title: The ecto-5'-nucleotidase subunits in dimers are not linked by disulfide bridges but by non-covalent bonds.
abstract: It has long been considered that ecto-5'-nucleotidase (eNT) dimers consist of subunits linked by disulfide bonds. Hydrophilic (6.7S) and amphiphilic (4.0S) dimers were separated by sedimentation analysis of eNT purified from bull seminal plasma. Hydrophilic (4. 2S) and amphiphilic (2.6S) eNT monomers were obtained after reduction of disulfide bonds in dimers. The amphiphilic eNT dimers or monomers were converted into their hydrophilic variants with phosphatidylinositol-specific phospholipase C. SDS-PAGE plus Western blot showed 68 kDa subunits, regardless of the addition of beta-mercaptoethanol to the SDS mixture. Active eNT monomers were obtained by addition of 1 M guanidinium chloride (Gdn) to dimers, and unfolded subunits by addition of 4 M Gdn. The results unambiguously demonstrate that the subunits in eNT dimers are not linked by disulfide bridges, but by non-covalent bonds, and that dissociation precedes inactivation and unfolding.
authors.affiliation: Departamento de Bioquímica y Biología Moleclar A, Edificio de Veterinaria, Universidade de Murcia, Espinardo, Spain.
authors.forename: A
authors.initials: A
authors.lastname: Martínez-Martínez
authors.forename: E
authors.initials: E
authors.lastname: Muñoz-Delgado
authors.forename: F J
authors.initials: FJ
authors.lastname: Campoy
authors.forename: C
authors.initials: C
authors.lastname: Flores-Flores
authors.forename: J N
authors.initials: JN
authors.lastname: Rodríguez-López
authors.forename: C
authors.initials: C
authors.lastname: Fini
authors.forename: C J
authors.initials: CJ
authors.lastname: Vidal
mesh_terms: D015720:5'-Nucleotidase / Q000737:chemistry*; D000818:Animals; D002417:Cattle; D002499:Centrifugation, Density Gradient; D002851:Chromatography, High Pressure Liquid; D019281:Dimerization; D004229:Dithiothreitol; D004591:Electrophoresis, Polyacrylamide Gel; D019791:Guanidine; D008297:Male; D020836:Protein Structure, Quaternary; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D014508:Urea
chemical_list: D013438:Sulfhydryl Compounds; D014508:Urea; D015720:5'-Nucleotidase; D019791:Guanidine; D004229:Dithiothreitol