Partially phosphorylated glycogen phosphorylase in the lugworm Arenicola marina, its regulatory function during...

Glycogen phosphorylase (GPase) from the body wall of the lugworm Arenicola marina (Annelida, Polychaeta) probably exists as a phospho-dephospho hybrid (GPase ab). The hybrid was identified by phosphorylation of purified lugworm GPase b (unphosphorylated form) with rabbit muscle GPase kinase and [gamma-32P]ATP. The completeness of phosphorylation was checked on DEAE-Sephacel. Only one GPase form was eluted. Its 32P incorporation was determined to 0.52 +/- 0.08 mol 32P/100,000 x g protein (n = 4). This GPase ab produced by in vitro phosphorylation has shown similar dependences on AMP and caffeine as GPase extracted from the body wall of the lugworm. Its reversible conversion with endogenous phosphatase and kinase to GPase b has also been demonstrated while a completely phosphorylated form (GPase a) was not detected neither in vivo nor in vitro. Lugworm GPase ab has shown a 2.4-fold higher specific activity as GPase b. The Km for P(i) was 16 mmol/l in absence and 13 mmol/l in presence of AMP. Half maximum activation by AMP was reached at 9 mumol/l. IMP up to 10 mmol/l did not activate and ATP up to 4 mmol/l did not inhibit GPase ab in absence of AMP.