POLAROGRAPHIC STUDY OF METAL ION COMPLEXES WITH GLOBIN. PART II. COBALT, NICKEL, ZINC, AND CADMIUM AT pH 5.0 AND 6.6

Polarograrna of Co, Ni, Zn, and Cd at various concentrations (0.0075-0.02 M) in presence of globin at pH 5.0 and at 37ºshow that the diffusion currents in presence of 1.0% globin are less than that in 0.01%, leading to the conclusion that the metal ions Form complexes with globin, the -COOH groups of which ionise between pH 2.0 and 5.5. In presence of 1.0% globin the diffusion current decreases with time and is constant after 75 minutes in case of Co, Ni, and Zn and 60 minutes in cape of Cd. The number of g. atoms of each metal combined with one g.molecule of globin has been calculated. The number of metal atoms combined with one molecule of globin is found to be 24 in the ease of Zn; 20 atoms of the bivalent metal are accounted for 40 -COOH and 4 for 8 -SH groups present in one molecule of globin. Lower values at different concentrations of other metals may be attributed to the ionisation of protein-bound metal.