Different Freeze Denaturation of Myosin and Actin in Myofibrils and in Muscle

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  • 筋肉と筋原線維で異なるミオシンとアクチン凍結変性
  • キンニク ト キン ゲン センイ デ コトナル ミオシン ト アクチン トウケツ ヘンセイ

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Freeze denaturation of myosin and actin when stored in a form of meat and in myofibrils (Mf) (0.1 M NaCl, pH 7.5) was compared at -20<tt>˚</tt>C. Frozen storage of Mf inactivated its Ca2+-ATPase activity almost completely in 8 days. Decrease of monomeric myosin content occurred similarly to Ca2+-ATPase inactivation, while myosin kept its solubility in 0.5 M NaCl during the frozen storage period. Chymotryptic digestion of the frozen stored Mf showed a slight damage at rod portion. The chymotryptic digestion of the Mf also demonstrated a severe actin denaturation as detected by a drastic decrease of actin content in the digest. Denaturation profile of actin was similar to Ca2+-ATPase inactivation. On the other hand, such myosin and actin denaturation was not observed when flounder muscle was frozen stored at -20<tt>˚</tt>C. To study myosin and actin denaturation in frozen stored meat, muscle was converted into muscle homogenate quantitatively. Frozen storage of meat up to 60 days denatured myosin very slightly exhibiting roughly 75 % of Ca2+-ATPase activity. Practically no detectable actin denaturation was found with the same frozen stored meat. It was thus demonstrated that actin denaturation in Mf caused quick myosin denaturation in it. Thus, Mf is not a suitable model for studying freeze denaturation of myosin and actin in fish meat.

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