Viscometric data obtained after tryptic digestion of actomyosin and myosin from several fish species, when plotted as the logarithm of Z_η' (viscosity number) reveals that the hydrolysis proceeds through two distinct first order reactions in all of the fish species.
The initial values for viscosity numbers of different preparations may show minor variations, but a perfect fit is obtained by plotting subsequent changes as the logarithm of relative values assuming the initial value as one.
A comparison of the rate constants of decline in viscosity (K') shows that rabbit and tilapia actomyosins and myosins are almost equally susceptible to trypsin. Approximate rate constants were also obtained for carp, skipjack and yellowfin tuna actomyosins, whereas bigeye tuna proteins showed higher susceptibility. Shark actomyosin was shown to be two times more susceptible than that of carp. Yellowtail, flatfish and cod myofibrillar proteins comprise the most unstable group.
There is a systematic relationship between the extent of stability shown by the actomyosin of a particular species and its myosin.
Since denatured and fresh actomyosins were digested at the same rate, the higher susceptibility of the most unstable species appears to be a function of tryptic digestion only.