THERMALLY-INDUCED CHAIN EXCHANGE OF SMOOTH-MUSCLE TROPOMYOSIN DIMERS STUDIED BY DIFFERENTIAL SCANNING CALORIMETRY

The thermal unfolding of duck gizzard tropomyosin dimers, alpha beta, alpha alpha, and beta beta, and of a 1:1 mixture of alpha alpha and be ta beta homodimers was studied by differential scanning calorimetry (D SC). Both alpha alpha and beta beta homodimers demonstrated a broad th ermal transition with maxima at 37.4 degrees C and 44.6 degrees C, res pectively. However, a sharp cooperative thermal transition at 41.5 deg rees C characteristic for alpha beta heterodimer appeared on the therm ogram of the mixture of homodimers, The appearance of this transition was prevented by disulfide cross-linking of polypeptide chains in the homodimers, Thus, DSC studies clearly demonstrate formation of tropomy osin heterodimers during heating of the mixture of homodimers and in a greement with earlier published reports indicate thermally induced cha in exchange between tropomyosin dimers, (C) 1998 Federation of Europea n Biochemical Societies.