PURIFICATION OF TYPE-1 PROTEIN (SERINE THREONINE) PHOSPHATASES BY MICROCYSTIN-SEPHAROSE AFFINITY-CHROMATOGRAPHY/

A microcystin (MC)-Sepharose column was prepared by addition of 2-amin oethanethiol to the alpha,beta-unsaturated carbonyl of the N-methyldeh ydroalanine residue of MC-LR, followed by reaction of the introduced a mino group with N-hydroxysuccinimide-activated CH-Sepharose. The MC-Se pharose bound protein phosphatase-1 (PP1) with high capacity and purif ied human PP1 gamma in one step from E, coli extracts. It was also use d to purify forms of PP1 bound to myofibrils from skeletal muscle. Two of these comprised PP1 complexed to N-terminal fragments of the M-sub unit which enhance its myosin phosphatase activity, while the third co mprised PP1 and an N-terminal fragment of the glycogen-binding (G)-sub unit.