[37] Protein phosphatase-1 and protein phosphatase-2A from rabbit skeletal muscle

This chapter describes the purification of two forms of protein phosphatase- 1 (PP-I1 and PP-lG), and three forms of protein phosphatase-2A (PP-2A0, PP-2A1, and PP-2A2) from skeletal muscle. Procedures for isolating the free catalytic subunits (termed PP-lc and PP-2Ac) are documented and the structures of these enzymes are summarized in the chapter. The free catalytic subunits are isolated by a modification of the procedure of Lee and co-workers. Skeletal muscle extracts prepared from 3000 g of muscle are adjusted to pH 7.2 with 10 M ammonium hydroxide, and 350 g of solid ammonium sulfate are added to each liter of solution to bring the degree of saturation to 55%. After standing for 30 min the suspension is centrifuged for 40 min at 4200 g and the supernatant discarded. The PP-2Ac from poly(L-lysine)-Sepharose is purified in an identical manner to PP-Ic.