Endogenous phosphorylation of soluble enzymes in human red cells Cyclic 3′,5′-AMP-dependent phosphorylation of phosphofructokinae without detectable regulatory effect

Abstract

ATP-depleted human red cells have been incubated in a glucose-containing medium with [ 32P]orthophosphate in the presence and in the absence of cyclic 3′,5′-AMP and dibutyril cyclic 3′,5′-AMP. Spectrin, pyruvate kinase, phosphofructokinase, glucose-6-phosphate dehydrogenase and hemoglobin A 1 have been purified and analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Protein-bound radioactivity has been measured from the sodium dodecyl sulfate polyacrylamide gels and the trichloroacetic acid-precipitated proteins. In the cytosol, the most intense phosphorylation was found for pyruvate kinase whose, in the presence of cyclic AMP, specific radioactivity was comparable to that of the membrane protein and spectrin. In the absence of cyclic nucleotides it was five times less phosphorylated. Phosphofructokinase was only phosphorylated when the red cells were incubated with cyclic nucleotides; the extent of phosphorylation was four times less than for pyruvate kinase. Hemoglobin, glucose-6-phosphate dehydrogenase and a contaminant protein copurified with phosphofructokinase were not phosphorylated: the ‘back-ground’ of the radiaoctivity found for these proteins was 100 times less than for pyruvate kinase and spectrin, and 20 times less than for phosphofrutoskinase (+cyclic AMP).