Effect of molecular crowding on self-association of phosphorylase kinase and its interaction with phosphorylase b and glycogen.

Self-association of phosphorylase kinase (PhK) and its interaction with glycogen (M=5500 kDa) and phosphorylase b (Phb) has been studied using analytical ultracentrifugation and turbidimetry under the conditions of molecular crowding arising from the presence of high concentrations of osmolytes. In accordance with the predictions of the molecular crowding theory, trimethylamine N-oxide (TMAO) and betaine greatly favor self-association of PhK induced by Mg2+ and Ca2+ and PhK interaction with glycogen. In contrast, proline suppresses these processes, probably, due to its specific interaction with PhK. All osmolytes tested prevented the complex formation between PhK and its physiological substrate, Phb. The specific interactions of PhK and Phb with glycogen, in the living cell, presumably is a factor allowing the negative effect of crowding on the recognition of Phb by PhK to be overcome.