Abstract
At a temperature range from -5°C to 20°C, the Arrhenius plot of the dephosphorylation of nucleotides in cod muscle exhibited one break point at around -2°C, the plot of carp muscle at about 5°C, but the plot of yellowtail exhibited two break points at around -2°C and 10°C. These break points at around -2°C disappeared on the addition of glycerin as an antifreeze. The Arrhenius plots of microsomal 5'-nucleotidase of carp and yellowtail exhibited one break point at 5°C and 10°C respectively, but the plot of cod showed no break point, in the presence of glycerin. The Km of microsomal 5'-nucleotidase of carp and yellowtail for IMP markedly increased with descending temperature below the break point. The break point of microsomal 5'-nucleotidase disappeared on the treatment with a surfactant. Therefore, the assumption made is, that the change in kinetics of dephosphorylation of nucleotides at around -2°C may be accounted for by the phase change of water in fish muscle, and the change at the temperature above freezing point may be accounted for by the lipid phase separation in membranes containing 5'-nucleotidase at the definite temperature which is specific to the species of fish.
