PP7, a recently identified protein Ser/Thr phosphatase of the PPP family di
stantly related to phosphatases PP5/PPT and PPEF/rdgC, was purified from ca
uliflower extracts to apparent homogeneity. Purified cauliflower PP7 and re
combinant PP7 expressed in Escherichia coli exhibit light absorption in the
visible range with a maximum at similar to 430 nm. Under nonreducing condi
tions, native PP7 exists as a mixture of monomer with an intramolecular dis
ulfide bridge, disulfide-linked homodimer, and possibly disulfide-linked co
mplexes with potential partner proteins. The activity of recombinant Arabid
opsis thaliana PP7 is reversibly regulated by redox agents. The results dem
onstrate the existence of PP7 protein in planta and suggest a possibility o
f redox regulation of this protein phosphatase. (C) 2001 Elsevier Science.