regulating PP1 (protein phosphatase-1) in muscle + liver

epinephrine/adrenalin

in muscle

PKA phosphorylates GM regulatory subunits

• phosphorylated GM prevents PP1 from associating w/ its substrate → PP1 cannot dephosphorylate them

• unphosphorylated GM allows PP1 to associate w/ substrate and dephosphorylate them

PKA phosphorylates inhibitory proteins of PP1 (inhibit PP1 activity)

in liver

when glucose is low:

• inactive PP1 associates w/ phosphorylated phosphorylase A (R-state) on G_L protein

• interaction of R-state phosphorylase A inhibits PP1 activity

when glucose is high:

• glucose induces transition in phosphorylated phosphorylase A from R → T state

• inactive PP1 disociates and becomes active → can dephosphorylate its substrates

• overall: glycogen synthesis stimulated

what is PP1

dephosphorylates:

• phosphorylase kinase

• glycogen phosphorylase

• glycogen synthase

PP1 inhibited/not associated w/ substrate (muscle)

all respective enzymes phosphorylated:

• phosphorylase kinase: active

• glycogen phosphorylase (a-form): active

• glycogen synthase (b-form): inactive

glycogen synthesis inhibited, glycogen degredation stimulated