Low temperature magnetic susceptibility of ceruloplasmin

The magnetic susceptibility of both ceruloplasmin and its apoprotein was measured in the temperature range from 2 to 4·2°K and at 77°K. The paramagnetic contribution of the cupric ions of ceruloplasmin to the susceptibility obeys the Curie law above 2°K. By combining the Curie constant with published electron spin resonance data, we conclude that 0·44±0·02 of the total copper in the protein is in the cupric, paramagnetic state. © 1967.