constant expression and activity of protein phosphatase 2a in synchronized cells the levels of the a b and c subunits of protein phosphatase 2a in extracts from synchronized embryonic bovine tracheal cells were determined by immunoblotting with subunitspecific antibodies a constant amount of each subunit was found in resting cells as well as in growing cells from all stages of the cell cycle the phosphatase activity of protein phosphatase 2a was also constant a quantitative comparison showed that the a and c subunits were present in similar amounts whereas the b subunit was present at a significantly lower level together the a b and c subunits represented approximately 02 of the total cellular protein