Identification of an apoceruloplasmin-like substance in the plasma of copper-deficient rats.

Male Sprague-Dawley rats were raised on a copper-deficient diet for 4 weeks. At that time their plasma contained little or no ceruloplasmin oxidase activity but did form a precipitate with a rabbit antibody to rat ceruloplasmin. Immunoelectrophoresis of plasma from copper-deficient rats revealed that the substance precipitating with the anticeruloplasmin antibody had the same properties as apoceruloplasmin. In addition, partial purification of the substance indicated that it contained less than 10% of the copper content of holoceruloplasmin. Quantitative precipitin assays of rat plasma showed that the apoceruloplasmin-like substance was present in a concentration equivalent to 25% of the ceruloplasmin concentration in control rats raised on a regular diet. The intraperitoneal injection of copper to the copper-deficient rats resulted in restoration of normal plasma concentrations of ceruloplasmin within 24 to 48 hours.