Gene Ontology annotation through association of InterPro records with GO terms
Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity
Annotation inferences using phylogenetic trees
Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
Automatic assignment of GO terms using logical inference, based on on inter-ontology links
Automatic Gene Ontology annotation based on Rhea mapping
Combined Automated Annotation using Multiple IEA Methods
Lactoperoxidase and human airway host defense.
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Normal human airway secretions contain catalytically active LPO, with LPO expression localized to bronchial submucosal glands.
"The data showed that normal human airway secretions contained LPO enzyme activity (0.65 +/- 0.09 microg/mg secreted protein; n = 17), and Western blots of secretions demonstrated bands of the expected sizes for LPO."
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The human airway LPO system uses physiologic thiocyanate and has LPO-dependent antibacterial activity against several airway pathogens.
"Finally, as expected based on the known antibacterial spectrum of the LPO system, airway secretions showed LPO-dependent activity against Pseudomonas aeruginosa."
Molecular heterogeneity and alternative splicing of human lactoperoxidase.
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Human LPO produces multiple splice forms that retain the secretion signal while differing in propeptide-encoding exons.
"Two mRNAs omit propeptide encoding exons while retaining the 5' exon encoding the secretion signal, consistent with the heterogeneity and suggesting a possible functional role for the propeptide."
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Recombinant human LPO V1 and propeptide-skipping V3 are both secreted and catalytically active in the insect-cell expression system.
"Both variants were secreted and were active although V1 was completely processed (see below)."
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Human salivary LPO includes a larger, at least partially unprocessed proLPO form.
"These data showed that a significant portion of immunoreactive LPO in secretions contains the exon 4-peptide and thus was at least partially unprocessed, in contrast to the reported N-termini for human LPO from milk determined by Edman degradation [14]."
Proteomic analysis of human parotid gland exosomes by multidimensional protein identification technology (MudPIT).
Salivary protein profiles are linked to bitter taste acceptance in infants.
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LPO-containing salivary protein bands were detected in infant saliva and associated with greater bitter-solution acceptance, without establishing a direct LPO mechanism.
"while higher abundance of bands containing lactoperoxidase, prolactin-inducible protein and S-type cystatins was associated to a higher bitterness acceptance."
The peroxidation of thiocyanate catalysed by myeloperoxidase and lactoperoxidase.
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LPO catalyzes thiocyanate oxidation to hypothiocyanite with strong dependence on pH and substrate concentrations.
"Peroxidation of SCN- to OSCN-, catalysed by myeloperoxidase and lactoperoxidase, was studied."
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Thiocyanate can competitively inhibit LPO with respect to hydrogen peroxide under acidic conditions, bounding simple substrate models.
"At low pH values, both SCN- and H+ inhibited myeloperoxidase and lactoperoxidase competitively with respect to H2O2."
Cloning and sequence analysis of the human salivary peroxidase-encoding cDNA.
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A human salivary peroxidase/LPO cDNA encodes an approximately 67-kDa unglycosylated translation product.
"In a rabbit reticulocyte lysate transcription/translation system, the cDNA produces a major protein of approx. 67 kDa, which corresponds to the calculated molecular weight of unglycosylated hSPO."
Autocatalytic processing of heme by lactoperoxidase produces the native protein-bound prosthetic group.
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Hydrogen peroxide drives autocatalytic heme modification and covalent attachment in recombinant LPO.
"Reaction of the purified heme. apoLPO complex with H2O2 results in both autocatalytic modification of the heme and covalent attachment to the protein."
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Covalent heme attachment increases LPO peroxidative activity.
"The peroxidative activity of LPO increases in proportion to the extent of covalently bound heme."
Lactoperoxidase-catalyzed oxidation of thiocyanate by hydrogen peroxide: 15N nuclear magnetic resonance and optical spectral studies.
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Hypothiocyanite formation is a principal, condition-dependent product of the LPO/thiocyanate/hydrogen-peroxide system.
"The formation of hypothiocyanite ion (OSCN-) as one of the oxidation products correlated well with the activity of the LPO/SCN-/H2O2 system and was maximum when the concentrations of the H2O2 and SCN- were nearly the same and the pH was less than 6.0."
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Thiocyanate binding is required for oxidation and is lost at alkaline pH.
"Since thiocyanate does not bind to LPO above this pH, the binding of thiocyanate to LPO is considered to be prerequisite for the oxidation of thiocyanate."
Different molecular forms of human salivary lactoperoxidase.
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Human salivary LPO was observed in two molecular forms interpreted as a monomer and a reversible aggregate.
"The two different molecular forms shown to exist probably represent a monomer and an aggregate."
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Thiocyanate can promote disaggregation of salivary LPO preparations.
"The presence of substrate (SCN-) could cause some disaggregation suggesting that the mechanism of the dissociation is influenced by the substrate."
Uric acid and thiocyanate as competing substrates of lactoperoxidase.
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Urate is an alternative bovine-LPO substrate that competes with thiocyanate and suppresses hypothiocyanite production.
"At physiologically relevant concentrations, urate competed effectively with thiocyanate, the main substrate of LPO for oxidation, and inhibited production of hypothiocyanite."
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Human saliva supports peroxidase-dependent urate oxidation, providing physiological context without proving that every reaction is LPO-specific.
"When hydrogen peroxide was added to saliva, oxidation of urate was dependent on its concentration and peroxidase activity."
Crystal structure of lactoperoxidase at 2.4 A resolution.
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Caprine LPO is a single-chain heme peroxidase with two covalent heme ester linkages.
"The structure confirms that the heme group is covalently linked to the protein through two ester linkages involving carboxylic groups of Glu258 and Asp108 and modified methyl groups of pyrrole rings A and C, respectively."
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The LPO distal cavity contains a structured proton-relay path relevant to catalysis.
"Two histidine residues and six buried water molecules are connected through a hydrogen-bonded chain from the distal heme cavity to the surface of protein molecule and seemingly form the basis of proton relay for catalytic action."
Structural evidence for the order of preference of inorganic substrates in mammalian heme peroxidases: crystal structure of the complex of lactoperoxidase with four inorganic substrates, SCN, I, Br and Cl.
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LPO binds thiocyanate, iodide, bromide, and chloride at distinct positions on the distal heme side.
"The structure determination of the complex of LPO with above four substrates showed that all of them occupied distinct positions in the substrate binding site on the distal heme side."
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The crystallographic substrate positions imply a binding preference of bromide over chloride, thiocyanate, and iodide under the structural conditions used.
"Therefore, according to the locations of four substrate anions, the order of preference for binding to lactoperoxidase is observed as Br(-) > Cl(-) > SCN(-) > I(-)."
Excess iodine exposure acutely increases salivary iodide and antimicrobial hypoiodous acid concentrations in humans.
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Acute iodide loading in humans increases salivary iodide and hypoiodous acid, supporting hypohalous chemistry by the salivary LPO system.
"The large iodine load delivered by the angiographic dye, several 100-fold in excess of the U.S. Recommended Daily Allowance for iodine (150 µg/day), significantly increased salivary iodide and HOI levels compared with baseline levels, whereas there was no significant change in salivary SCN- and OSCN- levels."
Lactoperoxidase (LPO) produces OSCN-
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Reactome models human LPO Compound I oxidation of thiocyanate to hypothiocyanite.
"The Reactome event describes the halogenation cycle where LPO-derived Compound I catalyzes the oxidation of thiocyanate ion (SCN-) to hypothiocyanite ion (OSCN-)."