Studies on the state of copper in native and modified human ceruloplasmin.

Several experiments reported in the preceding paper (1) have indicated that not all the copper atoms of human ceruloplasmin are present in the same state within this molecule. Furthermore, acid-base titrations of ceruloplasmin have shown distinct regions of instability. The absorbancy changes noted in the 610-rnp range during these titrations indicated the involvement of the chromophoric copper atoms. It was of interest to correlate some of the results of physicochemical studies with those obtained by methods more specifically designed to evaluate the copper constituent of ceruloplasmin. The studies utilized copl)er-chelating agents, methods for the analysis of total copper and of cuprous copper, and election paramagnetic resonance spectroscopy. Measurements were made of the changes in optical absorption and in the well known osidase activity of ceruloplasmin and were correlated with the results of the copper analyses on similarly treated protein.