title: Dielectric properties of Bauhinia monandra and concanavalin A lectin monolayers, part I.
abstract: The dielectric properties of the galactose-binding lectins Bauhinia monandra (BmoLL) and Concanavalin A (Con A) were assessed by surface potential measurements of their spread monolayers on an aqueous subphase containing a monovalent electrolyte. For both lectins the curves of surface potential versus mean molecular area (DeltaV-A) and the independently recorded isotherms of surface pressure versus mean molecular area (Pi-A) were shown to be pH-dependent. As the subphase pH changed from 2 to 9, a noticeable trend to higher surface pressures accompanied the compression of the monolayers. Conversely, the surface potentials values of both monolayers decreased with increasing pH. For Con A, with the single exception of the pH 9 case, lowering the pH yielded DeltaV values higher than those for BmoLL. The contribution of the electric double layer (Psi0) to the overall DeltaV values at a given Pi (15 mN/m) was calculated using a modified Davies equation and assuming that at this surface pressure the monolayers of both studied lectins were stable. While at all studied pHs the Psi0 values for Con A exceeded those calculated for BmoLL, for both lectins they were insensitive to pH changes. This provided evidence that the reorientation of lectin molecules, during compression predominantly contributed to the alteration of the overall DeltaV values. The calculated Psi0 values made possible the evaluation of the dipole moments for BmoLL and Con A, and it has been estimated that the decrease in the pH of the subphase from 9 to 2 produced a 1.6-fold (twofold) increase in the value of for BmoLL (Con A). The differences in dielectric properties between the two film-forming lectins have been attributed to the differences in their structures. Indeed, the circular dichroism (CD) spectrum of Con A showed the predominance of beta-plated sheet structures while that of BmoLL was typically rich in alpha-helix structures.
authors: Pós-Graduação em Ciência de Materiais, Universidade Federal de Pernambuco, 50670-901 Recife, PE, Brazil.
authors: Cesar A S
authors: CA
authors: Andrade
authors: Adam
authors: A
authors: Baszkin
authors: Nereide S
authors: NS
authors: Santos-Magalhães
authors: Luana C B B
authors: LC
authors: Coelho
authors: Celso P
authors: CP
authors: de Melo
mesh_terms: D036481:Bauhinia / Q000737:chemistry*; D001665:Binding Sites; D002942:Circular Dichroism; D003208:Concanavalin A / Q000737:chemistry*; D004553:Electric Conductivity; D004573:Electrolytes; D005690:Galactose / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D037102:Lectins / Q000737:chemistry* / Q000302:isolation & purification; D018515:Plant Leaves / Q000737:chemistry; D012680:Sensitivity and Specificity; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D004573:Electrolytes; D037102:Lectins; D014867:Water; D003208:Concanavalin A; D005690:Galactose