Phosphoprotein as an Intermediate in Cerebral Microsomal Adenosine-triphosphatase

Abstract

MICROSOMAL and cell membrane fractions from cerebral cortex contain a powerful ATP-splitting system, activated by Mg²⁺, Na⁺ and K⁺ and inhibited by the cardiac glycoside ouabain^1–6. The nature of the ATP-splitting reaction is not clear; but recently it has been reported that a phosphorylated intermediate is involved in the splitting of ATP by guinea pig kidney cortex¹³, human erythrocyte membranes¹⁴ and the electric organ of the electric eel¹⁵. This note provides evidence that phosphoprotein from cerebral cortex becomes labelled during the splitting of AT³²P by the ATPase, and that the time-course of uptake of labelled phosphate from ATP into the phosphoprotein fraction and into inorganic orthophosphate is indicative of the phosphoprotein being a precursor of inorganic phosphate.