Activation of Protein Phosphatase 1

Protein Phosphatase 2A Inhibitors, I1PP2A and I2PP2A, Associate with and Modify the Substrate Specificity of Protein Phosphatase 1

“…Consistent with earlier observations (24,33), the recombinant preparations of PP1 C were dependent on Mn 2ϩ for their activity with phosphorylase as substrate (Table I). In addition, the skeletal muscle preparations were inhibited about 60% by 1 mM Mn 2ϩ with this substrate (Table I).…”

“…This conversion to a Mn 2ϩ -dependent state can also occur spontaneously during the purification or storage of these enzymes. For example, Chu et al (24) recently purified to homogeneity a Mn 2ϩ -dependent form of PP1 C from cardiac myofibrils. X-ray crystallography of recombinant PP1 C indicates that Mn 2ϩ replaces the site 2 metal, Zn 2ϩ , which is not incorporated when this enzyme is expressed in bacteria (39,40).…”

“…These results suggest that the acidic tails of I 1 PP2A and I 2 PP2A have little or no effect on the Mn 2ϩ -dependent stimulation of PP1 C activity. Divalent Cation Specificity-Recent studies showed that Co 3ϩ stimulates the activity of recombinant preparations of PP1 C by binding relatively tightly to the phosphatase (24 (Fig. 4B), half-maximal stimulation of the skeletal muscle and recombinant phosphatase preparations with MBP as substrate occurred at about 10 M Mn 2ϩ .…”

Effects of cations on ceramide-activated protein phosphatase 2A

“…Using a recombinant PP1 catalytic subunit, a stable metalloenzyme form of PP1 has been generated (Chu et al, 1996). It has been suggested that at least two metal binding sites exist on the enzyme and that PP1 may be an Fe 2+ /Zn 2+ metalloenzyme in vivo (Chu et al, 1996). In the present study, Zn 2+ , Fe 2+ and Cu 2+ completely inhibited and Ni 2+ and Mn 2+ partially inhibited CAPP.…”

“…Indeed, it has been shown that some, such as Mn 2+ , enhances intrinsic calcineurin phosphatase activity, while others, like Ni 2+ , Fe 2+ , Zn 2+ , and Cu 2+ , are strongly inhibitory (Gupta et al, 1990). Using a recombinant PP1 catalytic subunit, a stable metalloenzyme form of PP1 has been generated (Chu et al, 1996). It has been suggested that at least two metal binding sites exist on the enzyme and that PP1 may be an Fe 2+ /Zn 2+ metalloenzyme in vivo (Chu et al, 1996).…”