Abstract
It is known that myosin B (MB)-Ca^<2+>-ATPase activity decreases by the salt concentration during freezing, which occurs at temperature above the eutectic point of salt solution. The salt concentration is caused by the phase transition of water. But, quantitative relationship between the phase transition of water and the decrease in MB-Ca^<2+>-ATPase activity had been investigated and clarified. To predict and control the denaturation of protein which participate in the management of fish preservation, the relationship between the cryohydration and effect of salt concentration on MB-Ca^<2+>-ATPase activity during freezing in the KCl-NaCl complex solution was examined thermodynamically. The salt concentration of KCl-NaCl with 300mM-300mM in the beginning increased to 564mM-2936mM near the eutectic point. Tilapia MB Ca^<2+>-ATPase activity decreased during reaction in high salt concentrations of prepared KCl-NaCl complex solutions at 25℃. The difference between the experimental heat quantity of solidification in the solution and the calculated one was in the range of 3%. It was considered that there was no effect of dilute MB (protein concentration, 0.37mg/ml) on the heat quantity, and MB-KCl-NaCl complex solution system was treated as the KCl-NaCl complex solution system, because the MB-KCl-NaCl complex solution had the same freezing temperature as the KCl-NaCl complex solution without MB. It was found that the changes of Gibbs free energy (ΔG) for the Ca^<2+>-ATPase reaction system was correlated to ones calculated from the heat of solidification for the KCl-NaCl complex solution.
