POST-MORTEM CHANGE OF FISH MYOSINS-II

The previous work indicated that intrinsic viscosity of yellowtail or mackerel decreases so far as to 0.5-0.2 after the muscle has passed into rigor. As intrinsic viscosity is too low, however, a question has been left open whether or not the myosins fraction from yellowtail or mackerel at the in-rigor or post-rigor stage is consists of really actomyosin. Measurement of ATP sesitivity. In order to identify actomyosin, ATP sensitivity has been employed according to PORTZEHL et al. The ATP sensitivity is defined as (Zη-ZηATP/ZηATP)×100 where Zη and ZηATP are the viscosity number before and after addition of ATP, respectively. In the case of rabbit muscle the viscosity number has been reported to be independent of its concentration. However, as shown in the author's previous paper3), the viscosity number of fish actomyosin is greatly influenced by its concentration. Then, it is proposed that both Zη and ZηATP may be expressed by extrapolating these values into zero of the protein concentration. Namely, ATP sensitivity=(Zηc->o-ZηATPc->o/ZηATPc->o)×100 This sample fish were killed by beheading; a portion of muscle was taken and subjected to experiments immediately after death, while other portions of the muscle were taken after storing them for 24 and 70-90 hrs. at ca. 3°C. In yellowtail, ATP sensitivity of myosins fraction was found to increase in the following order with respect to the post mortem phase: pre-rigor