title: NMR studies of primary and secondary sites of parvalbumins using the two paramagnetic probes Gd (III) and Mn (II).
abstract: The binding of cations by parvalbumins was studied by the proton relaxation enhancement (PRE) method using the paramagnetic probes Gd(III) and Mn(II). Gd(III) appears as a specific probe of the primary sites CD and EF with the following binding parameters: n = 2, KdGd = 0.5 x 10(-11) M and epsilon b = 2.3. The low value of epsilon b is the result of a nearly complete dehydration of the protein bound ions. Competition experiments between Gd(III) and various diamagnetic cations show the following order of affinity for the EF and CD sites: Mg2+ less than Zn2+ less than Sr2+ less than Ca2+ less than Cd2+ less than La3+ less than or equal to Gd3+. Mn 2+ is a specific probe of a secondary site with the following binding parameters: n = 1, KdMn = 0.6 x 10(-3) M and epsilon b = 17. The high value of epsilon b suggests that the protein bound Mn(II) has retained most of its hydration shell. Competition experiments between (Mn(II) and different cations show similar affinities for this site: Ca2+ less than or equal to Mg2+ less than or equal to Cd2+ less than or equal to Mn2+. This secondary site is located near the EF primary site.
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002347:Carps; D002413:Cations, Divalent; D005682:Gadolinium; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008345:Manganese; D009124:Muscle Proteins; D010320:Parvalbumins; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D009124:Muscle Proteins; D010320:Parvalbumins; D008345:Manganese; D005682:Gadolinium