It was demonstrated that denaturation is a one-stage kinetic process. The enthalpy of the of the conformation of -endotoxin in an activated state and its native process and its activation energy were measured as temperature functions. The data obtained allow us to confirm that there is a slight difference in compactness conformation (hydration extent). The comparison of the thermodynamic data for intact -endotoxin and the 55kDa fragment revealed that the molecule transition to an activated state does not result in any changes in the conformation of three N-terminal -helices. Complete removal of the N terminal domain of -endotoxin and 40 amino acids in -structural domain III brings about an irreversible loss of molecular compactness of the thertiry structure. Thus, during protein self-assembly the nucleation core determining protein stability is probably located in the C-terminal part of the molecule and does not envolve its three initial -helices of the N-terminal domain.
Functional significance of peculiarities of structure arrangement of a -endotoxin molecule are discussed.