Phosphoprotein phosphatase and

Increases in cAMP further lead to phosphorylation and activation of phosphoprotein phosphatase inhibitor 1 (PPl-1), which inhibits the activity of phosphoprotein phosphatase and so decreases the conversion (dephosphorylation) of inactive to active HMG-CoA reductase. 

A great deal more needs to be known about these important phosphoprotein phosphatases and the in vivo role they may play in the regulation of cellular activity and phosphate turnover. An immobilized enzyme system for the phosphorylation of proteins has been described (108a). 

Figure 11.16 Regulation of glycogen phosphorylase by phosphorylation/dephosphorylation The major enzymatic system in the regulation of glycogen phosphorylase (i.e. phosphorylase) by the multicyclic phosphorylation/dephosphorylation cascade is shown. Abbreviations used are Pr, protein PrK, Protein kinase phosphorylaseK, phosphorylase kinase (C2R2 where C2 and R2 are dimeric catalytic and regulatory subunits respectively) PPrP, phosphoprotein phosphatase (G), G-subunit of phosphoprotein phosphatase and p-(G), phopsho-G-subunit.

---