ADP‐ribosylation of phosphorylase kinase and block of phosphate incorporation into the enzyme

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Abstract
Phosphorylase kinase purified from rabbit skeletal muscle was ADP-ribosylated by hen liver nuclear ADP-ribosyltransferase. This modification, as was seen in cAMP-dependent phosphorylation, was observed only in .alpha. and .beta. subunits of the phosphorylase kinase and the latter was more rapidly modified. Analysis of the ADP-ribosylated amino acid residue sequenced in .alpha. and .beta. subunits showed that both subunits were modified at the area of the arginine residue. The Km for NAD was 0.10 mM and the pH optimum was 9.0. When the ADP-ribosylated phosphorylase kinase was phosphorylated by cAMP-dependent protein kinase, a reduction in phosphate incorporation occurred with increase in the ADP-ribosylation. ADP-ribosylation also suppressed autophosphorylation, to a lesser degree than observed with cAMP-dependent phosphorylation. The ADP-ribosylation-dependent reduction of phosphorylation resulted in a suppression of the phosphorylation-dependent activation of the phosphorylase kinase. These results together with findings of ADP-ribosyltransferase activity in the rabbit skeletal muscle [Soman, G. et al., 1984] suggest that ADP-ribosylation participates in the regulation of the phosphorylase kinase activity through changes in the rate of phosphorylation.