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PubMed1995

Phagocytosis and H2O2 induce catalase and metallothionein gene expression in human retinal pigment epithelial cells.

PURPOSE: Reactive oxygen intermediates have been implicated in the aging process and degenerative diseases of the eye, including retinopathy of prematurity, cataractogenesis, and macular degeneration. The purpose of this study was to investigate the effect of phagocytosis of photoreceptor outer segments and the addition of exogenous H2O2 on catalase and metallothionein expression in human retinal pigment epithelial cells. METHODS: Confluent RPE cells were treated with bovine photoreceptor outer segments or H2O2 for either 6 or 18 hours. Slot blot hybridization was used to assess catalase and metallothionein gene expression after 6 hours. Catalase enzyme activity and metallothionein content were measured after 18 hours. RESULTS: Phagocytosis or the addition of H2O2 increased catalase enzyme activity and metallothionein twofold above control levels. The addition of n-acetyl cysteine abrogated the inductive effect caused by either stress. Catalase and metallothionein gene expression, measured by slot blot hybridization, also were measurably induced by either stress. Phagocytosis of photoreceptor outer segments increased extracellular H2O2 concentration nine times above control. CONCLUSIONS: The response of the retinal pigment epithelial cells to phagocytosis was indistinguishable from the response observed after the addition of exogenous H2O2. The generation of H2O2 during phagocytosis may act as an intracellular signal in retinal pigment epithelial cells that leads to increased levels of key antioxidant enzymes and other proteins important for protecting the cells from oxidative damage.

Adolescent↗
PubMed1995

Immunogold labelling indicates high catalase concentrations in amorphous and crystalline inclusions of sunflower (Helianthus annuus L.) peroxisomes.

Immunogold labelling and electron microscopy were used to investigate whether catalase was present in peroxisomal inclusions, the composition of which has not yet been determined in plant cells. In the mesophyll cells of sunflower (Helianthus annuus L.) cotyledons, the catalase gold label was confined to peroxisomes. At day 2 of postgerminative growth in darkness, peroxisomes were free of inclusions, and the matrix was homogeneously labelled with gold particles. Thereafter, amorphous inclusions appeared, but by day 5 of growth, conspicuous crystalline inclusions (cores) were the predominant type. This developmental change, first observed in cotyledons grown in continuous light between day 2.5 and 5, also took place in cotyledons kept in permanent darkness. Both amorphous and crystalline inclusions showed a much higher immunogold label than did the peroxisomal matrix, indicating that catalase was a component of both types of peroxisomal inclusions. In contrast to catalase, the immunogold label of glycolate oxidase was almost completely absent from cores and was confined to the peroxisomal matrix. Together with reports on the absence of other enzymes from peroxisomal inclusions in sunflower and other species (Vaughn, 1989) our results suggest that catalase is a major constituent of amorphous and crystalline peroxisomal inclusions in plants.

Catalase↗
PubMed1993

4-Methylpyrazole inhibits fatty acyl coenzyme synthetase and diminishes catalase-dependent alcohol metabolism: has the contribution of alcohol dehydrogenase to alcohol metabolism been previously overestimated?

Alcohol dehydrogenase (ADH)-deficient deer mice were used as an animal model to investigate the effect of 4-methylpyrazole on alcohol metabolism. After intraperitoneal dosing of these mutant mice with 4-methylpyrazole, rates of ethanol and methanol metabolism in vivo were decreased significantly, by 41% and 35%, respectively. In perfused liver, rates of ethanol metabolism were also decreased up to 61% by 100 microM 4-methylpyrazole. Further, when livers were perfused with methanol, a selective substrate for catalase, rates of methanol metabolism were decreased by 64% by 4-methylpyrazole. It was further determined that 4-methylpyrazole administration caused negligible changes in total hepatic catalase activity and in rates of oxidation of ethanol by isolated microsomes; rather, it acts on catalase-dependent alcohol metabolism by limiting the supply of H2O2. In this study, 4-methylpyrazole inhibited fatty acyl CoA synthetase competitively in liver homogenates. Fatty acyl CoA synthetase is a key enzyme involved in the supply of substrate for peroxisomal oxidation of alcohols via catalase-H2O2. When palmitate was studied, rates of formaldehyde production from methanol were reduced competitively by 4-methylpyrazole; however, when the product palmitoyl CoA was used, the addition of 4-methylpyrazole did not alter activity. 4-Methylpyrazole also inhibited fatty acyl CoA synthetase activity measured directly from CoA disappearance. These data indicate that fatty acyl CoA synthetase is inhibited by 4-methylpyrazole, thus reducing the availability of H2O2 for catalase-dependent alcohol metabolism. Inhibition of methanol metabolism in deer mice expressing ADH indicates that this phenomenon also occurs in species with ADH. Taken together, these data support the hypothesis that the contribution of ADH to alcohol metabolism may have been previously overestimated.

Alcohol Dehydrogenase↗
PubMed1993

[Effect of catalase on acute experimental pancreatitis in rats].

Oxygen free radicals are highly toxic end products of the cellular oxidative metabolism that are scavenged by antioxidative systems such as superoxide dismutase and catalase. Previous studies have suggested that oxygen free radicals may play a role in the pathophysiology of acute pancreatitis. The present study was designed to determine the effect of catalase on experimental acute pancreatitis in the rat. Rats were given either saline or enterokinase by the intraductal pancreatic route. Catalase was given intraperitoneally at doses of 80, 160 and 320 mg/kg. Administration of saline resulted in mild acute pancreatitis. In contrast, administration of enterokinase resulted in oedema, haemorrhage and necrosis of the pancreas. Catalase had no effect when given at 80 mg/kg; at 160 mg/kg, an improvement at the ultrastructural level was noted, whereas at 320 mg/kg, a change in serum calcium level was found. Our studies suggest that intraperitoneal administration of catalase slightly improves the outcome of experimental acute pancreatitis in the rat.

Acute Disease↗
PubMed1995

A cytophotometric and electron-microscopical study on catalase activity in serial cryostat sections of rat liver.

The validity of the histochemical procedure for demonstrating catalase activity in cryostat sections of rat liver at the light- and electron-microscopical level was studied cytophotometrically. Incubations in the presence of 5 mM diaminobenzidine, 44 mM hydrogen peroxide and 2% polyvinyl alcohol performed on fixed cryostat sections resulted in the highest amounts of final reaction product precipitated in a fine granular form which was specific for catalase activity. Serial sections processed for electron microscopy indicated that the osmiophilic final reaction product was exclusively localized in the matrix and core of peroxisomes. The relationship between incubation time and the amounts of final reaction product generated by catalase activity as measured at 460 nm in mid-zonal areas of liver lobules showed non-linearity for the test-minus-control reaction because first-order inactivation of the enzyme occurred during incubation. Linearity of the test-minus-control reaction and section thickness was observed up to 8 microns. Catalase in rat liver showed a Km value of 2.0 mM for its substrate hydrogen peroxide when the diaminobenzidine concentration was 5 mM. It is concluded that the procedure for demonstrating catalase activity in serial cryostat sections of rat liver at the light- and electron-microscopical level is specific and can be applied to quantitative purposes. This approach may be useful in pathology, when only small biopsies are available, when the tissue is heterogeneous, and when other histochemical markers also need to be studied in the same material.

Animals↗
PubMed1996

Regional differences in the distribution of catalase in the epithelium of the ocular lens.

Oxidative stress is thought to play a major role in cataract formation. The present experiments are aimed at gaining a better understanding of the systems that protect the lens from damage by reactive oxygen species. The aqueous humor normally contains hydrogen peroxide (H2O2), a compound capable of generating reactive oxygen species. The systems protecting the ocular lens from oxidative damage are primarily confined to the epithelium, a single layer of cells on the anterior side of the organ directly beneath the lens capsule. When cultured rabbit lenses were challenged with a single dose of 0.2 mM H2O2, cells in the peripheral region of the epithelium survived; those in the central region died. Here we investigate the histochemical and immunoperoxidase distributions of catalase, an enzyme which detoxifies H2O2, in cells from the peripheral and central regions of the epithelium on flat mount preparations of the epithelium. In a flat mount, the entire population of lens epithelial cells can be viewed on one preparation. The reaction product for catalase activity and its immunoperoxidase localization were more intense in peripheral epithelial cells than in cells throughout the central epithelium. Treatment of cultured lens epithelial cells or rabbit lenses with 3-aminotriazole or potassium cyanide, inhibitors of catalase, reduced or abolished the histochemical reaction product. Ultrastructural cytochemistry confirmed the presence of catalase in microperoxisomes of the epithelial cells from whole lenses. The decreased level of catalase throughout the central epithelium may account for the increased susceptibility of these cells to H2O2-induced cell death.

Animals↗
PubMedDate not supplied

[Optimizing synthesis of conjugates of superoxide dismutase and catalase with aldehyde dextrans in surfactant microemulsions in heptane].

Stable microemulsions in heptane retaining considerable amounts of the polar phase were obtained by using Aerosol OT (AOT), Triton X-45, and catalase. Conjugates of superoxide dismutase (SOD) and catalase with aldehyde dextrans (AD) were synthesized in surfactant microemulsions in heptane. Effects of the reaction duration, the microemulsion polar phase volume, and concentrations of enzymes and modifiers on the properties of these conjugates were studied. The catalytic properties of conjugates depended on the nature of the surfactants used to stabilize the microemulsions, the initial concentration of protein in the reaction mixture, and the enzyme: modifier ratio. The degree of modification of the enzymes and the stabilities of their conjugates during isolation from microemulsions by a water-acetone solution depended on the concentration of the AD used. The catalytic properties of the conjugates synthesized were compared, and their stabilities in the presence of H2O2 were described. We suggested a simple method of transformation of whole kinetic curves of H2O2 conversion in coordinates 1/ln([H2O2]0/[H2O2]t - 1/t for simultaneous measurement of the constant of the catalase inactivation rate by H2O2 (Cin, S-1) and the rate constant of the catalase complex 1 interaction with the second H2O2 molecule (C2, M-1 S-1). This method was tested experimentally. Values C2 and Cin for catalase and its conjugates with ADs were compared, and these results were discussed.

Catalase↗
PubMed1998

[Complete amino acid sequence of catalase from the fungus Penicillium vitale].

The polypeptide sequence of the unmodified catalase from Penicillium vitale containing 696 amino acid residues was deduced. The sequences of 76 tryptic peptides of the unmodified catalase, 63 tryptic peptides of the catalase with modified Lys residues, 48 peptides resulting from catalase cleavage by the Staphylococcus aureus V8 protease, and 9 fragments obtained by BrCN-treatment were considered, and a comparison with the sequences of other catalases was made.

Amino Acid Sequence↗
PubMedDate not supplied

[Catalase inactivation during storage in solution and its stabilization by polysaccharides of microbial origin].

It has been experimentally shown that the rate of inactivation of pure catalase in solution does not obey the kinetics of the first order. The kinetics of denaturation taking into account partial stabilization of catalase due to the formation of intermolecular complexes of native molecules with denatured molecules has been derived. Using the equation, the rate of catalase inativation during storage in pure solutions has been calculated from the experimental data. Polysaccharides of microbial origin can also stabilize catalase. The kinetics of catalase inactivation in the system where the enzyme and polysaccharide forms a reversibly dissociating complex has been described.

Catalase↗
PubMed1995

Enrichment in Fraser broth supplemented with catalase or Oxyrase, combined with the microcolony immunoblot technique, for detecting heat-injured Listeria monocytogenes in foods.

The microcolony immunoblot technique using monoclonal antibodies to Listeria monocytogenes was evaluated for its suitability to detect heat-injured cells. Pasteurized milk and filtrates of homogenized raw ground beef slurry and cabbage were inoculated with L. monocytogenes Scott A, heated, diluted, inoculated into Fraser broth (FB) supplemented with 400 micrograms of catalase ml-1 or 0.01 unit of Oxyrase ml-1, and incubated at 30 degrees C for 6 h. Three inoculum populations (high, medium, and low) were used. The extent of injury was dependent on the heating menstruum. Forty percent of the cells were injured in beef slurry filtrate, whereas 79 and 94% were injured in milk and cabbage filtrate, respectively, when foods were heated at 52 degrees C for 20 min. Populations of viable cells were determined using the immunoblot technique and by surface plating on modified Oxford (mMOX) agar. Recovery of cells from heated foods was enhanced in FB supplemented with catalase or Oxyrase compared to recovery in control broth. Essentially all unheated (control) cells could be detected within about 30 h using enrichment and the immunoblot technique; 54 h were required to easily detect colonies on mMOX. In most cases, the number of cells detected in heated milk or filtrates of homogenized beef after enrichment in FB supplemented with catalase or Oxyrase was significantly higher than populations detected using unsupplemented FB; however, enrichment in FB supplemented with catalase or Oxyrase did not significantly increase cell populations in heated cabbage filtrate. Within each heat treatment and level of inoculum, cell populations detected on mMOX agar after incubating plates for 48 h or on immunoblots after 24 h were not significantly different. Results indicate that the immunoblot technique in conjunction with enrichment in FB containing either catalase or Oxyrase can be successfully used to detect healthy and heat-injured cells of L. monocytogenes in diverse types of foods within 34 h.

Animals↗
PubMed2004

Two extracellular proteins with alkaline peroxidase activity, a novel cytochrome c and a catalase-peroxidase, from Bacillus sp. No.13.

A novel cytochrome c and a catalase-peroxidase with alkaline peroxidase activity were purified from the culture supernatant of Bacillus sp. No.13 and characterized. The cytochrome c exhibited absorption maxima at 408 nm (Soret band) in its oxidized state, and 550 (alpha-band), 521 (beta-band), and 415 (Soret band) nm in its reduced state. The native cytochrome c with a relative molecular mass of 15,000 was composed of two identical subunits. The cytochrome c showed over 50 times higher peroxidase activity than those of known c-type cytochromes from various sources. The optimum pH and temperature of the peroxidase activity were about 10.0 and 70 degrees C, respectively. The peroxidase activity is stable in the pH range of 6.0 to 10.8 (30 degrees C, 1-h treatment), and at temperatures up to 80 degrees C (pH 8.5, 20-min treatment). The heme content was determined to be 1 heme per subunit. The amino acid sequence of the cytochrome c showed high homology with those of the c-type cytochromes from Bacillus subtilis and Bacillus sp. PS3. The catalase-peroxidase showed high catalase activity and considerable peroxidase activity, the specific activities being 55,000 and 0.94 micromol/min/mg, respectively. The optimum pH and temperature of the peroxidase activity were in the range of 6.4 to 10.1 and 60 degrees C, respectively. The catalase-peroxidase showed a lower K(m) value (0.67 mM) as to H(2)O(2) than known catalase-peroxidases.

Amino Acid Sequence↗
PubMed2000

Nucleotide sequence analysis, overexpression in Escherichia coli and kinetic characterization of Anacystis nidulans catalase-peroxidase.

Bifunctional catalase-peroxidases are the least understood type of peroxidases. A high-level expression in Escherichia coli of a fully active recombinant form of a catalase-peroxidase (KatG) from the cyanobacterium Anacystis nidulans (Synechococcus PCC 6301) is reported. Since both physical and kinetic characterization revealed its identity with the wild-type protein, the large quantities of recombinant KatG allowed the examination of both the spectral characteristics and the reactivity of its redox intermediates by using the multi-mixing stopped-flow technique. The homodimeric acidic protein (pI = 4.6) contained high catalase activity (apparent K(m) = 4.8 mM and apparent k(cat) = 8850 s(-1)). Cyanide is shown to be an effective inhibitor of the catalase reaction. The second-order rate constant for cyanide binding to the ferric protein is (6.9 +/- 0.2) x 10(5) M(-1 )s(-1) at pH 7.0 and 15 degrees C and the dissociation constant of the cyanide complex is 17 microM. Because of the overwhelming catalase activity, peroxoacetic acid has been used for compound I formation. The apparent second-order rate constant for formation of compound I from the ferric enzyme and peroxoacetic acid is (1.3 +/- 0.3) x 10(4 )M(-1 )s(-1) at pH 7.0 and 15 degrees C. The spectrum of compound I is characterized by about 40% hypochromicity, a Soret region at 406 nm, and isosbestic points between the native enzyme and compound I at 355 and 428 nm. Rate constants for reduction of KatG compound I by o-dianisidine, pyrogallol, aniline and isoniazid are shown to be (7.3 +/- 0.4) x 10(6) M(-1 )s(-1), (5.4 +/- 0.3) x 10(5) M(-1 )s(-1), (1.6 +/- 0.3) x 10(5) M(-1 )s(-1) and (4.3 +/- 0.2) x 10(4) M(-1 )s(-1), respectively. The redox intermediate formed upon reduction of compound I did not exhibit the classical red-shifted peroxidase compound II spectrum which characterizes the presence of a ferryl oxygen species. Its spectral features indicate that the single oxidizing equivalent in KatG compound II is contained on an amino acid which is not electronically coupled to the heme.

Amino Acid Sequence↗
PubMed2004

The role of a bifunctional catalase-peroxidase KatA in protection of Agrobacterium tumefaciens from menadione toxicity.

Agrobacterium tumefaciens is an aerobic plant pathogenic bacterium that is exposed to reactive oxygen species produced either as by-products of aerobic metabolism or by the defense systems of host plants. The physiological function of the bifunctional catalase-peroxidase (KatA) in the protection of A. tumefaciens from reactive oxygen species other than H(2)O(2) was evaluated in the katA mutant (PB102). Unexpectedly, PB102 was highly sensitive to the superoxide generator menadione. The expression of katA from a plasmid vector complemented the menadione-hypersensitive phenotype. A. tumefaciens possesses an additional catalase gene, a monofunctional catalase encoded by catE. Neither inactivation nor high-level expression of the catE gene altered the menadione resistance level. Moreover, heterologous expression of the catalase-peroxidase-encoding gene katG from Burkholderia pseudomallei, but not the monofunctional catalase gene katE from Xanthomonas campestris could restore normal levels of menadione resistance to PB102. A recent observation suggests that the menadione resistance phenotype involves increased activities of organic peroxide-metabolizing enzymes. Heterologous expression of X. campestris alkyl hydroperoxide reductase from a plasmid vector failed to complement the menadione-sensitive phenotype of PB102. The level of menadione resistance shows a direct correlation with the level of peroxidase activity of KatA. This is a novel role for KatA and suggests that resistance to menadione toxicity is mediated by a new, and as yet unknown, mechanism in A. tumefaciens.

Agrobacterium tumefaciens↗
PubMed2001

Improved human sperm recovery using superoxide dismutase and catalase supplementation in semen cryopreservation procedure.

The aim of this work was to evaluate the effects of ROS scavenger supplementation in human semen samples undergoing cryopreservation procedures.After screening out andrological pathologies, we selected 25 male partners of infertile couples with the following semen profile: volume >/= 2.0 ml, normal viscosity, sperm count >/=20 x 10(6)/ml, straight progressive motility (classes 1 and 2) >/= 40% (Mazzilli, Rossi, Delfino and Nofroni (1999) Andrologia 31: 187-194), atypical forms </= 70%, WBCs < 1.0 times 10(6)/ml.After liquefaction, standard semen analysis and the Hypoosmotic Viability Test (HVT) were carried out; the samples were then divided into 4 aliquots. The first was untreated as a control; 200 U/ml of superoxide dismutase (SOD) was added to the second, 200 U/ml of catalase to the third and both SOD (100 U/ml) and catalase (100 U/ml) were added to the fourth aliquot. Each aliquot was mixed (v/v) with TEST yolk buffer freezing medium (Irvine Scientific) and then frozen at -196 degrees C. The percent recovery of progressive motile and swollen spermatozoa was evaluated after thawing.No significant variation in the recovery of progressive motility was seen in the aliquots with added SOD or catalase alone, compared to the control group. On the other hand, a significant improvement in sperm parameter recovery was seen in the aliquot with both SOD and catalase supplementation; perhaps because of their combined and simultaneous action on superoxide anion and hydrogen peroxide. These results suggest that, in some selected cases, SOD and catalase supplementation can contribute greatly to the prevention of sperm membrane lipid peroxidation by ROS and thus allow good sperm parameter recovery after freezing-thawing procedures.

Journal Article↗
PubMed1967

The oxidation of lysine and oxalysine by Mytilus edulis: Identification of the products formed in the presence and the absence of catalase.

1. O-(2-Aminoethyl)serine (oxalysine) was shown to be a substrate of the l-amino acid oxidase of the digestive gland of the common mussel, Mytilus edulis. 2. Three atoms of oxygen were consumed per mole of oxalysine oxidized in the presence of catalase; l-lysine under the same conditions consumed only one atom. 3. The products of oxidation of oxalysine in the presence and the absence of catalase were: ethanolamine, N-oxalylethanolamine and 3-morpholone (the oxygen analogue of 2-piperidone). After acid hydrolysis 70% of the oxalysine oxidized was recovered as ethanolamine. 4. In the absence of catalase 2-aminoethoxyacetic acid was also detected. 5. The products identified account quantitatively for the oxalysine oxidized and for the oxygen uptake. 6. N-Oxalylethanolamine and 2-aminoethoxyacetic acid have been synthesized. 7. Treatment of extracts of the digestive gland at pH3.0 completely inactivated the catalase, leaving the l-amino acid oxidase unaffected. 8. The major product of the oxidation of lysine in the absence of catalase was 2-piperidone.

Journal Article↗
PubMed2004

Influence of the unusual covalent adduct on the kinetics and formation of radical intermediates in synechocystis catalase peroxidase: a stopped-flow and EPR characterization of the MET275, TYR249, and ARG439 variants.

Catalase-peroxidases (KatGs) are heme peroxidases with a catalatic activity comparable to monofunctional catalases. They contain an unusual covalent distal side adduct with the side chains of Trp(122), Tyr(249), and Met(275) (Synechocysis KatG numbering). The known crystal structures suggest that Tyr(249) and Met(275) could be within hydrogen-bonding distance to Arg(439). To investigate the role of this peculiar adduct, the variants Y249F, M275I, R439A, and R439N were investigated by electronic absorption, steady-state and transient-state kinetic techniques and EPR spectroscopy combined with deuterium labeling. Exchange of these conserved residues exhibited dramatic consequences on the bifunctional activity of this peroxidase. The turnover numbers of catalase activity of M275I, Y249F, R439A, and R439N are 0.6, 0.17, 4.9, and 3.14% of wild-type activity, respectively. By contrast, the peroxidase activity was unaffected or even enhanced, in particular for the M275I variant. As shown by mass spectrometry and EPR spectra, the KatG typical adduct is intact in both Arg(439) variants, as is the case of the wild-type enzyme, whereas in the M275I variant the covalent link exists only between Tyr(249) and Trp(122). In the Y249F variant, the link is absent. EPR studies showed that the radical species formed upon reaction of the Y249F and R439A/N variants with peroxoacetic acid are the oxoferryl-porphyrin radical, the tryptophanyl and the tyrosyl radicals, as in the wild-type enzyme. The dramatic loss in catalase activity of the Y249F variant allowed the comparison of the radical species formed with hydrogen peroxide and peroxoacetic acid. The EPR data strongly suggest that the sequence of intermediates formed in the absence of a one electron donor substrate, is por(.-)(+) --> Trp(.-) (or Trp(.-)(+)) --> Tyr(.-). The M275I variant did not form the Trp(.-) species because of the dramatic changes on the heme distal side, most probably induced by the repositioning of the remaining Trp(122)-Tyr(249) adduct. The results are discussed with respect to the bifunctional activity of catalase-peroxidases.

Bacterial Proteins↗
PubMed1996

Cloning, sequencing and disruption of a bromoperoxidase-catalase gene in Streptomyces venezuelae: evidence that it is not required for chlorination in chloramphenicol biosynthesis.

Genomic DNA libraries of Streptomyces venezuelae ISP5230 and of a mutant blocked at the chlorination step of chloramphenicol biosynthesis were probed by hybridization with a synthetic oligonucleotide corresponding to the N-terminal amino acid sequence of a bromoperoxidase-catalase purified from the wild-type strain. Hybridizing fragments obtained from the two strains were cloned and sequenced. Analysis of the nucleotide sequences demonstrated that the fragments contained the same 1449 bp open reading frame with no differences in nucleotide sequence. The deduced polypeptide encoded 483 amino acids with a calculated M(r) of 54,200; the N-terminal sequence was identical to that of the bromoperoxidase-catalase purified from wild-type S. venezuelae. Comparison of the amino acid sequence predicted for the cloned bromoperoxidase-catalase gene (bca) with database protein sequences showed a significant similarity to a group of prokaryotic and eukaryotic catalases, but none to other peroxidases or haloperoxidases. Replacement of the bca gene in the wild-type strain of S. venezuelae with a copy disrupted by insertion of a DNA fragment encoding apramycin resistance did not prevent chloramphenicol production. The results suggest that the role of the enzyme in S. venezuelae is related to its activity as a catalase rather than as a halogenating agent.

Amino Acid Sequence↗
PubMed1978

Apparent Catalase Synthesis in Sunflower Cotyledons during the Change in Microbody Function: A Mathematical Approach for the Quantitative Evaluation of Density-labeling Data.

Density-labeling with 10 mm K(15)NO(3)/70% (2)H(2)O has been used to investigate catalase synthesis in different developmental stages of sunflower (Helianthus annuus L.) cotyledons. A mathematical approach is introduced for the quantitative evaluation of the density-labeling data. The method allows, in the presence of preexisting enzyme activity, calculation of this synthesized activity (apparent enzyme synthesis) which results from the balance between actual enzyme synthesis and the degradation of newly synthesized enzyme at a given time. During greening of the cotyledons, when the catalase activity declines and the population of leaf peroxisomes is formed, the apparent catalase synthesis is lower than, or at best equal to, that occurring during a developmental stage when the leaf peroxisome population is established and catalase synthesis and degradation of total catalase are in equilibrium. This result suggests a formation, in fatty cotyledons, of the leaf peroxisomes by transformation of the glyoxysomes rather than by de novo synthesis.

Journal Article↗