of the enzyme. Bilirubin, a product of haem catabolism, is shown to be a competitive inhibitor of the penultimate enzyme of the haem-biosynthetic pathway, protoporphyrinogen oxidase, with a calculated Ki of 25 microM. The terminal enzyme of haem-biosynthetic pathway, namely ferrochelatase, is not inhibited by bilirubin at concentrations over double the Ki value for the oxidase. In contrast with other enzymic systems, the toxicity of bilirubin is not reversed by binding to albumin. << Less

  Biochem J 250:597-603(1988) [PubMed] [EuropePMC]

• Crystal structure of protoporphyrinogen IX oxidase: a key enzyme in haem and chlorophyll biosynthesis.

  Koch M., Breithaupt C., Kiefersauer R., Freigang J., Huber R., Messerschmidt A.

  Protoporphyrinogen IX oxidase (PPO), the last common enzyme of haem and chlorophyll biosynthesis, catalyses the oxidation of protoporphyrinogen IX to protoporphyrin IX. The membrane-embedded flavoprotein is the target of a large class of herbicides. In humans, a defect in PPO is responsible for th ... >> More

  Protoporphyrinogen IX oxidase (PPO), the last common enzyme of haem and chlorophyll biosynthesis, catalyses the oxidation of protoporphyrinogen IX to protoporphyrin IX. The membrane-embedded flavoprotein is the target of a large class of herbicides. In humans, a defect in PPO is responsible for the dominantly inherited disease variegate porphyria. Here we present the crystal structure of mitochondrial PPO from tobacco complexed with a phenyl-pyrazol inhibitor. PPO forms a loosely associated dimer and folds into an FAD-binding domain of the p-hydroxybenzoate-hydrolase fold and a substrate-binding domain that enclose a narrow active site cavity beneath the FAD and an alpha-helical membrane-binding domain. The active site architecture suggests a specific substrate-binding mode compatible with the unusual six-electron oxidation. The membrane-binding domains can be docked onto the dimeric structure of human ferrochelatase, the next enzyme in haem biosynthesis, embedded in the opposite side of the membrane. This modelled transmembrane complex provides a structural explanation for the uncoupling of haem biosynthesis observed in variegate porphyria patients and in plants after inhibiting PPO. << Less

  EMBO J. 23:1720-1728(2004) [PubMed] [EuropePMC]

• Molecular characterization and subcellular localization of protoporphyrinogen oxidase in spinach chloroplasts.

  Che F.S., Watanabe N., Iwano M., Inokuchi H., Takayama S., Yoshida S., Isogai A.

  Protoporphyrinogen oxidase (Protox) is the last common enzyme in the biosynthesis of chlorophylls and heme. In plants, there are two isoenzymes of Protox, one located in plastids and other in the mitochondria. We cloned the cDNA of spinach (Spinacia oleracea) plastidal Protox and purified plastida ... >> More

  Protoporphyrinogen oxidase (Protox) is the last common enzyme in the biosynthesis of chlorophylls and heme. In plants, there are two isoenzymes of Protox, one located in plastids and other in the mitochondria. We cloned the cDNA of spinach (Spinacia oleracea) plastidal Protox and purified plastidal Protox protein from spinach chloroplasts. Sequence analysis of the cDNA indicated that the plastid Protox of spinach is composed of 562 amino acids containing the glycine-rich motif GxGxxG previously proposed to be a dinucleotide binding site of many flavin-containing proteins. The cDNA of plastidal Protox complemented a Protox mutation in Escherichia coli. N-terminal sequence analysis of the purified enzyme revealed that the plastidal Protox precursor is processed at the N-terminal site of serine-49. The predicted transit peptide (methionine-1 to cysteine-48) was sufficient for the transport of precursors into the plastid because green fluorescent protein fused with the predicted transit peptide was transported to the chloroplast. Immunocytochemical analysis using electron microscopy showed that plastidal Protox is preferentially associated with the stromal side of the thylakoid membrane, and a small portion of the enzyme is located on the stromal side of the chloroplast inner envelope membrane. << Less

  Plant Physiol. 124:59-70(2000) [PubMed] [EuropePMC]

• Structural insight into unique properties of protoporphyrinogen oxidase from Bacillus subtilis.

  Qin X., Sun L., Wen X., Yang X., Tan Y., Jin H., Cao Q., Zhou W., Xi Z., Shen Y.

  Protoporphyrinogen IX oxidase (PPO) converts protoporphyrinogen IX to protoporphyrin IX, playing an important part in the heme/chlorophyll biosynthetic pathway. Bacillus subtilis PPO (bsPPO) is unique among PPO family members in that it is a soluble monomer, is inefficiently inhibited by the herbi ... >> More

  Protoporphyrinogen IX oxidase (PPO) converts protoporphyrinogen IX to protoporphyrin IX, playing an important part in the heme/chlorophyll biosynthetic pathway. Bacillus subtilis PPO (bsPPO) is unique among PPO family members in that it is a soluble monomer, is inefficiently inhibited by the herbicide acifluorfen (AF) and has broader substrate specificity than other PPO enzymes. Here, we present the crystal structure of bsPPO bound to AF. Our structure shows that the AF molecule binds to a new site outside the previously identified inhibitor binding pocket. Most importantly, the benzene ring of the 2-nitrobenzoic acid moiety of AF lies parallel to the isoalloxazine ring of FAD at a distance of less than 3.5A, providing a framework for the interaction of FAD with the substrate protoporphyrinogen IX. Furthermore, our structure reveals that the larger substrate binding chamber and predominantly positively charged chamber surface of bsPPO are more favorable for the binding of coproporphyrinogen-III. These crystallographic findings uncover biochemically unique properties of bsPPO, providing important information for further understanding the enzymatic mechanism. << Less

  J. Struct. Biol. 170:76-82(2010) [PubMed] [EuropePMC]

  This publication is cited by 1 other entry.

• Structural insight into human variegate porphyria disease.

  Qin X., Tan Y., Wang L., Wang Z., Wang B., Wen X., Yang G., Xi Z., Shen Y.

  Human protoporphyrinogen IX oxidase (hPPO), a mitochondrial inner membrane protein, converts protoporphyrinogen IX to protoporphyrin IX in the heme biosynthetic pathway. Mutations in the hPPO gene cause the inherited human disease variegate porphyria (VP). In this study, we report the crystal stru ... >> More

  Human protoporphyrinogen IX oxidase (hPPO), a mitochondrial inner membrane protein, converts protoporphyrinogen IX to protoporphyrin IX in the heme biosynthetic pathway. Mutations in the hPPO gene cause the inherited human disease variegate porphyria (VP). In this study, we report the crystal structure of hPPO in complex with the coenzyme flavin adenine dinucleotide (FAD) and the inhibitor acifluorfen at a resolution of 1.9 Å. The structural and biochemical analyses revealed the molecular details of FAD and acifluorfen binding to hPPO as well as the interactions of the substrate with hPPO. Structural analysis and gel chromatography indicated that hPPO is a monomer rather than a homodimer in vitro. The founder-effect mutation R59W in VP patients is most likely caused by a severe electrostatic hindrance in the hydrophilic binding pocket involving the bulky, hydrophobic indolyl ring of the tryptophan. Forty-seven VP-causing mutations were purified by chromatography and kinetically characterized in vitro. The effect of each mutation was demonstrated in the high-resolution crystal structure. << Less

  FASEB J. 25:653-664(2011) [PubMed] [EuropePMC]

• Molecular cloning and characterization of a cDNA that encodes protoporphyrinogen oxidase of Arabidopsis thaliana.

  Narita S., Tanaka R., Ito T., Okada K., Taketani S., Inokuchi H.

  A cDNA encoding protoporphyrinogen oxidase (PPOX), the last enzyme common to the biosynthetic pathways for chlorophylls and hemes, was obtained from a library of Arabidopsis thaliana cDNA constructed in a lambda vector by screening for complementation of a hemG mutant of Escherichia coli. Extracts ... >> More

  A cDNA encoding protoporphyrinogen oxidase (PPOX), the last enzyme common to the biosynthetic pathways for chlorophylls and hemes, was obtained from a library of Arabidopsis thaliana cDNA constructed in a lambda vector by screening for complementation of a hemG mutant of Escherichia coli. Extracts of E. coli cells transformed with the Arabidopsis PPOX cDNA had high PPOX activity, and this activity was markedly inhibited by acifluorfen, a specific inhibitor of PPOX. Sequence analysis revealed that the cDNA for Arabidopsis PPOX encodes a protein of 537 amino acids (aa) with a calculated molecular mass of 57.7 kDa. The deduced aa sequence exhibited similarity to sequences of PPOX from Bacillus subtilis, mouse, and human. However, the PPOX of Arabidopsis contained a putative leader peptide for import into mitochondria (mt). southern analysis indicated that the PPOX whose cDNA we cloned is encoded by a single gene in Arabidopsis. Northern blot analysis showed that the level of expression of the gene in Arabidopsis leaves was high. whereas it was low in roots and floral buds. To our knowledge, this is the first report for the cloning of a cDNA for a plant PPOX. << Less

  Gene 182:169-175(1996) [PubMed] [EuropePMC]