Characterization of the binding sites for glutaraldehyde-polymerized albumin on purified woodchuck hepatocyte plasma membranes.
Highly purified woodchuck hepatocyte plasma membranes demonstrated tight specific binding to glutaraldehyde-polymerized serum albumin immobilized on Sepharose macrobeads. This phenomenon was characterized in detail and used for recognition of the plasma membrane constituents involved in binding of the albumin polymer. The hepatocyte membrane-polyalbumin interaction was found to be ligand-specific, saturable, and time-dependent. Other characteristics of a specific receptor-ligand interaction were also noted, including a dependence on the temperature, pH, and ionic strength of the binding medium. Kinetic studies revealed the presence of two classes of binding sites for glutaraldehyde-polymerized albumin on purified membranes. The sites mediating the saturable high-affinity binding of polymer to hepatocyte membranes could not be solubilized by Triton X-100. Binding activity of Triton-insoluble membrane residues was inhibited by heat treatment and proteolysis, and was significantly suppressed by neuroaminidase digestion. These findings suggest a glycoprotein nature for the high-affinity binding sites and indicate that the corresponding receptors apparently are tightly associated with the plasma membrane matrix. In contrast, low-affinity binding of polymeric albumin was inhibited by both Triton X-100 and pronase, was resistant to neuraminidase, and was activated by lipase, suggesting that membrane lipids are important for the binding conduct. In conclusion, these results provide clear evidence that hepatocyte plasma membranes are endowed with at least two classes of chemically distinct binding components, which are able to specifically recognize serum albumin artificially modified by glutaraldehyde treatment. Therefore, they suggest that in vivo hepatocytes may perform a specific receptor-dependent uptake of ligands expressing glutaraldehyde-polymerized albumin specificity. This phenomenon may play an important role in the proposed participation of naturally modified human serum albumin as a bridge in the attachment and penetration into host hepatocyte of hepatitis B virus, which is known to possess a receptor that is specific for glutaraldehyde-cross-linked human serum albumin.
Michalak
T I
TI
Faculty of Medicine, Memorial University of Newfoundland, St. John's, Canada.
Bolger
G T
GT
D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D005976:Glutaral; D006863:Hydrogen-Ion Concentration; D007457:Iodine Radioisotopes; D008099:Liver / Q000378:metabolism / Q000648:ultrastructure; D008392:Marmota; D011092:Polyethylene Glycols / Q000494:pharmacology; D011108:Polymers; D011402:Pronase / Q000494:pharmacology; D012709:Serum Albumin / Q000378:metabolism*; D013696:Temperature
D007457:Iodine Radioisotopes; D011108:Polymers; D012709:Serum Albumin; D011092:Polyethylene Glycols; D011402:Pronase; D005976:Glutaral