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PubMed1995

Exchanging the extracellular domain of amyloid precursor protein for horseradish peroxidase does not interfere with alpha-secretase cleavage of the beta-amyloid region, but randomizes secretion in Madin-Darby canine kidney cells.

Secretory processing and polarized sorting of horseradish peroxidase fused to the amyloid precursor protein transmembrane domain were compared with those of wild-type amyloid precursor protein in COS and polarized Madin-Darby canine kidney (MDCK) cells. The cellular and secreted forms of the chimeric protein were enzymatically active in colorimetric and cytochemical assays after reconstitution with hemin and Ca2+. The peroxidase enzyme was secreted by a proteolytic process, similar to the parent amyloid precursor protein. In polarized MDCK cells, amyloid precursor protein was secreted exclusively in the basolateral compartment, while the peroxidase chimeric protein was secreted in both compartments. The basolateral sorting determinant for secretion must therefore be located in the extracellular domain of amyloid precursor protein. On the other hand, cell surface-associated peroxidase chimeric protein was similar to cell surface-associated wild-type amyloid precursor protein, mainly expressed at the basolateral side. The basolateral cell-surface expression, in contrast to the basolateral secretion, is therefore controlled by determinants in the cytoplasmic domain. Methylamine inhibited and bafilomycin slightly increased the basolateral secretion of both proteins, but both drugs strongly increased apical secretion. The default secretory pathway of COS cells and the basolateral (but not the apical) secretory pathway of MDCK cells are therefore comparably sensitive to methylamine and not to bafilomycin.

Amyloid Precursor Protein Secretases↗
PubMed1997

Mice deficient in cellular glutathione peroxidase develop normally and show no increased sensitivity to hyperoxia.

Glutathione peroxidase, a selenium-containing enzyme, is believed to protect cells from the toxicity of hydroperoxides. The physiological role of this enzyme has previously been implicated mainly using animals fed with a selenium-deficient diet. Although selenium deficiency also affects the activity of several other cellular selenium-containing enzymes, a dramatic decrease of glutathione peroxidase activity has been postulated to play a role in the pathogenesis of a number of diseases, particularly those whose progression is associated with an overproduction of reactive oxygen species, found in selenium-deficient animals. To further clarify the physiological relevance of this enzyme, a model of mice deficient in cellular glutathione peroxidase (GSHPx-1), the major isoform of glutathione peroxidase ubiquitously expressed in all types of cells, was generated by gene-targeting technology. Mice deficient in this enzyme were apparently healthy and fertile and showed no increased sensitivity to hyperoxia. Their tissues exhibited neither a retarded rate in consuming extracellular hydrogen peroxide nor an increased content of protein carbonyl groups and lipid peroxidation compared with those of wild-type mice. However, platelets from GSHPx-1-deficient mice incubated with arachidonic acid generated less 12-hydroxyeicosatetraenoic acid and more polar products relative to control platelets at a higher concentration of arachidonic acid, presumably reflecting a decreased ability to reduce the 12-hydroperoxyeicosatetraenoic acid intermediate. These results suggest that the contribution of GSHPx-1 to the cellular antioxidant mechanism under normal animal development and physiological conditions and to the pulmonary defense against hyperoxic insult is very limited. Nevertheless, the potential antioxidant role of this enzyme in protecting cells and animals against the pathogenic effect of reactive oxygen species in other disorders remains to be defined. The knockout mouse model described in this report will also provide a new tool for future study to distinguish the physiological role of this enzyme from other selenium-containing proteins in mammals under normal and disease states.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1997

Mutational analysis of the role of the distal histidine and glutamine residues of prostaglandin-endoperoxide synthase-2 in peroxidase catalysis, hydroperoxide reduction, and cyclooxygenase activation.

Site-directed mutants of prostaglandin-endoperoxide synthase-2 (PGHS-2) with changes in the peroxidase active site were prepared by mutagenesis, expressed in Sf-9 cells, and purified to homogeneity. The distal histidine, His193, was mutated to alanine and the distal glutamine, Gln189, was changed to asparagine, valine, and arginine. The guaiacol peroxidase activities of H193A, Q189V, and Q189R were drastically reduced to levels observed in the absence of protein; only Q189N retained wild-type PGHS-2 (wtPGHS-2) activity. The mechanism of hydroperoxide reduction by the PGHS-2 mutants was investigated using 15-hydroperoxyeicosatetraenoic acid (15-HPETE), a diagnostic probe of hydroperoxide reduction pathways. The hydroperoxide reduction activity of Q189V and Q189R was reduced to that of free Fe(III) protoporphyrin IX levels, whereas Q189N catalyzed more reduction events than wtPGHS-2. The percentage of two-electron reduction events was identical for wtPGHS-2 and Q189N. The number of hydroperoxide reductions catalyzed by H193A was reduced to approximately 60% of wtPGHS-2 activity, but the majority of products were the one-electron reduction products, 15-KETE and epoxyalcohols. Thus, mutation of the distal histidine to alanine leads to a change in the mechanism of hydroperoxide reduction. Reaction of wtPGHS-2, Q189N, and H193A with varying concentrations of 15-HPETE revealed a change in product profile that suggests that 15-HPETE can compete with the reducing substrate for oxidation by the peroxidase higher oxidation state, compound I. The ability of the PGHS-2 proteins to catalyze two-electron hydroperoxide reduction correlated with the activation of cyclooxygenase activity. The reduced ability of H193A to catalyze two-electron hydroperoxide reduction resulted in a substantial lag phase in the cyclooxygenase assay. The addition of 2-methylimidazole chemically reconstituted the two-electron hydroperoxide reduction activity of H193A and abolished the cyclooxygenase lag phase. These observations are consistent with the involvement of the two-electron oxidized peroxidase intermediate, compound I, as the mediator of the activation of the cyclooxygenase of PGHS.

Animals↗
PubMed1997

Overexpression, purification, and characterization of the catalase-peroxidase KatG from Mycobacterium tuberculosis.

Wild-type catalase-peroxidase KatG from Mycobacterium tuberculosis as well as a specific mutant (R463L) frequently found in isoniazid-resistant strains have been overexpressed in Escherichia coli, allowing purification of sufficient quantities of enzyme for physical and kinetic characterization. Optical absorption and EPR spectroscopies indicate that KatG is similar to a growing class of bacterial catalase-peroxidases. Optical and EPR spectra of KatG in the presence of either a strong field or weak field ligand suggest that, like horseradish peroxidase and metmyoglobin, KatG is likely to have a histidine as a proximal ligand. The wild-type enzyme functions as a highly active catalase as well as a broad specificity peroxidase. Wild-type KatG and the R463L mutant of KatG exhibit identical spectroscopic and kinetic properties. Furthermore, both enzymes are equally capable of metabolizing the important antituberculosis drug isoniazid.

Bacterial Proteins↗
PubMed1997

Binding of iodide to Arthromyces ramosus peroxidase investigated with X-ray crystallographic analysis, 1H and 127I NMR spectroscopy, and steady-state kinetics.

The site and characteristics of iodide binding to Arthromyces ramosus peroxidase were examined by x-ray crystallographic analysis, 1H and 127I NMR, and kinetic studies. X-ray analysis of an A. ramosus peroxidase crystal soaked in a KI solution at pH 5.5 showed that a single iodide ion is located at the entrance of the access channel to the distal side of the heme and lies between the two peptide segments, Phe90-Pro91-Ala92 and Ser151-Leu152-Ile153, 12.8 A from the heme iron. The distances between the iodide ion and heme peripheral methyl groups were all more than 10 A. The findings agree with the results obtained with 1H NMR in which the chemical shift and intensity of the methyl groups in the hyperfine shift region of A. ramosus peroxidase were hardly affected by the addition of iodide, unlike the case of horseradish peroxidase. Moreover, 127I NMR and steady-state kinetics showed that the binding of iodide depends on protonation of an amino acid residue with a pKa of about 5.3, which presumably is the distal histidine (His56), 7.8 A away from the iodide ion. The mechanism of electron transfer from the iodide ion to the heme iron is discussed on the basis of these findings.

Crystallography, X-Ray↗
PubMed1999

The structure of an electron transfer complex containing a cytochrome c and a peroxidase.

Efficient biological electron transfer may require a fluid association of redox partners. Two noncrystallographic methods (a new molecular docking program and 1H NMR spectroscopy) have been used to study the electron transfer complex formed between the cytochrome c peroxidase (CCP) of Paracoccus denitrificans and cytochromes c. For the natural redox partner, cytochrome c550, the results are consistent with a complex in which the heme of a single cytochrome lies above the exposed electron-transferring heme of the peroxidase. In contrast, two molecules of the nonphysiological but kinetically competent horse cytochrome bind between the two hemes of the peroxidase. These dramatically different patterns are consistent with a redox active surface on the peroxidase that may accommodate more than one cytochrome and allow lateral mobility.

Animals↗
PubMed1999

Conversion of an engineered potassium-binding site into a calcium-selective site in cytochrome c peroxidase.

We have previously shown that the K(+) site found in ascorbate peroxidase can be successfully engineered into the closely homologous peroxidase, cytochrome c peroxidase (CCP) (Bonagura, C. A. , Sundaramoorthy, M., Pappa, H. S., Patterson, W. R., and Poulos, T. L. (1996) Biochemistry 35, 6107-6115; Bonagura, C. A., Sundaramoorthy, M., Bhaskar, B., and Poulos, T. L. (1999) Biochemistry 38, 5538-5545). All other peroxidases bind Ca(2+) rather than K(+). Using the K(+)-binding CCP mutant (CCPK2) as a template protein, together with observations from structural modeling, mutants were designed that should bind Ca(2+) selectively. The crystal structure of the first generation mutant, CCPCA1, showed that a smaller cation, perhaps Na(+), is bound instead of Ca(2+). This is probably because the full eight-ligand coordination sphere did not form owing to a local disordering of one of the essential cation ligands. Based on these observations, a second mutant, CCPCA2, was designed. The crystal structure showed Ca(2+) binding in the CCPCA2 mutant and a well ordered cation-binding loop with the full complement of eight protein to cation ligands. Because cation binding to the engineered loop results in diminished CCP activity and destabilization of the essential Trp(191) radical as measured by EPR spectroscopy, these measurements can be used as sensitive methods for determining cation-binding selectivity. Both activity and EPR titration studies show that CCPCA2 binds Ca(2+) more effectively than K(+), demonstrating that an iterative protein engineering-based approach is important in switching protein cation selectivity.

Amino Acid Sequence↗
PubMed2004

A distinctive electrocatalytic response from the cytochrome c peroxidase of nitrosomonas europaea.

Here the cytochrome c peroxidase (CcP) from Nitrosomonas europaea is examined using the technique of catalytic protein film voltammetry. Submonolayers of the bacterial diheme enzyme at a pyrolytic graphite edge electrode give catalytic, reductive signals in the presence of the substrate hydrogen peroxide. The resulting waveshapes indicate that CcP is bound non-covalently in a highly active configuration. The native enzyme has been shown to possess two heme groups of low and high potential (L and H, -260 and +450 mV versus hydrogen, respectively), and here we find that the catalytic waves of the N. europaea enzyme have a midpoint potential of >500 mV and a shape that corresponds to a 1-electron process. The signals increase in magnitude with hydrogen peroxide concentration, revealing Michaelis-Menten kinetics and K(m) = 55 microm. The midpoint potentials shift with substrate concentration, indicating the electrochemically active species observed in our data corresponds to a catalytic species. The potentials also shift with respect to pH, and the pH dependence is interpreted in terms of a two pK(a) model for proton binding. Together the data show that the electrochemistry of the N. europaea cytochrome c peroxidase is unlike other peroxidases studied to date, including other bacterial enzymes. This is discussed in terms of a catalytic model for the N. europaea enzyme and compared with other cytochrome c peroxidases.

Cytochrome-c Peroxidase↗
PubMed2001

Bicarbonate enhances peroxidase activity of Cu,Zn-superoxide dismutase. Role of carbonate anion radical and scavenging of carbonate anion radical by metalloporphyrin antioxidant enzyme mimetics.

Much evidence exists for the increased peroxidase activity of copper, zinc superoxide dismutase (SOD1) in oxidant-induced diseases. In this study, we measured the peroxidase activity of SOD1 by monitoring the oxidation of dichlorodihydrofluorescein (DCFH) to dichlorofluorescein (DCF). Bicarbonate dramatically enhanced DCFH oxidation to DCF in a SOD1/H(2)O(2)/DCFH system. Peroxidase activity could be measured at a lower H(2)O(2) concentration ( approximately 1 microm). We propose that DCFH oxidation to DCF is a sensitive index for measuring the peroxidase activity of SOD1 and familial amyotrophic lateral sclerosis SOD1 mutants and that the carbonate radical anion (CO(3)) is responsible for oxidation of DCFH to DCF in the SOD1/H(2)O(2)/bicarbonate system. Bicarbonate enhanced H(2)O(2)-dependent oxidation of DCFH to DCF by spinal cord extracts of transgenic mice expressing SOD1(G93A). The SOD1/H(2)O(2)/HCO(3)(-)-dependent oxidation was mimicked by photolysis of an inorganic cobalt carbonato complex that generates CO(3). Metalloporphyrin antioxidants that are usually considered as SOD1 mimetic or peroxynitrite dismutase effectively scavenged the CO(3) radical. Implications of this reaction as a plausible protective mechanism in inflammatory cellular damage induced by peroxynitrite are discussed.

Amino Acids, Aromatic↗
PubMed2003

Bicarbonate-dependent peroxidase activity of human Cu,Zn-superoxide dismutase induces covalent aggregation of protein: intermediacy of tryptophan-derived oxidation products.

This study addresses the mechanism of covalent aggregation of human Cu,Zn-superoxide dismutase (hSOD1WT) induced by bicarbonate (HCO3-)-mediated peroxidase activity. Higher molecular weight species (apparent dimers and trimers) of hSOD1WT were formed from incubation mixtures containing hSOD1WT, H2O2, and HCO3-. HCO3--dependent peroxidase activity and covalent aggregation of hSOD1WT were mimicked by UV photolysis of hSOD1-WT in the presence of a [Co(NH3)5CO3]+ complex that generates the carbonate radical anion (CO3.). Human SOD1WT has but one aromatic residue, a tryptophan residue (Trp-32) on the surface of the protein. Substitution of Trp-32 with phenylalanine produced a mutant (hSOD1W32F) that exhibits HCO3--dependent peroxidase activity similar to wild-type enzyme. However, unlike hSOD1WT, incubations containing hSOD1W32F,H2O2, and HCO3-did not result in covalent aggregation of SOD1. These findings indicate that Trp-32 is crucial for CO3.-induced covalent aggregation of hSOD1WT. Spin-trapping results revealed the formation of the Trp-32 radical from hSOD1WT, but not from hSOD1W32F. Spin traps also inhibited the covalent aggregation of hSOD1WT. Fluorescence experiments revealed that Trp-32 was further oxidized by CO3., forming kynurenine-type products in the presence of oxygen. Molecular oxygen was needed for HCO3-/H2O2-dependent aggregation of hSOD1WT, implicating a role for a Trp-32-dependent peroxidative reaction in the covalent aggregation of hSOD1WT. Taken together, these results indicate that Trp-32 oxidation is crucial for covalent aggregation of hSOD1. Implications of HCO3--dependent SOD1 peroxidase activity in amyotrophic lateral sclerosis disease are discussed.

Amyotrophic Lateral Sclerosis↗
PubMed2003

Nuclear thiol peroxidase as a functional alkyl-hydroperoxide reductase necessary for stationary phase growth of Saccharomyces cerevisiae.

Yeast nucleus-localized thiol peroxidase (nTPx) was characterized as a functional peroxidase. There are two cysteine residues in nTPx. Replacement of Cys-106 or Cys-111 with serine resulted in a complete loss of thioredoxin-linked peroxidase activity. However, when their activities were measured in terms of the ability to inhibit oxidation of glutamine synthetase, C111S showed the same antioxidant activity as the wild type protein. SDS-PAGE gel analysis revealed that only C111S existed as the dimer form. In addition to the identification of Cys-106 as the primary catalytic site, these data suggest the formation of the intradisulfide bond as a part of the catalytic cycle between nTPx and thioredoxin. nTPx preferentially reduced alkyl-hydroperoxides rather than H2O2. Furthermore, a nTPx mutant strain showed higher sensitivity toward alkyl-hydroperoxide than hydrogen peroxide. Also, reduction of the viability of nTPx mutant strain against various oxidants supports an in vivo antioxidant role for nTPx. nTPx transcriptional activity was not significantly detectable in log phase yeast, but the activity was exponentially increased after the diauxic shift. The transcriptional activity was highly induced even in the log phase yeast grown in nonfermentable carbon source. Deletion of Tor1p, Ras1p, and Ras2p resulted in considerable induction when compared with their parent strains, demonstrating the activation of the transcription of nTPx gene at the diauxic shift. Transcription of nTPx gene was induced in response to oxidative stress. Viability of a stationary phase nTPx mutant was considerably reduced compared with the isogenic strain. Collectively, these data demonstrate that nTPx is a thiol peroxidase family acting as alkyl-hydroperoxide reductase in the nucleus during post-diauxic growth.

Gene Expression Regulation, Fungal↗
PubMed2004

Crystal structure of Mycobacterium tuberculosis catalase-peroxidase.

The Mycobacterium tuberculosis catalase-peroxidase is a multifunctional heme-dependent enzyme that activates the core anti-tuberculosis drug isoniazid. Numerous studies have been undertaken to elucidate the enzyme-dependent mechanism of isoniazid activation, and it is well documented that mutations that reduce activity or inactivate the catalase-peroxidase lead to increased levels of isoniazid resistance in M. tuberculosis. Interpretation of the catalytic activities and the effects of mutations upon the action of the enzyme to date have been limited due to the lack of a three-dimensional structure for this enzyme. In order to provide a more accurate model of the three-dimensional structure of the M. tuberculosis catalase-peroxidase, we have crystallized the enzyme and now report its crystal structure refined to 2.4-A resolution. The structure reveals new information about dimer assembly and provides information about the location of residues that may play a role in catalysis including candidates for protein-based radical formation. Modeling and computational studies suggest that the binding site for isoniazid is located near the delta-meso heme edge rather than in a surface loop structure as currently proposed. The availability of a crystal structure for the M. tuberculosis catalase-peroxidase also permits structural and functional effects of mutations implicated in causing elevated levels of isoniazid resistance in clinical isolates to be interpreted with improved confidence.

Amino Acid Sequence↗
PubMed2005

Kinetics of interconversion of ferrous enzymes, compound II and compound III, of wild-type synechocystis catalase-peroxidase and Y249F: proposal for the catalatic mechanism.

With the exception of catalase-peroxidases, heme peroxidases show no significant ability to oxidize hydrogen peroxide and are trapped and inactivated in the compound III form by H2O2 in the absence of one-electron donors. Interestingly, some KatG variants, which lost the catalatic activity, form compound III easily. Here, we compared the kinetics of interconversion of ferrous enzymes, compound II and compound III of wild-type Synechocystis KatG, the variant Y249F, and horseradish peroxidase (HRP). It is shown that dioxygen binding to ferrous KatG and Y249F is reversible and monophasic with apparent bimolecular rate constants of (1.2 +/- 0.3) x 10(5) M(-1) s(-1) and (1.6 +/- 0.2) x 10(5) M(-1) s(-1) (pH 7, 25 degrees C), similar to HRP. The dissociation constants (KD) of the ferrous-dioxygen were calculated to be 84 microm (wild-type KatG) and 129 microm (Y249F), higher than that in HRP (1.9 microm). Ferrous Y249F and HRP can also heterolytically cleave hydrogen peroxide, forming water and an oxoferryl-type compound II at similar rates ((2.4 +/- 0.3) x 10(5) M(-1) s(-1) and (1.1 +/- 0.2) x 10(5) M(-1) s(-1) (pH 7, 25 degrees C)). Significant differences were observed in the H2O2-mediated conversion of compound II to compound III as well as in the spectral features of compound II. When compared with HRP and other heme peroxidases, in Y249F, this reaction is significantly faster ((1.2 +/- 0.2) x 10(4) M(-1) s(-1))). Ferrous wild-type KatG was also rapidly converted by hydrogen peroxide in a two-phasic reaction via compound II to compound III (approximately 2.0 x 10(5) M(-1) s(-1)), the latter being also efficiently transformed to ferric KatG. These findings are discussed with respect to a proposed mechanism for the catalatic activity.

Amino Acid Substitution↗
PubMed2003

Isoenzymes of peroxidase and esterase related to morphogenesis in Mammillaria gracillis Pfeiff. tissue culture.

In vitro propagated plants of the cactus Mammillaria gracillis Pfeiff. (Cactaceae) spontaneously produced callus. The habituated callus regenerated normal and hyperhydric shoots without the addition of grown regulators. Tumours were obtained by infecting cactus explants with Agrobacterium tumefaciens; the wild strain B6S3 (tumour TW) or with the rooty mutant GV3101 (tumour TR). Both tumour lines grew vigorously, never expressing any morphogenic potential. In this study, cactus shoots, callus, normal and hyperhydric regenerants and TW and TR tumours were compared with regard to peroxidase (EC 1.11.1.7) and esterase activity, and isoenzyme patterns. Guaiacol peroxidase activity was the lowest in the cactus shoots and in the normal regenerants. Callus, hyperhydric regenerants and tumours had peroxidase activity of 6 to 7 times higher. Esterase activity was measured with 1- and 2-naphthylacetate as broad-spectrum substrates. The highest esterase activity was determined in tumours with both substrates. All tissues, except the TR tumour, had higher esterase activity for 2-compared to 1-naphtylacetate. Peroxidase and esterase isoenzyme patterns were not completely identical among the investigated tissues.

Agrobacterium tumefaciens↗
PubMed2001

Two pathogenesis-related peroxidases in greengram (Vigna radiata (L.) wilczek) leaves and cultured cells induced by Macrophomina phaseolina (Tassi) Goid. and its elicitor.

An elicitor has been isolated from Macrophomina phaseolina, the root rot and leaf blight pathogen of greengram. Suspension-cultured cells of greengram were established which responded to the fungal elicitor. When greengram leaves were inoculated with M. phaseolina two new peroxidases appeared. Similarly, two new peroxidases could be detected in suspension-cultured greengram cells when treated with the fungal elicitor. These peroxidases were purified by column chromatography and their molecular masses were 27 and 38 kDa. The new peroxidases detected in both leaves and cultured cells appear to be similar with the same molecular weights.

Basidiomycota↗
PubMed1980

Comparison of glucose oxidase and peroxidase as labels for antibody in enzyme-linked immunosorbent assay.

Horse-radish peroxidase and glucose oxidase were each separately conjugated to identical aliquots of goat IgG containing anti-human IgG antibodies. We used a minor modification of the periodate method of Nakane and Kawaoi to covalently bind each enzyme to IgG. Glucose oxidase conjugates proved superior to peroxidase conjugates based on the following qualities. The glucose oxidase conjugates had 1) usable dilutions 2 to 10 times greater than peroxidase conjugates, 2) much lower background or control non-specific activities, and 3) nearly twice the sensitivity as expressed by absorbance change vs. change in antigen. Comparison of the antibody titers showed the glucose oxidase conjugate with 80% and the peroxidase conjugate with 20% of the original goat antibody.

Animals↗
PubMed1996

Comparison of 5-hydroxy-2, 3-dihydrophthalazine-1, 4-dione and luminol as co-substrates for detection of horseradish peroxidase in enhanced chemiluminescent reactions.

The utility of 5-hydroxy-2, 3-dihydrophthalazine-1, 4-dione (HDP) as a co-substrate for the chemiluminescent detection of horseradish peroxidase was assessed. Several substituted aryl boronic acid derivatives (4-phenyl, 4-iodo) acted as potent enhancers of the peroxidase catalyzed reaction. Addition of chelating agents (EDTA) and surfactants (Tween-20 and [poly (vinylbenzyl)tributylphosphonium chloride-poly (vinylbenzyl) trioctylphosphonium chloride copolymer]) modulated background light emission and the intensity and duration of the signal from both HDP and luminol. However, HDP was found to be inferior to luminol in the peroxidase assay. Comparative studies revealed that at 500 amol of peroxidase the S/B was ten-fold higher using a commercial luminol-based signal reagent as compared with an HDP-EDTA-Tween-20 reagent (S/B t = 0 min 21.8 vs 1.7, S/B t = 10 min 17.8 vs 2.0).

Boronic Acids↗
PubMed1991

Changes in peroxidases associated with radiation-induced sprout inhibition in garlic (Allium satiyum L.).

The effects of an acute dose of gamma-rays (10 Gy) to post-dormant garlic cloves on inner sprout growth and changes in peroxidases and soluble proteins were evaluated up to 100 days of storage in darkness at 19 +/- 1 degree C and 42 +/- 2% relative humidity. Radiation-induced inhibition of sprout growth became evident after 25 days of treatment and was synchronous with a marked increase in peroxidase activity. Thin-layer isoelectric focusing revealed that radiation induced an increase in the number of anodic peroxidase isoenzymes at 100 days, suggesting modifications in the vascularization process. Neither the soluble protein content nor the protein pattern were affected by irradiation. These results are discussed in terms of a possible mediating effect of peroxidase on radiation-induced sprout inhibition in garlic.

Cobalt Radioisotopes↗