MOLECULAR PROPERTIES OF POST‐MORTEM MUSCLE. 9. Effect of Temperature and pH on Tropomyosin‐Troponin and Purified α‐Actinin from Rabbit Muscle

SUMMARY– A study was done on the effects of in vitro storage of purified α‐actinin, troponin, tropomyosin, and the tropomyosin‐troponin complex on the activity of these protein fractions in the ATPase and superprecipitation assays. Storage was done at various combinations of temperatures between 0 and 40°C and pH values between 5.7 and 7.0. Even after 40 hr of storage, activities of purified tropomyosin and the tropomyosin‐troponin complex were not affected by any combination of temperature and pH included in this study, but activities of purified α‐actinin and troponin were almost completely lost after 16 hr at 40°C and pH 5.7. Storage for 40 hr at low pH (5.7) and low temperatures (0°C) did not affect the activity of either α‐actinin or troponin, but 40 hr of storage at high temperatures (40°C) and neutral pH caused some loss in activity for both these proteins. This loss of activity caused by 40°C, pH 7.0 storage was much more noticeable in the case of troponin than in the case of α‐actinin. Storage periods of 40 hr or longer were required before any loss of α‐actinin activity could be detected at pH 7.0 and 40°C. Since most meat animal carcasses are chilled soon after exsanguination and attain muscle temperatures of 25°C or lower before the pH falls below 6.2, it is probable that α‐actinin and tropomyosin‐troponin activity remain almost unchanged in meat handled through normal market channels. However, myofibrillar tissue in those porcine animals whose musculature undergoes a very rapid post‐mortem decline in pH so that values of 5.7 or less are reached while muscle temperatures are still 37°C or higher may lose much of its α‐actinin and tropomyosin‐troponin activity during the first 24 hr post‐mortem.