Multiple forms of phosphoprotein phosphatase and its protein inhibitors from rat brain

By means of Sephadex A-50 ion exchange chromatography 5 peaks of phosphoprotein phosphatase (PPase) activity have been detected in rat brain. These molecular forms of the enzyme differ from each other by their specific activity as well as by a number of other properties--pH optima, heat and storage stability, and substrate specificity. It was shown that cyclic AMP (10(-5)-10(-6) M) decreased PPase activity of the majority of the peaks (I-III, V) and increased that of the peak IV. Ion exchange chromatography of brain tissue extracts revealed 4 peaks of PPase protein inhibitors. The results obtained on dialysis and tryptic digestion point to the protein nature of the inhibitors that differed from each other by their effect on the enzyme activity and heat stability (95 degrees C, 5 min). The significance of the specificity of separate molecular forms of PPases is discussed.