The effects of pH and temperature on the stability of myofibrils from some fish species have been studied in terms of the first order rate constant (K_D) for inactivation of Ca-ATPase.
The myofibrils were incubated at various pH values while maintaining the temperature constant, though the temperature applied for incubation was different for each fish species.
1. Myofibrillar Ca-ATPase was found to be more resistant to thermal inactivation in the neutral range of pH 7.0-8.5.
2. The inactivation rates of myofibrillar Ca-ATPases at acidic pH below 6.9 and at al-kaline pH above 8.6 were faster than that observed at neutral pH, 2-7 times faster depending upon pH values.
The rate constants (K_D) were plotted semilogarithmically against the reciprocal of absolute temperature for incubation.
3. Linear A_RRHENIUS plots in the temperature range of 20-35°C were identifiable for sardine myofibrils at pH 5.8 and atka-mackerel myofibrils at 7.6.
4. The rate of inactivation of the Ca-ATPase of sardine rnyofibrils at pH 5.8 and 5°C was found to be comparable with that of Ca-ATPase at 7.6 and 26°C.
The significance of these results is discussed in relation to the rapid deterioration of sardine muscle during storage under various environmental conditions.