Microcystin affinity purification of plant protein phosphatases: PP1C, PP5and a regulatory A-subunit of PP2A

Proteins of similar to 35, 55 and 65 kDa were purified from cauliflower ext racts by microcystin-Sepharose chromatography and identified by amino acid sequencing as plant forms of protein (serine/threonine) phosphatase 1 (PP1) catalytic subunit, PP5 and a regulatory A-subunit of PP2A, respectively. P eptides that corresponded both to the tetratricopeptide (TPR) repeat and ca talytic domains of PP5 were identified. Similar to mammalian PP5, the casei n phosphatase activity of plant PP5 was activated > 10-fold by arachidonic acid, with half-maximal stimulation occurring at similar to 100 mu M lipid (C) 1999 Federation of European Biochemical Societies.