Changes in the $Ca^{2+}-,\;Mg^{2+}-dependent$ Adenosine Triphosphatase Activity and Ultrastructure of Marine Fishes by Partial Freezing -I. Denaturation of Yellowtail Myofibrillar ATPase During Cold Storage-

해산어의 부분동결에 의한 $Ca^{2+}-,\;Mg^{2+}-dependent$ Adenosine Triphosphatase 활성 및 근섬유의 미세구조의 변화 -I. 저온저장에 의한 방어 근원섬유 단백질의 변성-

Myofibrillar protein(myofibil) was prepared from Yellowtail fish (Seriola quinqueradiata), and then, it was stored at $0^{\circ}C$(ice-cooling), $-3.5^{\circ}C$(partial freezing) and $-20^{\circ}C$(freezing). Another myofibrils were prepared from the fish stored with ice-cooling, partial freezing and freezing for a week as the maximum. Denaturation of muscle protein during the storage was investigated by the measurement of $Ca^{2+}-$ and $Mg^{2+}-ATPase$ activity. Specific activity of $Ca^{2+}-\;and\;Mg^{2+}-ATPase$ associated with Yellowtail myofibrils was 0.155 and $0.149\;{\mu}\;mole$ Pi/min/mg of protein, respectively, before storgae. ATPase activity of myofibils did not show any significant difference between $0^{\circ}C$ and $-3.5^{\circ}C$ whereas it was decreased faster at $-20^{\circ}C$ than at $0^{\circ}C$ or $-3.5^{\circ}C$. ATPase activity of myofibirls extracted from the fish stored for a week was 1.2-1.8 times higher than myofibils stored with ice-cooling or partial freezing while it was 2.5-3 times higher than that with freezing. Apparent denaturation constant of $Ca^{2+}-ATPase$ of myofibrils was between 0.48-0.65, and it was 2-3 times higher than that of $Mg^{2+}-ATPase$. The constant of myofibrils extracted from the fish did not show significant difference between $Ca^{2+}-\;and\;Mg^{2+}-ATPase$.

방어로부터 추출한 근원섬유 현탁액을 $0^{\circ}C$(빙장), $-3.5^{\circ}C$(PF저장), $-20^{\circ}C$(동결저장)에 저장하면서 Ca-과 Mg-ATPase활성을 측정하여 근육단백질의 변성을 조사하였으며 일부는 생선을 각 온도에 일정기간 저장한 후 근원섬유를 추출하여 단백질 변성정도를 비교한 결과 추출한 근원섬유를 저장하였을 때 빙장 및 PF저장한 시료의 ATPase활성은 비슷한 수준이었으나 동결 저장한 시료에서는 현저히 낮았다. 생선을 각 온도에 1주일간 저장한 후 추출한 근원섬유의 소활성은 근원섬유를 미리 추출하여 같은 기간동안 저장한 경우에 비하여 빙장과 PF저장에서는 1.2-1.8배, 동결저장에서는 2.5-3배 정도 높은 수준을 유지하고 있었다. 근원섬유를 각 온도에 저장하였을 때의 변성속도는 Ca-의 경우가 Mg-ATPase에 비 해 2-3배 빨랐으나 생선으로 저장한 경우에는 Ca-과 Mg-ATPase간에 큰 차이를 나타내지 않았다.