Human hepatocytes exhibit receptors for alpha 2-macroglobulin and pregnancy zone protein-proteinase complexes.
Hepatocytes were isolated by application of the two-step collagenase technique to pieces of human liver. 125I-labelled alpha 2-macroglobulin-trypsin complex bound to hepatocytes at 4 degrees C with a half time of approximately 4.5 h. At near equilibrium half of the receptors were saturated at an alpha 2-macroglobulin-trypsin complex concentration of about 60 pmol 1(-1) and the Scatchard plot was linear. Dissociation of the labelled complex was slow (T1/2 = 24 h) at low receptor occupancies. At high receptor occupancies dissociation was biphasic with a rate constant (K-1) for the initial rapid phase of about 2.4 x 10(-2) min-1. Labelled alpha 2-macroglobulin-trypsin complex bound at 4 degrees C was rapidly internalized at 37 degrees C (T1/2 = 1.9 min), and in 3.5 h approximately 10% of the label was released into the medium in a trichloroacetic acid-soluble form. At 37 degrees C, 125I alpha 2-macroglobulin-trypsin was taken up by hepatocytes and trichloroacetic acid soluble radioactivity appeared in the medium following a sigmoidal curve. Similar results were obtained with 125I-pregnancy zone protein-chymotrypsin complex. At 4 degrees C, hepatocytes bound nearly equal amounts of labelled alpha 2-macroglobulin-trypsin and pregnancy zone protein-chymotrypsin complex, and a large excess (100 nmol 1(-1) of one of the macroglobulins could almost completely abolish binding of trace amounts (5-20 pmol 1(-1] of the other. The present findings strongly suggest that the hepatocyte is of major importance for removal of alpha 2-macroglobulin- and pregnancy zone protein-proteinase complex in humans, in agreement with previous results in rats and mice.
Petersen
C M
CM
Department of Clinical Immunology, University Hospital of Aarhus, Denmark.
Christiansen
B S
BS
Jensen
P H
PH
Moestrup
S K
SK
Gliemann
J
J
Sottrup-Jensen
L
L
Ingerslev
J
J
D001693:Biological Transport, Active; D002918:Chymotrypsin / Q000378:metabolism / Q000493:pharmacokinetics; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011257:Pregnancy Proteins / Q000378:metabolism* / Q000493:pharmacokinetics; D011971:Receptors, Immunologic / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism* / Q000493:pharmacokinetics; D000511:alpha-Macroglobulins / Q000378:metabolism* / Q000493:pharmacokinetics
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D011257:Pregnancy Proteins; D011971:Receptors, Immunologic; C028939:alpha-2-macroglobulin-trypsin complex; D000511:alpha-Macroglobulins; D002918:Chymotrypsin; D014357:Trypsin