Temperature dependence of brain ATPases in immature and adult rats

In immature rats the temperature dependence of Na+-K+ ATPase of a crude homogenate of brain shows a compex curve with two activity maxima. When EDTA was present in the homogenization medium the curve obtained was of simpler, curvilinear type showing an increased activity at temperatures above 20 degrees C. The Na+-K+ ATPase activity in similar preparation from adult brain were not complex but curvilinear whether EDTA was used or not; however, EDTA increased the activity at temperatures above 20 degrees C. When such chelating agents as EDTA or histidine were used in preparation of microsomes from immature rat brain, the temperature dependence curve of Na+-K+ ATPase in this membrane fraction was changed to a steeper and simpler curve with increased activity especially at temperatures above 20 degrees. These agents, however, did not eliminate totally the complex shape of curve found in microsomes prepared without the presence of any chelating agents. When microsomes were prepared by using NaI-technique the temperature dependence of this enzyme was linear between temperatures 15-14 degrees, the activity being 4-5-fold higher than in the ordinary microsomal preparation. A stimulation of the Mg2+ ATPase by Na+ ions (100mM) was found at temperatures below 30 degrees but an inhibition by the same concentration of Na+ at upper temperatures. This effect together with the lowered activity due to bivalent metal ions (e.g. Ca2+, Cu2+) in 'crude' preparations was thought to be reasons for the complex shape of temperature dependence curve of Na+-K+ ATPase activity.