Process of Denaturation of Arachin by Heat Treatment

Abstract

When arachin 0_20)W, 9S) was heated in 0.01 m sodium phosphate buffer, pH 7.9, at 70°C, the 9S protein decreased, accompanied by an increase of the 3S component and precipitate. The 3S component was not precipitated by prolonged heating. The precipitate contained six arachin subunits (S₁ to S₆) in a molar ratio of 3/4: 3/4: 3/4.1:1:1, but the 3S component comprised S_l5 S₂ and S₃ as dissociated forms in an equimolar ratio. The molar ratio of S_x, S₂ and S₃ in the 3S component to those in the precipitate was 1: 3 at each time of heating. On the other hand, arachin was neither dissociated nor precipitated by heating in 0.3 m sodium phosphate buffer, pH 7.9. The fluorescence intensity of l-anilino-8-naphtalene sulfonate (ANS) conjugated with the heated arachin in 0.3 m buffer, however, was stronger than that of ANS conjugated with the intact arachin. These results suggest that two different pathways leading to insolubilization are involved in the thermal denaturation of arachin.