Specific receptor for ceruloplasmin in membrane fragments from aortic and heart tissues

Membrane fragments from aortic and heart tissues of immature chicks were observed to bind highly purified, 125I-labeled chick ceruloplasmin. The binding reaction exhibited a linear Scatchard plot for both tissues and showed for each an apparent dissociation constant (Kd) of about 10(-8) M. On the basis of Scatchard analyses, aorta contained 1.5 pmol of receptors/mg of membrane protein, whereas receptors in the membranes from heart tissue were at least 5 times more dense. The binding of chick ceruloplasmin to aorta membranes was trypsin sensitive and neuraminidase insensitive, and showed both saturation and reversibility. Various sialoglycoproteins in 500 molar excess had very little effect on the binding. The asialo derivatives of these proteins likewise did not inhibit the binding. Human ceruloplasmin was found to bind very weakly to the chick membranes. Asialo chick ceruloplasmin bound with the same efficacy as native chick ceruloplasmin. Heat-denatured chick ceruloplasmin, however, was very ineffectual in displacing native 125I-ceruloplasmin from the membranes. These studies provide the first evidence for a homologous membrane receptor for native ceruloplasmin in the plasma membranes of animal cells.