Effects of metal cations on coacervation of alpha-elastin.

The quasi-elastic light scattering studies were carried out to investigate effects of metal cations such as Ca2+ and Na+ on the early stage of coacervation process of alpha-elastin, a chemical fragmentation product originated from the biological elastomeric protein elastin, in aqueous solutions. In particular, our attention was focused on changes of two types of dynamical behaviors found in the earlier work, which are a remarkable increase and a monotonous decrease in the hydrodynamic radius R of molecules with temperature for critical and off-critical concentrations of alpha-elastin, respectively. For the critical alpha-elastin concentration, an addition of Ca2+ was found to exert little effects on the steep temperature profile of R observed in the absence of Ca2+. On the other hand, an addition of a slight amount of Na+ resulted in a monotonous decrease in R, but its further addition restored a remarkable increase in R similar to the critical behaviors in the salt-free system. In the case of off-critical sample, the addition of either Ca2+ or Na+ above a certain concentration induced a change in R from a monotonous decrease to a remarkable increase. For both critical and off-critical concentrations of alpha-elastin, Ca2+ and Na+ brought about an elevation and a lowering of the temperature at which the sample started to be turbid, respectively.