title: Spectroscopic and binding studies on the interaction of inorganic anions with lactoperoxidase.
abstract: The interaction of several inorganic species (SCN-, I-, Br-, Cl-, F-, NO2-, N3-, CN-) with bovine lactoperoxidase was investigated through kinetic and binding studies by using UV-Vis spectroscopy. The above ligands form 1:1 complexes with the protein and can be assigned to three different groups, on the basis of the dissociation constant values (KD) of the adducts: (1) SCN-, I-, Br-, and Cl- (KD increases along the series); (2) F- (which shows a singular behavior); (3) NO2-, N3-, and CN- (that bind at the iron site). KD values for the LPO/SCN- adduct appeared to be modified in the presence of other inorganic species; a strong competition between this substrate and all other anions (with the exception of F-) was evidentiated. Binding investigations on the natural substrates SCN- and I-, at varying pH and temperature, showed that their interaction with lactoperoxidase involves the protonation of a common site in proximity of the iron (possibly distal histidine). Michaelis-Menten constants for SCN-, I-, and Br- followed roughly the same trend as KD; KM for hydrogen peroxide is strongly dependent on the cosubstrate. Computer-assisted docking simulations showed that all ligands can penetrate inside the heme pocket.
authors.affiliation: Dipartimento di Chimica I.F.M., Università di Torino, Italy. ferrari@ch.unito.it
authors.forename: R P
authors.initials: RP
authors.lastname: Ferrari
authors.forename: E M
authors.initials: EM
authors.lastname: Ghibaudi
authors.forename: S
authors.initials: S
authors.lastname: Traversa
authors.forename: E
authors.initials: E
authors.lastname: Laurenti
authors.forename: L
authors.initials: L
authors.lastname: De Gioia
authors.forename: M
authors.initials: M
authors.lastname: Salmona
mesh_terms: D000818:Animals; D000838:Anions / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D001667:Binding, Competitive; D001965:Bromides / Q000737:chemistry / Q000378:metabolism; D002417:Cattle; D003198:Computer Simulation; D006863:Hydrogen-Ion Concentration; D007454:Iodides / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D007784:Lactoperoxidase / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D013057:Spectrum Analysis / Q000379:methods*; D013696:Temperature; D013861:Thiocyanates / Q000737:chemistry / Q000378:metabolism
chemical_list: D000838:Anions; D001965:Bromides; D007454:Iodides; D013861:Thiocyanates; D007784:Lactoperoxidase; C031760:thiocyanate