Adsorption Thermodynamics of Toxin (65 kDa) and Protoxin (130 kDa) from Bacillus thuringiensis by Several Minerals

Abstract

The adsorption thermodynamics of toxin (65 kDa) and protoxin (130 kDa) from Bacillus thuringiensis (Bt) by several minerals (montmorillonite, kaolinite and silica) were investigated. The adsorption of toxin and protoxin by minerals was a spontaneous process in the range of temperature from 278K to 318K. The ?G0ads values of the toxin adsorption by above minerals ranged from -35.30 to -43.81 kJ mol-1, and the protoxin adsorption ranged from -35.87 to -44.83 kJ mol-1. The adsorption isotherms of both proteins followed Langmuir equation and the maximum adsorbed amount (Nadsmax) of protoxin were lower than those of toxin. The adsorption of Bt proteins on minerals was exothermic process, companying a negative value of ?H0ads. The ?H0ads values of the adsorption of toxin were between -3.85 and -4.98 kJ mol-1 and the protoxin were between -2.60 and -4.53 kJ mol-1. The standard adsorption entropy changes (?S0ads) of toxin ranged from 110.73 to 122.16 J mol-1 K-1, and of protoxin ranged from 122.57 to 132.77 J mol-1 K-1. The positive standard entropy (?S0ads) indicated that the freedom increased when the insecticidal proteins from B. thuringiensis adsorbed minerals. The Kads, ?G0ads and ?S0ads of toxin in value were lower than those of protoxin, suggesting that the spontaneous trend and the affinity between protoxin and minerals were larger than those of toxin.