The Presence of Zinc in Human Cytocuprein and Some Properties of the Apoprotein

Purified cytocuprein from human liver, brain, and erythrocytes was found to contain near 2 g atoms of zinc per mole of protein. Both the copper and zinc were strongly bound and only relatively small amounts of them could be removed from the protein by dialysis against EDTA and 1,10-phenanthroline under various conditions. Virtually all of the metal was removed by treatment with potassium cyanide at neutral pH. There appeared to be very little change in the tertiary structure of the protein upon removal of the metal. This was indicated by the observations that the velocity and equilibrium sedimentation properties, the immunological properties, and absorption in the 200 to 240 mµ range of the native and apoprotein are similar. However, such treatment resulted in a diminution in the intensity of absorption of cytocuprein between 240 and 400 mµ and the disappearance of the broad absorption peak with a maximum near 675 mµ.