Assay of total protein kinase activity in mouse brain cortex.

In previous studies we demonstrated that the adrenergic system is impaired in old animals and that the main alterations were observed at the level of receptor density and adenylate-cyclase activity. The decreased ability to produce cAMP could influence the activity of the cAMP dependent protein kinase (PKA), one of the enzymes responsible for the phosphorylation of protein substrates. Since protein phosphorylation is one of the most common and important mechanisms through which a cell regulates its activity, the characteristics of the phosphorus incorporation reaction were studied. Kinase activity was measured in homogenate of young mouse brain cortex prepared avoiding gross manipulations in order to maintain conditions as close to those present in the living animal as possible. Results show that phosphate incorporation is proportional to protein content and strictly dependent on ATP availability. Increasing the ATP concentration from 10 to 500 mumol/l, the length of incorporation phase increases, suggesting that the limiting point of the reaction is better represented by energy availability than by enzyme or protein substrate concentrations.