Abstract
1. The endogenous phosphorylation of mouse brain microsomes was studied using the technique of acrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS).
2. It was found that specific proteins and lipids in brain microsomes were phosphorylated by the terminal phosphate of ATP under appropriate conditions. Six peaks of radioactivity were observed on SDS-polyacrylamide gel electrophoresis of 32P1-labelled brain microsomes. The peaks were designated as P-I, P-II, P-III, P-IV, P-V, and P-VT. The peaks from P-I to P-V, which consist of phosphoproteins, underwent rapid dephosphorylation. On the other hand, P-VI, which consists of phospholipids, remained unaffected even after the complete hydrolysis of added ATP.
3. With the addition of 100μM CaCl2 to the assay medium, the phosphorylation of brain microsomal proteins was stimulated; in the regions of P-I, P-II, and P-III, the amounts of 32P1 incorporation were approximately twice the 32P1 incorporation in the absence of Ca2+. On the other hand, 32P1 incorporation into P-VI was unaffected irrespective of the presence or absence of 100μM CaCl2. In the presence of higher concentrations of Ca2+ (1-10mM), the phosphorylation of all components was inhibited.
