The binding of Zinc by S-Carboxymethyl Kerateine 2 from wool

Abstract

The binding of zinc from zinc acetate solution by the S-carboxymethyl derivative of kerateine 2 (SCMK2), a soluble protein extracted from reduced wool, has been studied by the method of equilibrium dialysis over the pH range 5.5 to 8.0 using radioactive ⁶⁵Zn to determine the zinc concentration. The binding increases as the pH increases from 5.5 to 7.5. The extent of binding is also a function of free zinc concentration, but it is not affected by changes in ionic strength between 0.15 and 1.0. The difference in solubility between the zinc complexes of the two protein components of SCMK2 is probably not due to the differences in the amount of zinc bound. The binding of zinc is reversible over the concentration range studied at both pH 6.0 and 7.5, and its removal is accelerated by treatment with chelating agents. Over the pH range 6.0 to 7.5 more zinc is bound by this protein than can be accounted for by histidine binding alone, assuming a 1 : 1 zinc-histidine ratio.