Nitric oxide regulates vascular tone by elevating smooth muscle cell cGMP levels. Activation of cGMP-dependent protein kinase (PKG) results in the lowering of intracellular Ca2+ levels producing relaxation. Previous studies have shown that PKG stimulates the calcium- activated K+ channel by dephosphorylation. To further understand the mechanism of the effects of PKG on cell function, we examined the phosphorylation of the B' γ subunit of protein phosphatase 2A (PP2A) by PKG The B' γ subunit was expressed in E.coli and purified on a Ni-NTA resin column. The eluted protein was phosphorylated using PKG and the catalytic subunit of cAMP-dependent protein kinase (PKA) in vitro. The results demonstrated that the B' γ subunit is phosphorylated in a time-dependent fashion by both PKG and PKA upto a stoichiometry of 1.8 mol of phosphate/mol of the protein. Using comparable amounts of PKG and PKA kinase activity, PKG catalyzed maximal phosphorylation within 2 min, whereas PKA catalyzed maximal phosphorylation in 10 min. These results suggest that the regulation of PP2A activity may occur through the phosphorylation of the B' γ subunit.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology