Effect of zinc on the Stokes' radius of metallothionein

Apothionein was prepared from rat liver metallothionein-II. To this, zinc, as zinc acetate, was re-added in a stepwise fashion to yield a series of complexes with ratios of metal to protein varying from 1:1 to 7:1. The Stokes' radius of the apoprotein and each zinc-metallothionein complex was then determined by gel filtration. A plot of atoms Zn/mol metallothionein versus Stokes' radius yielded a sigmoid curve, with values for Stokes' radius ranging from 20.8 A for the apoprotein 15.4 A for the fully saturated zinc complex.