THERMAL UNFOLDING OF ACANTHAMOEBA MYOSIN-11 AND SKELETAL-MUSCLE MYOSIN

Studies on the thermal unfolding of monomeric Acanthamoeba myosin II a nd other myosins, in particular skeletal muscle myosin, using differen tial scanning calorimetry (DSC) are reviewed. The unfolding transition s for intact myosin or its head fragment are irreversible, whereas tho se of the rod part and its fragments are completely reversible, Acanth amoeba myosin II unfolds with a high degree of cooperativity from ca, 40-45 degrees C at pH 7.5 in 0.6 M KCl, producing a single, sharp endo therm in DSC. In contrast, thermal transitions of rabbit skeletal musc le myosin occur over a broader temperature range (ca, 40-60 degrees C) under the same conditions, The DSC studies on the unfolding of the my osin rod and its fragments allow identification of cooperative domains , each of which unfolds according to a two-state mechanism, Also, DSC data show the effect of the nucleotide-induced conformational changes in the myosin head on the protein stability.