Deficiency of holo-, but not apo-, ceruloplasmin in genetically copper-intoxicated LEC mutant rat.

Long-Evans Cinnamon(LEC) mutant rats exhibited less than 5% of normal levels of serum ceruloplasmin oxidase activity, but immunoblot analysis showed normal levels of immunologically detectable ceruloplasmin protein in sera from the mutant rats. Immunostaining of cryosections from the liver tissues with anti-ceruloplasmin antibody showed no significant difference between normal and LEC rats. Results from pulse labeling of ceruloplasmin for 3 hours with [35S]methionine in primary hepatocyte culture, followed by immunoprecipitation, SDS-PAGE and fluorography, showed only minor changes in ceruloplasmin protein synthesis and secretion. These results suggest that the mutation(s) does not affect ceruloplasmin gene expression, but results in a failure in the mechanism whereby copper is incorporated into newly synthesized apoceruloplasmin to produce oxidase active holoform.