Isolation of phosphorylated acid chloroform/methanol-soluble proteins from live frog muscle

About 6-7% of the total proteins from trichloroacetic acid-washed and freeze-dried frog muscle could be extracted with acid chloroform/methanol. Three of these proteins were found to be phosphorylated in the live frog. They were purified to apparent homogeneity by gel chromatography and preparative gel electrophoresis. The apparent molecular weights, determined by sodium dodecyl sulfate gel electrophoresis, were 34 000, 19 000 and 10 000. Each phosphorylated protein contained 3 mol of a covalently bound neutral sugar but they did not contain any tightly bound lipids. All three proteins incorporated 32P into serine phosphate. The 10 000 dalton protein, which had the highest specific radioactivity contained an unusually high proportion of serine, 14% of the total amino acids. It also did not stain with Coomassie Blue.