Combined protective effect of inorganic pyrophosphate and sugar on freeze-denaturation of carp myofibrillar protein.

The effect of addition of inorganic pyrophosphate and sorbitol on freeze denaturation of myofibrillar protein was studied. Carp myofibrils suspension was mixed with sodium pyrophosphate(PPi-Na)or neutralized pyrophosphate (PPi) and subjected to storage at -20°C. The effect of increases in pH or in ionic strength induced by the additives was seaparately ex-amined by measuring the first order rate constant (KD) for freeze-inactivation of myofibrillar Ca-ATPase. The effect of further addition of sorbitol to the myofibrils suspension containing PPi-Na was also examined in the same manner. The results obtained were as follows: (1) The KD increased generally with increasing the ionic strength of the medium for freezing, although theincrease in KD brought about by PPi was somewhat larger than that by KCl. (2) The KD values reached to identical minimum at around pH 7.5, for media adjusted by either PPi-Na or Trismaleate buffer. (3) When the pH of myofibrils suspension was set at 7.5-8.0 by PPi-Na, the protecting effect of sorbitol against the freeze denaturation of myofibrillar protein was greatly enhanced.