Interaction of human fibrinogen with divalent metal chlorides

Precipitation of human fibrinogen in 0.15 m NaCl occurred at pH 7.4 (Tris-HCl buffer) when ZnCl₂, CuCl₂, NiCl₂, or CoCl₂ were added beyond their respective critical concentrations. The critical concentrations were about $\text{4 × 10}{}^{\mathrm{?5}}\text{m}\text{ZnCl}{}_2\text{, 6 × 10}{}^{\mathrm{?5}}\text{m}\text{CuCl}{}_2\text{, 3 × 10}{}^{\mathrm{?4}}\text{m}\text{NiCl}{}_2\text{and}\text{1 × 10}{}^{\mathrm{?3}}\text{m}\text{CoCl}{}_2$. At pH 5.8 2-(N-morpholino)-ethane sulphonic acid buffer, the critical concentrations were found only for CuCl₂ and ZnCl₂, and were about $\text{3 × 10}{}^{\mathrm{?5}}\text{and}\text{3 × 10}{}^{\mathrm{?4}}\text{m}$, respectively. CaCl₂ and MgCl₂ were not effective up to $\text{1 × 10}{}^{\mathrm{?2}}\text{and}\text{2 × 10}{}^{\mathrm{?2}}\text{m}$ at pH 7.4 and 5.8, respectively. At pH 7.4, precipitation was better in 0.015 m NaCl than in 0.15 m NaCl for both CuCl₂ and ZnCl₂. Little or no conformational change was indicated on binding Cu²⁺ ions. The fluorescence of tryptophan was quenched only by CuCl₂, while other metal ions (ZnCl₂, NiCl₂, CoCl₂ and CaCl₂) were ineffective as quenchers.