Involvement of type 2C phosphatase in the dephosphorylation of 26 kDa phosphoprotein in rat parotid acinar cells.

Phosphorylation of three particulate proteins with molecular masses of 34, 26, and 22 kDa was stimulated in the presence of cyclic AMP/3-isobutyl-1-methylxanthine in saponin-permeabilized rat parotid acinar cells. When the particulate fraction isolated from the cells labeled with [gamma-32p]ATP was incubated at 30 degrees C, dephosphorylation of the 26 kDa phosphoprotein occurred in the presence of Mg2+ or Mn2+. Okadaic acid had no effect on the Mg(2+)-dependent dephosphorylation of the 26 kDa phosphoprotein. Addition of the recombinant type 2C phosphatase, Mg(2+)-dependent and okadaic acid-insensitive phosphatase, caused a remarkable dephosphorylation of the 26 kDa phosphoprotein. These observations strongly suggest type 2C phosphatase is involved in the dephosphorylation of the 26 kDa phosphoprotein.