Characterisation of two protein phosphatase 2A holoenzymes from maize seedlings

Two holoenzymes of protein phosphatase 2A (PP2A), designated PP2AI and PP2A II, were purified from maize seedlings. The subunit composition of maize ho loenzymes generally resembled those of animal PP2A. Using SDS/PAGE and West ern blots with antibodies generated against peptides derived from animal PP 2A, we established the subunit composition of plant protein phosphatase 2A. In both maize holoenzymes, a 38 000 catalytic (PP2Ac) and a 66 000 constan t regulatory subunit (A) constituting the core dimer of PP2A were present. In addition, PP2AI (180 000-200 000) contained a protein of 57 000 which re acted with antibodies generated against the peptide (EFDYLKSLEIEE) conserve d in all eukaryotic B alpha regulatory subunits. In contrast, none of the p roteins visualised in PP2AII (140 000-160 000) by double staining reacted w ith these antibodies. The activity of PP2AI measured with P-32-labelled pho sphorylase a in the presence of protamine and ammonium sulfate is about two times higher than that of PP2AII. PP2AI and PP2AII displayed different pat terns of activation by protamine, polylysine and histone H1 and exhibit hig h sensitivity toward inhibition by okadaic acid. The data obtained provide direct biochemical evidence for the existence in plants of PP2A holoenzymes composed of a catalytic subunit complexed with one or two regulatory subun its. (C) 2000 Elsevier Science B.V. All rights reserved.