Glycogen phosphorylase b and phosphorylase kinase binding to glycogen under molecular crowding conditions. Inhibitory effect of FAD

Dynamic light scattering was used to study the interaction of phosphorylase kinase (PhK) and glycogen phos-phorylase b (Phb) from rabbit skeletal muscle with glycogen under molecular crowding conditions arising from the presence of 1 M trimethylamine N-oxide and at physiological ionic strength. The mean value of hydrodynamic radius of the initial glycogen particles was 52 nm. Crowding stimulated Phb and PhK combined binding on glycogen particles. Two-stage character of PhK binding to glycogen particles containing adsorbed Phb was found in the presence of the crowding agent. At the initial stage, limited size particles with hydrodynamic radius of ∼220 nm are formed, whereas the second stage is accompanied by linear growth of hydrodynamic radius. Flavin adenine dinucleotide (FAD) selectively inhibited PhK binding at the second stage. The data indicate that in the first stage Phb is involved in PhK binding by glycogen particles containing adsorbed Phb, whereas PhK binding in the second stage does not involve Phb.