Effects of osmolytes under crowding conditions on the properties of muscle glycogen phosphorylase b.

The study of the relationship between the activity and stability of enzymes under crowding conditions in the presence of osmolytes is important for understanding the functioning of a living cell. The effect of osmolytes (trehalose and betaine) on the secondary and tertiary structure and activity of muscle glycogen phosphorylase b (Ph b) under crowding conditions created by PEG 2000 and PEG 20000 was investigated using dynamic light scattering, differential scanning calorimetry, circular dichroism spectroscopy, fluorimetry and enzymatic activity assay. At 25 °C PEGs increased Ph b activity, but PEG 20000 to a greater extent. Wherein, PEG 20000 significantly destabilized its tertiary and secondary structure, in contrast to PEG 2000. Trehalose removed the effects of PEGs on Ph b , while betaine significantly reduced the activating effect of PEG 20000 without affecting the action of PEG 2000. Under heat stress at 48 °C, the protective effect of osmolytes under crowding conditions was more pronounced than at room temperature, and the Ph b activity in the presence of osmolytes was higher in these conditions than in diluted solutions. These results provide important insights into the complex mechanism, by which osmolytes affect the structure and activity of Ph b under crowding conditions. • PEG 2000 and especially PEG 20000 destabilized structure of Ph b and increased its enzymatic activity. • Trehalose completely removed destabilizing effects of both PEGs but betaine only partialy • When heated in the presence of osmolytes, Ph b activity under crowding conditions was higher than in dilute solutions. • Protective effect of osmolytes under crowding conditions was most noticeable under heat stress. [ABSTRACT FROM AUTHOR]