Substrate specificity of african oil palm tree peroxidase

The optimal conditions for catalysis by the peroxidase isolated from leaves of African oil palm tree (AOPTP) have been determined. The pH optimum for oxidation of the majority of substrates studied in the presence of AOPTP is in the interval of 4.5-5.5. A feature of AOPTP is low pH value (3.0) at which the peroxidase shows its maximal activity toward 2,2"-azino-bis(3-ethylbenz-thiazoline-6-sulfonic acid) (ABTS). Increasing the buffer concentration changes the AOPTP activity, the degree of the effect depending upon the chemical structure of the substrate. Under optimal conditions of AOPTP catalysis, the values of second order rate constant characterizing efficiency of enzymatic oxidation of substrates have been calculated. It was shown that among 12 peroxidase substrates studied, ABTS and ferulic acid are the best substrates for AOPTP. The results show that substrate specificities of AOPTP and royal palm tree peroxidase are similar, but different from substrate specificity of other plant peroxidases.     

Substrate specificity in phospholipid transformations by plant phospholipase D isoenzymes

Phospholipase D (PLD) catalyzes the hydrolysis and transesterification of glycerophospholipids at the terminal phosphodiester bond. In many plants, several isoforms of PLD have been identified without knowing their functional differences. In this paper, the specificities of two PLD isoenzymes from white cabbage (Brassica oleracea var. capitata) and two ones from opium poppy (Papaver somniferum L.), which were recombinantly produced in Escherichia coli, were compared in the hydrolysis of phospholipids with different head groups and in the transphosphatidylation of phosphatiylcholine with several acceptor alcohols. In a biphasic reaction system, consisting of buffer and diethyl ether, the highly homologous isoenzymes are able to hydrolyze phosphatidylcholine, -glycerol, -ethanolamine, -inositol and - with one exception - also phosphatidylserine but with different individual reaction rates. In transphosphatidylation of phosphatidylcholine, they show significant differences in the rates of head group exchange but with the same trend in the preference of acceptor alcohols (ethanolamine > glycerol ? l-serine). For l- and d-serine a stereoselectivity of PLD was observed. The results suggest a physiological relevance of the different hydrolytic and transphosphatidylation activities in plant PLD isoenzymes.     

Substrate specificity of lignin peroxidase and a S168W variant of manganese peroxidase

Lignin peroxidase (LiP) and manganese peroxidase (MnP) are structurally similar heme-containing enzymes secreted by white-rot fungi. Unlike MnP, which is only specific for Mn(2+), LiP has broad substrate specificity, but it is not known if this versatility is due to multiple substrate-binding sites. We report here that a S168W variant of MnP from Phanerochaete chrysosporium not only retained full Mn(2+) oxidase activity, but also, unlike native or recombinant MnP, oxidized a multitude of LiP substrates, including small molecule and polymeric substrates. The kinetics of oxidation of most nonpolymeric substrates by the MnP variant and LiP were similar. The stoichiometries for veratryl alcohol oxidation by these two enzymes were identical. Some readily oxidizable substrates, such as guaiacol and ferrocyanide, were oxidized by MnP S168W and LiP both specifically and nonspecifically while recombinant MnP oxidized these substrates only nonspecifically. The functional similarities between this MnP variant and LiP provide evidence for the broad substrate specificity of a single oxidation site near the surface tryptophan.     

Substrate specificity of rat sera IgG antibodies with peroxidase and oxidoreductase activities

We have recently shown that intact IgGs from the sera of healthy Wistar rats oxidize 3,3'-diaminobenzidine (DAB) in the presence and in the absence of H(2)O(2) similar to horseradish peroxidase (HRP). Here we demonstrate for the first time that the peroxidase and oxidoreductase activities of IgGs can efficiently oxidize not only DAB but also o-phenylendiamine, phenol, p-dihydroquinone, alpha-naphthol, and NADH but, in contrast to HRP, cannot oxidize adrenalin. In contrast to IgGs, HRP cannot oxidize phenol, p-dihydroquinone, or alpha-naphthol in the absence of H(2)O(2). In contrast to plant and mammalian peroxidases, IgGs were more universal in their metal dependence. The specific wide repertoire of polyclonal peroxidase and oxidoreductase IgGs oxidizing various substances could play an important role in protecting the organism from oxidative stress and serve as an additional natural system destroying different toxic, carcinogenic, and mutagenic compounds.     

Binding of hydrogen donors to horseradish peroxidase: A spectroscopic study

Absorption spectroscopy measurements of the binding of aromatic donors and competitive inhibitors to horseradish peroxidase indicate that they are bound to the enzyme through hydrophobic forces and hydrogen bonding. Nuclear magnetic resonance experiments show that the minimal distances between the enzyme iron and the protons of a typical donor, p-cresol, are 7.0 ± 0.5, 7.7 ± 0.5 and 8.5 ± 0.5 Å, for the ortho-, meta- and methyl-protons, respectively.A model for the binding of aromatic donors to horseradish peroxidase based on this result is presented. It is proposed that the aromatic ring is attached to a hydrophobic region in the protein interior and the phenol oxygen is hydrogen-bonded to the pyrrolic nitrogen of the iron-coordinated histidine. This structure is compatible with the proton-iron distances measured and offers an intramolecular path for electron conduction from donor to heme analogous to that proposed by Winfield for the peroxidases.     

Kinetics of fenugreek peroxidase isoenzymes

Peroxidase from fenugreek seedlings was separated into 6 isoenzymes; 4 on CM-cellulose and 2 on DEAE-cellulose. The kinetics of these peroxidase isoenzymes with regard to o-dianisidine and catechol are described.     

Genetics of the peroxidase isoenzymes inPetunia

Summary The structural geneprxD inPetunia codes for a slow moving anodic peroxidase whose activity is sensitive to high concentrations of hydrogen peroxide. The PRXd enzyme could be found in mature and old leaf and stem tissue of full-grown flowering plants. PRXd was found to be absent in tissues from flower corolla and root. The geneprxD is the fourth gene that codes for peroxidases in leaf and stem. Two mobility variants of the PRXd enzyme have been found among our inbred lines using starch gel system II electrophoresis. The geneprxD could be located on chromosome III by a four-point-cross involving the genesprxA, prxD, Mf1 andHt1. The order of the genes established is:Ht1 — Mf1 — prxD — prxA.     

Germinating barley selenium-containing peroxidase is one of the peroxidase isoenzymes

A selenium-containing peroxidase from the germinating barley grown on a selenium-containing artificial medium was isolated and purified by means of cold acetone precipitation, Sephadex-G150 filtration, followed by DEAE-Sepharose chromatography and sodium dodecyl sulfate — polyacrylamid gel electrophoresis. The form of selenium existing in the peptide assayed with paper chromatography was selenomethionine. The amino acid composition of this enzyme was similar to those peroxidases from other sources except amino acids Glu, Val Phe, Lys, and Arg. Electron-spin resonance (ESR) spectra recorded at −136°C showed that both the selenium-containing peroxidase from germinating barley and horseradish peroxidase had same the ESR signals as iron protoporphyine. Those results suggested that the germinating barley selenium-containing peroxidase is one of the peroxidase isoenzymes.     

Genetics of the peroxidase isoenzymes in Petunia

Summary As detected by starch gel electrophoresis, the fast moving anodal group of peroxidase isoenzymes, the PRXa complex, of a Petunia homozygous for the encoding gene can be made up of one to four bands, depending on the tissue sampled, the age of the tissue and of the plant, and the genetic background. Additional evidence is presented showing that the PRXa complex is encoded by one structural gene, prxA, rather than by tandem duplicated genes. On the basis of electrophoretic variation in Petunia hybrida and related species, five prxA alleles were found. A prxA internal site mutation was found recognized by the absence of recombination between the mutation that affected the temporal programme of the gene and the mutation that altered the mobility of the enzyme. By a three-point test, the gene prxA was located on chromosome III and found to be linked to the genes Mf1 and Ht1 in the order prxA-Mf1-Ht1. The construction of a trisomic III triply heterozygous for prxA confirmed the location of prxA.     

Regulation and function of ascorbate peroxidase isoenzymes

Even under optimal conditions, many metabolic processes, including the chloroplastic, mitochondrial, and plasma membrane-linked electron transport systems of higher plants, produce active oxygen species (AOS). Furthermore, the imposition of biotic and abiotic stress conditions can give rise to excess concentrations of AOS, resulting in oxidative damage at the cellular level. Therefore, antioxidants and antioxidant enzymes function to interrupt the cascades of uncontrolled oxidation in each organelle. Ascorbate peroxidase (APX) exists as isoenzymes and plays an important role in the metabolism of H(2)O(2) in higher plants. APX is also found in eukaryotic algae. The characterization of APX isoenzymes and the sequence analysis of their clones have led to a number of investigations that have yielded interesting and novel information on these enzymes. Interestingly, APX isoenzymes of chloroplasts in higher plants are encoded by only one gene, and their mRNAs are generated by alternative splicing of the gene's two 3'-terminal exons. Manipulation of the expression of the enzymes involved in the AOS-scavenging systems by gene-transfer technology has provided a powerful tool for increasing the present understanding of the potential of the defence network against oxidative damage caused by environmental stresses. Transgenic plants expressing E. coli catalase to chloroplasts with increased tolerance to oxidative stress indicate that AOS-scavenging enzymes, especially chloroplastic APX isoenzymes are sensitive under oxidative stress conditions. It is clear that a high level of endogenous ascorbate is essential effectively to maintain the antioxidant system that protects plants from oxidative damage due to biotic and abiotic stresses.     

Genetics of the peroxidase isoenzymes in Petunia

Theoretical and Applied Genetics - In Petunia four alleles of the gene prxB could be identified by starch gel electrophoresis. Investigation of PRXb allozyme balance during development of tissue...     

Genetics of the peroxidase isoenzymes in Petunia

Summary By starch gel electrophoresis three mobility variants of a cathodic moving doublet of bands, encoded by the structural gene prxC, were detected in all organs of flowering petunias. In root tissue two of the variants showed a lower electrophoretic mobility than in other organs. During development of flower buds the PRXc enzymes showed an increase in mobility. The gene prxC was located on chromosome IV by showing linkage to the genes An3 and Dw1, by trisomic segregation, and by the construction of triply heterozygous trisomics IV. The gene order on chromosome IV is B1-An3/Dw1-prxC. It was concluded that the temporal programming difference in the expression of the alleles prxC2 and prxC3 is caused by internal site mutation. Analysis of progeny obtained by crossing of lines to the trisomic IV with genotype prxC1/C1/C2 showed differential expression of the two prxC1 alleles of the trisomic IV.     

Genetics of the peroxidase isoenzymes in Petunia

Summary Three electrophoretic variants of the peroxidase b isoenzymes in Petunia have been found. The encoding gene prxB is shown to be located on chromosome I by its linkage with the gene Hfl. Analysis of prxB heterozygotes showed a gradual increase of the electrophoretic mobility of all three PRXb allozymes during development and differential expression in enzyme activity of three prxB alleles. The location of prxB on chromosome I was confirmed by an allelic dosage effect in trisomies I, trisomie segregation and the construction of trisomies I with triple-banded PRXb phenotype. From telotrisomic analysis it was concluded that prxB and Hfl are located on the same arm of chromosome I. The unexpected linkage of prxB and Hfl with the gene Fl in one of the crosses was suggested to be caused by a translocation in line SI, involving the gene Fl.     

Genetics of the peroxidase isoenzymes in Petunia

Summary Antibodies were raised against the peroxidases encoded by the allele prxA1 to determine the specific activities of the peroxidases encoded by the alleles prxA1, prxA2, prxA3, and prxA5. The results from double diffusion experiments indicated that all peroxidases encoded by the four alleles are antigenically identical. By rocket immuno electrophoresis it was shown that the peroxidases encoded by the alleles prxA1, prxA2, prxA3, and prxA5 have different specific activities. The results presented are discussed in relation to differential expression of the alleles involved.     

Genetics of the peroxidase isoenzymes in Petunia

Summary Two alleles of the structural gene prxA from Petunia, prxA6 and prxA7, could be identified by their differential temporal expression. The alleles prxA6 and prxA7 code for peroxidases with a similar electrophoretic mobility as the products of the previously described alleles prxA1 and prxA5, respectively. The former two alleles differ in that they have a different temporal expression with regard to the temporal expression of the allele prxA2. Crossing experiments indicated that the mutations involved are (cisacting) internal site mutations. In the case of the allele prxA6, the experiments indicated a difference with respect to the allele prxA1 in responsiveness to the action of a trans-acting factor.     

Genetics of the peroxidase isoenzymes in Petunia

Summary The structural gene prxE, coding for a slow cathodic peroxidase in Petunia, has been located to chromosome II, linked to F1. The presence of two mobility alleles in Petunia hybrida can be ascribed to its hybrid descent. Some properties of peroxidase e are mentioned. A gene prxJ is postulated for a still slower cathodic band. The gene Rp1, regulating the onset of expression of the allele prxB2, has been located on chromosome VII (gene order Rp1-prxF-An4). A synopsis of the isoperoxidases and the corresponding genes is given.