Physical and Chemical Studies on Ceruloplasmin

Abstract The survival time in plasma of incompletely desialylated ceruloplasmin, labeled with 64Cu or with tritium, was studied in the rat. Removal of less than 20% of the terminal sialic acid, with consequent exposure of the penultimate galactosyl residues, resulted in the rapid disappearance from the circulation of more than 50% of the injected dose. Statistical analysis of the experimental results by means of the Poisson distribution equation supports the estimate that the exposure of no more than 2 galactosyl residues is sufficient to effect prompt clearance of ceruloplasmin from the circulation. Examination of the specificity of the two neuraminidase preparations used in this study revealed that each of the enzymes possessed a preferential affinity for different sialic acid residues, although the results from each were statistically predictable. Consequently, the removal of any 2 sialic acid residues from 1 molecule of ceruloplasmin appears to be incompatible with the continued survival of that molecule in the circulation.