title: Evidence for a tetrameric form of iceberg lettuce (Lactuca sativa L.) polyphenol oxidase: purification and characterization.
abstract: Polyphenol oxidase from iceberg lettuce (Lactuca sativa L.) chloroplasts was released from the thylakoid-membrane by sonication, and it was extensively purified to homogeneity as judged by SDS-PAGE. Purification was achieved by ammonium sulfate fractionation, gel-filtration chromatography, and ion-exchange chromatography. Two molecular forms were separated by gel-filtration chromatography with apparent molecular masses of 188 and 49 kDa. Both forms were characterized by sedimentation analysis with S(20,W) values of 10.2 and 4.1 S, respectively. For the high-molecular-weight form purified to homogeneity, denaturing SDS-PAGE indicated a molecular mass of 60 kDa. Thus, from these data we suggest that lettuce polyphenol oxidase is a tetramer of identical subunits.
authors.affiliation: Departamento de Bioquímica y Biología Molecular A, Edificio de Veterinaria, Unidad docente de Biología, Universidad de Murcia, Campus de Espinardo, 30071, Murcia, Spain.
authors.forename: S
authors.initials: S
authors.lastname: Chazarra
authors.forename: F
authors.initials: F
authors.lastname: García-Carmona
authors.forename: J
authors.initials: J
authors.lastname: Cabanes
mesh_terms: D000645:Ammonium Sulfate; D000838:Anions; D004156:Catechol Oxidase / Q000737:chemistry* / Q000302:isolation & purification*; D002736:Chloroplasts / Q000201:enzymology; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004591:Electrophoresis, Polyacrylamide Gel; D005590:Fractional Precipitation; D018545:Lactuca / Q000201:enzymology* / Q000648:ultrastructure; D046911:Macromolecular Substances; D008970:Molecular Weight; D011189:Potassium Chloride; D021122:Protein Subunits; D013010:Sonication
chemical_list: D000838:Anions; D046911:Macromolecular Substances; D021122:Protein Subunits; D011189:Potassium Chloride; D004156:Catechol Oxidase; D000645:Ammonium Sulfate