Human erythrocyte Mn2+-dependent (C'A') and -independent (CA) protein-serine/threonine phosphatase (PP) 2A are composed of 34-kDa catalytic C' and C subunits, in which the metal dependency resides, and 63-kDa regulatory A' and A subunits, respectively. Each catalytic and regulatory subunit gave the same V8- and papain-peptide maps, respectively. Stoichiometric zinc and substoichiometric iron were detected in CA but not in C'A'. The Mn2+-dependent protein-tyrosine phosphatase (PTP) activity of C'A' was about 70-fold higher than that of CA. Pre-incubation of CA with 25 mM NaF changed CA to a Mn2+-dependent form with higher PTP activity. The same NaF treatment had no effect on C'A'. Pre-incubation of C'A' with ZnCl2, zinc-metallothionein, or FeCl2 activated the Mn2+-independent PP activity, but pre-incubation with FeCl3 did not. Ascorbate in the pre-incubation and assay mixture significantly stimulated the effect of FeCl2. Pre-incubation of C'A' with 5 μM ZnCl2 and 15 μM FeCl2 in the presence of 1 mM ascorbate synergistically stimulated the Mn2+-independent PP activity, with concomitant suppression of the Mn2+ -dependent PP and PTP activities. The PP and PTP activities of CA were unaffected by the same zinc and/or iron treatment. Micromolar concentrations of vanadate strongly inhibited the Mn2+-dependent PP activity of C'A' but only slightly inhibited the PP activity of CA. Using the distinct effect of vanadate as an indicator, the interconversion between CA and C'A' with the above mentioned treatments was proved. These results support the notion that Mn2+-independent CA is a Zn2+- and Fe2+-metalloenzyme, whose apoenzyme is Mn2+-dependent C'A'.
|Number of pages||7|
|Journal||Journal of biochemistry|
|Publication status||Published - 1999 Jan 1|
- Protein phosphatase 2A
- Zinc- and iron-metalloenzyme
ASJC Scopus subject areas
- Molecular Biology