Fig. 5. Ca²⁺/Mg²⁺-ATPase activity of the purified atrial and ventricular myofibrils of the burbot heart. The experiments were conducted at four different temperatures (1, 5, 10 and 15 °C). Dissimilar letters indicate statistically significant differences between different temperatures. Values are means ± S.E.M. of 5-7 preparations.