Temperature effects on cation affinities of the (Na+, K+)-ATPase of mammalian brain

Effects of temperature on the Na⁺-dependent ADP-ATP exchange and the $\text{p-}\text{nitrophenylphosphatase}$ reactions catalysed by (Na⁺, K⁺)-ATPase were examined. Apparent Mg²⁺ affinity decreased with decreasing temperature. Arrhenius plots of $\text{p-}\text{nitrophenylphosphatase}$ in the presence of Na⁺ and ATP had discontinuities similar to those previously reported for ($\text{Na}{}^{\mathrm{+}}\text{+}\text{K}{}^{\mathrm{+}}\text{)-}\text{ATPase}$, while those of $\text{p-}\text{nitrophenylphosphatase}$ measured without Na⁺ or ATP did not. The apparent activation energy for $\text{p-}\text{nitrophenylphosphatase}$ was a function of the physical characteristics of the cation acting at the K⁺ site.