A protein kinase assayable with intact cells of the cellular slime mold Dictyostelium discoideum

A protein kinase activity assayable with whole cells of the slime mold is described. This activity is largely lost if the cells are disrupted by sonication or freeze-thawing. The cation and pH requirements of the enzyme are described. Neither cAMP nor dibutyryl cAMP stimulate the activity under a variety of conditions. In addition, cells harvested from different periods in the growth cycle or from different stages in development yielded the same activity per cell and showed no cAMP or dibutyryl cAMP effect. With histone type II as the substrate, the product of the reaction was judged to be a phosphorylated serine or threonine by its lability in hot alkali and its stability to hot acid.