PURIFICATION AND CHARACTERIZATION OF AN AUTOPHOSPHORYLATION-ACTIVATEDPROTEIN SERINE THREONINE KINASE THAT PHOSPHORYLATES AND INACTIVATES PROTEIN PHOSPHATASE-2A

Protein phosphatase 2A2 is inactivated by phosphorylation following in cubation with purified preparations of an autophosphorylation-activate d protein kinase (Hong Guo and Zahi Damuni (1992) Proc. Natl. Acad. Sc i. U. S. A. 90, 2500-2504). This protein kinase was purified about 250 ,000-fold from extracts of bovine kidney to apparent homogeneity. The purified preparations exhibited a single polypeptide of apparent M(r) almost-equal-to 36,000. Up to 1 mol of phosphoryl groups was incorpora ted per mol of the purified kinase following incubation with ATP. This autophosphorylation reaction (t1/2 almost-equal-to 0.5-1 min) was acc ompanied by a approximately 10-fold activation of the kinase. Autophos phorylation and activation were reversed by protein phosphatase 2A2 or the catalytic subunit of protein phosphatase 1. Phosphoamino acid ana lysis indicated that the kinase underwent autophosphorylation on threo nines. The rate of autophosphorylation was independent of the concentr ation of the enzyme and a slope of 0.97 (gamma = 0.998) was obtained b y van't Hoff's plot indicating that autophosphorylation was intramolec ular. Relative to myelin basic protein, the enzyme exhibited about 8, 62, 130, 33, 5, and <0.1% activity with histones H1, H2A, H2B, H3, and H4 and with glycogen synthase a, respectively. Heparin inhibited the activity of the enzyme half-maximally at about 20 mug/ml. The results indicate that this autophosphorylation-activated kinase is a new prote in kinase.