Freeze denaturation of carp myofibrils compared with thermal denaturation

The Freeze denaturation mechanism of myofibrils was investigated by comparing with the thermal denaturation. Mg2+-ATPase activity enhancement was brought about in these two denaturation systems, whereas Ca-sensitivity loss was accompanied only in the thermal denaturation. Frozen storage slightly decreased the salt-solubility as well as myosin extractability. The latter change was rather similar to the Ca2+-ATPase inactivation profile. This was in contrast to the case of thermal denaturation, in which myosin extractability as well as solubility dropped very quickly preceding the Ca2+-ATPase inactivation. It was, therefore, concluded that the structural change of myosin caused by freezing is different from that by heating. Myosin rod, a region responsible for the salt solubility of myosin, was suggested to remain undamaged during the frozen storage. It was also found that, when once frozen, myofibrils readily lost their salt solubility upon subsequent heating. It was thus demonstrated that the thermal denaturation process was greatly affected by freezing before heating.