Effect of ionic strength and arginine on aggregation of UV-irradiated muscle glycogen phosphorylase b

In this work the effect of ionic strength and arginine on the kinetics of aggregation of UV-irradiated muscle glycogen phosphorylase b (UV-Phb) was studied using dynamic light scattering at 37 °C at various ionic strengths (0.02-0.7 M). Under these conditions the rate-limiting stage of the overall aggregation process is the structural reorganization of UV-Phb, which can be characterized by the first order rate constant k_I. It was shown that an increase in NaCl concentration caused a decrease in the k_I value, suggesting a slowdown of the UV-Phb structural reorganization. Circular dichroism data confirmed this conclusion. Arginine is widely used in biotechnology as an agent suppressing protein aggregation. However, arginine is a charged molecule, and, when studying the action of arginine on protein aggregation, the effects of ionic strength should be taken into account. To evaluate the effect of arginine, experiments were conducted at fixed values of ionic strength (0.15 M and 0.5 M). It was shown that at a low ionic strength arginine (0-0.13 M) accelerated the process of protein aggregation, whereas at higher ionic strength arginine (0-0.48 M) acted as an aggregation suppressor.