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PubMed1991

Chemical and transient state kinetic studies on the formation and decomposition of horseradish peroxidase compounds XI and XII.

Previous studies on the chlorination reaction catalyzed by horseradish peroxidase using chlorite as the source of chlorine detected the formation of a chlorinating intermediate that was termed Compound X (Shahangian, S., and Hager, L.P. (1982) J. Biol. Chem. 257, 11529-11533). These studies indicated that at pH 10.7, the optical absorption spectrum of Compound X was similar to the spectrum of horseradish peroxidase Compound II. Compound X was shown to be quite stable at alkaline pH values. This study was undertaken to examine the relationship between the oxidation state of the iron protoporphyrin IX heme prosthetic group in Compound X and the chemistry of the halogenating intermediate. The experimental results show that the optical absorption properties and the oxidation state of the heme prosthetic group in horseradish peroxidase are not directly related to the presence of the activated chlorine atom in the intermediate. The oxyferryl porphyrin heme group in alkaline Compound X can be reduced to a ferric heme species that still retains the activated chlorine atom. Furthermore, the reaction of chlorite with horseradish peroxidase at acidic pH leads to the secondary formation of a green intermediate that has the spectral properties of horseradish peroxidase Compound I (Theorell, H. (1941) Enzymologia 10, 250-252). The green intermediate also retains the activated chlorine atom. By analogy to peroxidase Compound I chemistry, the heme prosthetic group in the green chlorinating intermediate must be an oxyferryl porphyrin pi-cation radical species (Roberts, J. E., Hoffman, B. M., Rutter, R. J., and Hager, L. P. (1981) J. Am. Chem. Soc. 103, 7654-7656). To be consistent with traditional peroxidase nomenclature, the red alkaline form of Compound X has been renamed Compound XII, and the green acidic form has been named Compound XI. The transfer of chlorine from the chlorinating intermediate to an acceptor molecule follows an electrophilic (rather than a free radical) path. A mechanism for the reaction is proposed in which the activated chlorine atom is bonded to a heteroatom on an active-site amino acid side chain. Transient state kinetic studies show that the initial intermediate, Compound XII, is formed in a very fast reaction. The second-order rate constant for the formation of Compound XII is approximately 1.1 x 10(7) M-1 s-1. The rate of formation of Compound XII is strongly pH-dependent. At pH 9, the second-order rate constant for the formation of Compound XII drops to 1.5 M-1 s-1. At acidic pH values, Compound XII undergoes a spontaneous first-order decay to yield Compound XI.(ABSTRACT TRUNCATED AT 400 WORDS)

Binding Sites↗

PubMed1991

Lignin peroxidase: toward a clarification of its role in vivo.

The extracellular lignin peroxidase from the white-rot basidiomycete Phanerochaete chrysosporium is thought to play an important role in lignin biodegradation. However, the majority of lignin-derived preparations actually experience overall polymerization at the hands of the enzyme in vitro. It has now been found that, in the presence of H2O2 at pH 4.0, the monomeric lignin precursor coniferyl alcohol is polymerized quantitatively by a lignin peroxidase preparation which is uncontaminated with MnII-dependent peroxidases. 13C NMR spectrometry of the resulting dehydropolymerisates from 13C-labeled monolignols confirms that the frequencies of different interunit linkages are very similar to those engendered through the action of horseradish peroxidase with H2O2. Indeed, lignin peroxidase does not ultimately seem to be a prerequisite for lignin degradation in vivo, yet its activity can still accelerate the conversion of lignin-derived preparations by P. chrysosporium to CO2. Consequently, lignin peroxidase can provisionally be expected to fulfill two important functions. On the one hand, the enzyme may detoxify lower molecular weight phenolic compounds released from lignins during their fungal decomposition. On the other hand, through the introduction of suitable functional groups, lignin peroxidase could indirectly enhance the susceptibility of macromolecular lignin structures toward depolymerization by another enzyme.

Basidiomycota↗

PubMed1989

Peroxidase secretion by lacrimal glands from juvenile F344 rats.

Secretion of peroxidase by rat lacrimal glands is generally acknowledged to be greater in juvenile rats than in adults. However, this phenomenon has not been so well documented in lacrimal glands as other age-related changes have been. Therefore, we studied lacrimal protein and peroxidase secretion in response to muscarinic cholinergic and alpha-adrenergic stimulation of glands from 35- to 90-day-old male F344 rats. Lacrimal tissue fragments were incubated in perifusion chambers, and secretion of protein and peroxidase was measured in response to stimulation by carbachol or phenylephrine. There was a negative first-order correlation between total protein secretion and age. Dose-response curves showed that at the highest doses there was a small but significant change in protein secretion. Secretion of lacrimal peroxidase in response to carbachol and phenylephrine changed significantly with increasing age. The tissue content of peroxidase was diminished by about 25% during this period, but that decrease alone was not sufficient to explain the changes in secretory responsiveness. The decrease of peroxidase secretion elicited by phenylephrine had both first- and second-order components in its correlation with age between 35 and 90 days. Dose-response curves for 5-week (35-41-day)- and 12-week (84-90-day)-old tissue showed that the maximum secretion of peroxidase was reduced by about 50%, but with no apparent shift in the dose-response curve.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Phosphorylation of lignin peroxidases from Phanerochaete chrysosporium. Identification of mannose 6-phosphate.

Many of the extracellular lignin-degrading peroxidases from the wood-degrading fungus Phanerochaete chrysosporium are phosphorylated. Immunoprecipitation of the extracellular fluid of cultures grown with H2K32PO4 with a polyclonal antibody raised against one of the lignin peroxidase isozymes, H8 (pI 3.5), revealed the incorporation of H2K32PO4 into lignin peroxidases. Analyses of the purified isozymes from labeled cultures by isoelectric focusing showed that, in addition to isozyme H8, lignin peroxidase isozymes H2 (pI 4.4), H6 (pI 3.7), and H10 (pI 3.3) are also phosphorylated. These analyses also showed that lignin peroxidase isozyme H1 (pI 4.7) and manganese-dependent peroxidase isozymes H3 (pI 4.9) and H4 (pI 4.5) are not phosphorylated. Phosphate quantitation indicated the presence of one molecule of phosphate/molecule of enzyme for all of the phosphorylated isozymes. To locate the site of phosphorylation, one-dimensional phosphoamino acid analysis was performed with hydrolyzed 32P-protein. However, phosphotyrosine, phosphoserine, and phosphothreonine could not be identified. Coupled enzyme assays of acid hydrolysate indicated the presence of mannose 6-phosphate as the phosphorylated component on the lignin peroxidase isozymes. Digestion of the isozymes with N-glycanase released the phosphate component, indicating that the mannose 6-phosphate is contained on an asparagine-linked oligosaccharide.

Agaricales↗

PubMed1989

Manganese-dependent peroxidase from Phanerochaete chrysosporium. Primary structure deduced from cDNA sequence.

A cDNA clone encoding a manganese-dependent peroxidase from the filamentous fungus Phanerochaete chrysosporium was isolated and characterized. The clone, lambda MP-1, was isolated by screening a lambda gt11 expression library with polyclonal antibodies raised against a purified manganese-dependent peroxidase (isozyme H4, pI 4.5). The lambda MP-1 cDNA sequence predicts a mature protein containing 358 amino acids with a molecular weight of 37,711 preceded by a leader peptide of 24 amino acid residues. The N-terminal amino acid sequence of a purified manganese-dependent peroxidase (H4) corresponds to the sequence deduced from the cDNA. Some homology (58% in nucleotide sequence and 65% in amino acid sequence) is observed between the manganese-dependent peroxidase and lignin peroxidase isozyme H8. The highest degree of similarity is observed near the enzyme active site. Residues essential for peroxidase activity, the distal and proximal histidines, can be identified in the amino acid sequence. Near these residues, homology is also observed with several other peroxidases. Northern blot analysis of poly(A)+ RNA from nitrogen-limited P. chrysosporium cultures indicates that the level of messenger RNA correlates with expression of the enzyme and its activity. This is consistent with the regulation of the enzyme being at the level of transcription.

Agaricales↗

PubMedDate not supplied

Comparison of immunohistochemical staining of a mitochondrial protein, lipoamide dehydrogenase, with Fab'-peroxidase conjugates prepared by maleimide or periodate.

IgG-maleimide peroxidase, Fab'-maleimide peroxidase, polymer and monomer types of Fab'-periodate peroxidase were prepared from an antibody against rat lipoamide dehydrogenase, a component of the pyruvate dehydrogenase complex which is located in mitochondria. They were examined for immunohistochemical staining of the rat kidney. Fab'-maleimide peroxidase was the best for staining mitochondrial protein. IgG-maleimide peroxidase and the monomer type of Fab'-periodate peroxidase had the same intensity of staining. The polymer type of Fab'-periodate peroxidase could not stain the lipoamide dehydrogenase.

Animals↗

PubMed1985

Thyroid peroxidase selects the mechanism of either 1- or 2-electron oxidation of phenols, depending on their substituents.

Unlike lactoperoxidase and horseradish peroxidase, thyroid peroxidase catalyzed the oxidation of hydroquinone mostly by way of 2-electron transfer. This conclusion could be derived from three independent experiments: ESR measurements of p-benzosemiquinone, trapping the unpaired electron by cytochrome c, and spectrophotometric analysis of catalytic intermediates of the enzymes. The 1-electron flux for hydroquinone oxidation was found to be 15-19% in the reaction of thyroid peroxidase, while it was nearly 100% in the reactions of lactoperoxidase and horseradish peroxidase. From the spectrophotometric analysis of the catalytic intermediates of enzyme, it was suggested that the mechanism of oxidation catalyzed by thyroid peroxidase changes from a 2-electron to a 1-electron type as the substituents at 2- and 6-positions of phenol become bulky or heavy. On the other hand, the mechanism was invariably a 1-electron type when the oxidation of phenols was catalyzed by lactoperoxidase or horseradish peroxidase. These three peroxidases all catalyzed 1-electron oxidation of ascorbate.

Animals↗

PubMed1988

Ultrastructural quantitation of peroxidase- and elastase-containing granules in human neutrophils.

Previous ultrastructural studies of human neutrophils showed two distinctive granule types, the azurophil (peroxidase-positive) and the specific (peroxidase-negative). By identification of granules with peroxidase activity and those immunopositive for elastase antigen, the authors defined two subpopulations of azurophil granules, one that contained peroxidase activity and no measurable elastase antigen and another that contained elastase antigen associated with a small amount of peroxidase activity. They quantitated the peroxidase-positive as well as the elastase-positive granules in human peripheral blood neutrophils and found an average of 1536 +/- 69 peroxidase-positive granules per neutrophil. Of these, 399 +/- 20 were also elastase-positive. The average elastase concentration per neutrophil was 1.59 pg, and the average concentration per granule was 4 X 10(-3) pg. It is concluded that in normal individuals approximately one-third of the azurophil granules contain elastase antigen. Because neutrophil elastase has been implicated in the pathogenesis of emphysema, quantitation of its distribution within the cell presents an approach that may help define selective azurophil granule release and its relationship to the development of emphysema.

Cytoplasmic Granules↗

PubMed1987

gamma-Butyrobetaine hydroxylase and the protective role of glutathione peroxidase.

The selenoenzyme glutathione peroxidase in the presence of GSH effectively replaced catalase in the in vitro assay for gamma-butyrobetaine hydroxylase. Quantitatively, glutathione peroxidase was an order of magnitude more efficient than catalase, with maximal activity at less than 0.1 microM glutathione peroxidase in a standard reaction. Glutathione peroxidase prevented the loss of gamma-butyrobetaine hydroxylase during preliminary incubation with ferrous ions but without other substrates as well as in the course of the reaction. Regardless of whether glutathione peroxidase or catalase was present in the assay, the ascorbate concentrations needed to achieve half-maximal rates were similar (about 1 mM). Phosphate stimulated the rate of L-carnitine synthesis. Ferrous ion saturation indicated a pronounced effect of phosphate on the maximal velocity of the enzyme-catalyzed reaction, but its mechanism of action remains to be elucidated. Based on the subcellular distribution of gamma-butyrobetaine hydroxylase, catalase, and glutathione peroxidase, the role of glutathione peroxidase assumes importance. However, initial studies indicated that the assayable activity of liver gamma-butyrobetaine hydroxylase and L-carnitine concentrations in liver, blood plasma, and muscle were not significantly altered in selenium-deficient rats.

Animals↗

PubMed1987

Purification and quantitation of a rat plasma selenoprotein distinct from glutathione peroxidase using monoclonal antibodies.

Studies with 75Se have shown the existence of a rat plasma selenoprotein in addition to glutathione peroxidase. Because the function of the protein is not known, it has been referred to as selenoprotein P. A partially purified preparation was used to produce a monoclonal antibody to selenoprotein P. The antibody did not bind glutathione peroxidase as evidenced by its failure to remove glutathione peroxidase activity from rat plasma by immunoprecipitation. An immunoaffinity column was prepared with the monoclonal antibody, and selenoprotein P was purified 1270-fold from rat plasma in a two-step procedure. The purified selenoprotein P migrated in a single band with an Mr of 57,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Autoradiography demonstrated that this band contained 75Se when the protein was purified from rats which had received 75SeO2-(3). A competitive radioimmunoassay for selenoprotein P was developed. The selenoprotein P concentration in plasma of selenium-replete rats was determined with this assay to be 51 +/- 3.7 micrograms/ml. It was less than 5 micrograms/ml in plasma from selenium-deficient rats. Injection of 50 micrograms of selenium into selenium-deficient rats caused an increase in selenoprotein P from less than 10% of control to 52% of control in 6 h. Plasma glutathione peroxidase activity increased only from 2.2 to 3.1% of control. These experiments demonstrate that rat plasma contains a selenoprotein distinct from glutathione peroxidase. The concentration of this selenoprotein is depressed in selenium deficiency, as is glutathione peroxidase activity, but selenoprotein P increases more rapidly when selenium is supplied than does glutathione peroxidase activity.

Animals↗

PubMed1986

18O studies of the peroxidase-catalyzed oxidation of N-methylcarbazole. Mechanisms of carbinolamine and carboxaldehyde formation.

Chloroperoxidase, horseradish peroxidase, hemoglobin, myoglobin, lactoperoxidase, and microperoxidase catalyzed the ethyl hydroperoxide-dependent oxidation of N-methylcarbazole to N-(hydroxymethyl)carbazole and N-formylcarbazole as major products. Mass spectral analysis of the N-(hydroxymethyl)carbazole formed during the peroxidase-catalyzed N-demethylation of N-methylcarbazole in 18O-enriched medium indicated partial incorporation (7.5-25.9%) of solvent water oxygen into the carbinolamine intermediate in all systems investigated, suggesting that the peroxidase active site is partially accessible to solvent water during N-demethylation. In contrast, solvent water oxygen was not incorporated into the N-formylcarbazole formed during the peroxidase-catalyzed oxidation of N-methylcarbazole. N-(Hydroxymethyl)carbazole was not further metabolized by the peroxidases in the presence of ethyl hydroperoxide, indicating that it is not an intermediate in N-formylcarbazole formation. The horseradish peroxidase-catalyzed formation of N-formylcarbazole was decreased by 77% when the hydroperoxide-supported reactions were carried out in a nitrogen atmosphere, while the formation of N-(hydroxymethyl)carbazole was decreased by 46%. When the horseradish peroxidase-catalyzed reactions were carried out in a 18O2 atmosphere, 18O incorporation into N-(hydroxymethyl)carbazole was 64.4% of the total oxygen, while 81.8% of the oxygen incorporated into N-formylcarbazole came from 18O2. These results suggest that there are two different mechanisms for the formation of N-(hydroxymethyl)carbazole, both involving the initial oxidation of N-methylcarbazole to a neutral carbon-centered radical. The radical can be further oxidized in the enzyme active site to an iminium cation, which reacts with water derived from either the oxidant or the medium to form the carbinolamine. Alternatively, the substrate radical can react with molecular oxygen to form a hydroperoxy radical, which decomposes to form the carboxaldehyde and carbinolamine.

Carbazoles↗

PubMedDate not supplied

Peroxidase activity as a marker for estrogenicity: studies in uterus and mammary tumors.

We examined the possibility that peroxidase activity might be a marker for estrogen activity in established estrogen-dependent tissues: dimethylbenz[a]anthracene (DMBA)-induced rat mammary tumors and human breast cancer. In DMBA-induced tumors undergoing regression after ovariectomy or tamoxifen treatment, tumor size decreased by 50%, estradiol receptors (ER) and progesterone receptors (PgR) decreased by 25 and 20%, respectively, but peroxidase activity paradoxically increased six- to sevenfold. In DMBA tumors stimulated by estradiol treatment or by the cessation of tamoxifen administration in intact rats, tumor size increased threefold. ER and PgR increased two- and threefold, respectively, while peroxidase activity decreased 50%. These data indicate an inverse relation between tumor growth, ER and PgR on the one hand, and peroxidase activity on the other. In the human breast cancers there was a significant negative relation between the presence of ER and peroxidase activity. By using a calibrated Sephadex G-100 column it was shown that uterine peroxidase differs in molecular weight from the peroxidase of rat mammary tumors and that of human breast cancer.

Animals↗

PubMed1978

[Uptake of peroxidase by activated nerve cells of the hypothalamus (author's transl)].

After thirst or adrenalectomy followed by dehydration electron microscopy reveals an activation and an increased uptake of peroxidase in the nerve cells of the supraoptic, paraventricular, ventromedial and praemamillar nuclei. The amount of peroxidase which is taken up runs parallel with the activation of the corresponding nerve cells. After rehydratation the activity of the nerve cells and the uptake of peroxidase decrease. The incorporation of the enzyme by the nerve cells differs depending on the region investigated: After thirst peroxidase is taken up especially by the nerve cells of the supraoptic and paraventricular nuclei. After adrenalectomy, however, this is true for the ventromedial and praemamillar nucleus. In the magnocellular nuclei peroxidase is preferentially incorporated by the perikarya, whereas in the parvocellular nuclei the uptake of the enzyme predominates in the dendrites. Within the nerve cells peroxidase is only seen in heterophagic bodies. The ependyma above the paraventricular nucleus takes up peroxidase in low amounts via the cell membrane which borders the III. ventricle; high amounts are incorporated by the lateral and basal plasmalemma.

Animals↗

PubMed1994

The crystal structure of manganese peroxidase from Phanerochaete chrysosporium at 2.06-A resolution.

The crystal structure of manganese peroxidase (MnP) from the lignin-degrading basidiomycetous fungus Phanerochaete chrysosporium has been solved using molecular replacement techniques and refined to R = 0.20 at 2.0 A. The overall structure is similar to that of two other fungal peroxidases, lignin peroxidase from P. chrysosporium and Arthromyces ramosus peroxidase. Like the other fungal peroxidases, MnP has two structural calcium ions. MnP also has two N-acetylglucosamine residues N-linked to Asn131 that are readily visible in the electron density map. The active site, consisting of a proximal His ligand H-bonded to an Asp residue and a distal side peroxide binding pocket consisting of a catalytic His and Arg, is the same as in the aforementioned fungal peroxidases as well as yeast cytochrome c peroxidase. MnP differs in having five rather than four disulfide bonds. The additional disulfide bond, Cys341-Cys348, is located near the C terminus of the polypeptide chain. Importantly, a new cation binding site, which we propose is the manganese-binding site of MnP, was located in the crystal structure. The ligands constituting the Mn(2+)-binding site include Asp179, Glu35, Glu39, a heme propionate, and two water molecules. Electron transfer from Mn2+ to the heme edge or iron center is envisioned to occur through a sigma-bonded pathway along a heme propionate.

Amino Acid Sequence↗

PubMed1998

Mechanisms of dopamine and dobutamine interference in biochemical tests that use peroxide and peroxidase to generate chromophore.

Dopamine and dobutamine have recently been shown to produce a negative interference in several biochemical tests that use peroxide and peroxidase to generate a chromophore. To define the chemical mechanism of this interference, we examined the effects of dopamine and dobutamine in various peroxidase-based biochemical tests. Dopamine interfered stoichiometrically with peroxidase-based tests that use 4-aminophenazone to form chromophore but interfered little in those that use other compounds to generate chromophore. Dopamine reacts with 4-aminophenazone in the presence of peroxide and peroxidase to form a novel quinone-imine dye, with a smaller absorptivity than the chromophore formed in the absence of dopamine. The smaller absorptivity of this novel chromophore results in negative interference by reducing the total absorbance at the wavelength used to measure analyte. In contrast, dobutamine interfered stoichiometrically with all peroxidase-based tests studied, regardless of whether 4-aminophenazone was used to form the chromophore. Dobutamine was rapidly oxidized by peroxide in the presence of peroxidase, thus depleting the peroxide necessary to generate chromophore. Dopamine and dobutamine demonstrate two distinct general mechanisms of interference in peroxidase-based biochemical tests.

Ampyrone↗

PubMed1987

Purification and some properties of peroxidases of rat bone marrow.

Myeloperoxidase and eosinophil peroxidase were separated and purified from rat bone marrow cells using cetyltrimethylammonium bromide as the solubilizer and then with column chromatographies on CM-Sephadex C-50 and Con A-Sepharose. Both purified enzymes were observed to be apparently homogeneous by SDS-polyacrylamide gel electrophoresis. Myeloperoxidase consisted of two subunits of Mr 57,000 and 15,000, and eosinophil peroxidase two of 53,000 and 14,000. On structural analysis of the enzymes, their visual and ESR spectra revealed that the structure surrounding the heme in myeloperoxidase was different from that in eosinophil peroxidase. Moreover, substrate specificity and sensitivity to inhibitors such as azide and cyanide differed between the two enzymes. Rat bone marrow possesses two distinct peroxidases, myeloperoxidase and eosinophil peroxidase, which have different subunits and different heme microenvironments. Therefore, the difference in enzymatic function between the two peroxidases may be due to their structures.

Animals↗

PubMed2002

Eosinophil peroxidase produces hypobromous acid in the airways of stable asthmatics.

Eosinophil peroxidase and myeloperoxidase use hydrogen peroxide to produce hypobromous acid and hypochlorous acid. These powerful oxidants may damage the lungs if they are produced as part of the inflammatory response in asthma. The aim of this study was to determine if peroxidases generate hypohalous acids in the airways of individuals with stable asthma, and if they affect lung function. Sputum was induced from patients with mild to moderate asthma and from healthy controls. Eosinophil peroxidase, myeloperoxidase, chlorinated and brominated tyrosyl residues, and protein carbonyls were measured in sputum supernatants. Eosinophil peroxidase protein was significantly elevated in asthmatic subjects whereas myeloperoxidase protein was not. There was significantly more 3-bromotyrosine (Br-Tyr) in proteins from the sputum of asthmatics compared to controls (0.79 vs. 0.23 mmol Br-Tyr/mol Tyr; medians p < .0001). Levels of 3-chlorotyrosine (0.23 vs. 0.14 mmol Cl-Tyr/mol Tyr; medians p = .11) and protein carbonyls (0.347 vs. 0.339 nmol/mg protein; medians p = .56) were not significantly increased in asthmatics. Levels of 3-bromotyrosine were strongly correlated with eosinophil peroxidase protein (r = 0.79, p < .0001). There were no significant correlations between the markers of oxidative stress and lung function. We conclude that eosinophil peroxidase produces substantial amounts of hypobromous acid in the airways of stable asthmatics. Although this highly reactive oxidant is a strong candidate for exacerbating inflammatory tissue damage in the lung, its role in asthma remains uncertain.

Adult↗

PubMed2003

A biochemical and molecular characterization of LEP1, an extensin peroxidase from lupin.

An analysis of apoplastic extensin cross-linking activity in vegetative organs of Lupinus albus indicated that leaves contained the highest specific activity. Assays of peroxidases fractionated from this material demonstrated that this activity could be largely attributed to a soluble and apoplastic 51-kDa peroxidase, denoted LEP1. Relative to other purified peroxidases, LEP1 demonstrates high extensin cross-linking activity and can be classified as an extensin peroxidase (EP). Optimal conditions for the in vitro oxidation of other phenolic substrates included 1.5-3.0 mm peroxide at pH 5.0. EP activity of LEP1 was low under these conditions but optimal and substantially higher with 100 microm peroxide and neutral pH, suggesting that physiological changes in pH and peroxide in muro could heavily influence the extensin cross-linking activity of LEP1 in vivo. Analysis of LEP1 glycans indicated 11-12 N-linked glycans, predominantly the heptasaccharide Man3XylFucGlcNAc2, but also larger structures showing substantial heterogeneity. Comparative assays with horseradish peroxidase isoform C and peanut peroxidases suggested the high level of glycosylation in LEP1 may be responsible for the high solubility of this EP in the apoplastic space. A full-length cDNA corresponding to LEP1 was cloned. Quantitative reverse transcriptase-PCR demonstrated LEP1 induction in apical portions of etiolated hypocotyls 30-60 min after exposure to white light, prior to the onset of growth inhibition. Comparative modeling of the translated sequence indicated an unusually unobstructed equatorial cleft across the substrate access channel, which might facilitate interaction with extensin and confer higher EP activity.

Amino Acid Sequence↗