IRREVERSIBLE BINDING-KINETICS OF BACILLUS-THURINGIENSIS CRYIA DELTA-ENDOTOXINS TO GYPSY-MOTH BRUSH-BORDER MEMBRANE-VESICLES IS DIRECTLY CORRELATED TO TOXICITY

To examine the binding of Bacillus thuringiensis delta-endotoxins, CryIAa, CryIAb, and CryIAc, to Lymantria dispar (gypsy moth) brush border membrane vesicles (BBMV), saturation kinetic analyses were conducted according to a two-step interaction scheme [GRAPHICS] for delta-endotoxin binding to BBMV, rather than the one-step reversible binding presented in prior reports. The order of toxicity of the delta-endotoxins, as measured by the dose required for a 50% inhibition of weight gain (ID50), was CryIAa (77.3 ng) > CryIAb (157 ng) > CryIAc (187 ng). While both the maximum extent of binding, B-max and the half-maximum insertion rate concentration, K-1/2 was observed to be indirectly related to toxicity, the rate constant of irreversible binding, k(2), was found to be directly correlated to toxicity.