Summary
In mice liver plasma membranes (PM), the binding affinity of receptors for [125I] human growth hormone (hGH) was dependent on the association time: after 18 hours,
a high affinity receptor form with KA = 6.8 × 109M-1 accumulated and, as compared to after 1 hour, an increase up to 88%, in a slow dissociating
component was observed. Preincubation of PM with concanavalin A (Con A) or other lectins
from Lens culinaris (LCA), Ricinus communis (RCA I), Wheat germ agglutinin (WGA) specifically
inhibited the binding of hGH to receptors by 54, 28, 50 and 25%, respectively. Furthermore,
PM pretreatment with Con A concomitantly increased the rate of dissociation of the
hormone-receptor (H-R) complex to 92 or 65% after association for 1 or 18 hours. These
Con A-induced alterations resulted from a reduced fraction of the slow dissociable
component together with an increased rate constant. The treatment of PM with Con A
subsequent to incubation with the hormone did not decrease hormone binding but caused
the conversion of the class of hGH receptors exhibiting fast dissociation kinetics
towards a form exhibiting slow ones. These data strongly suggest a role for glycoproteins
of the N-acetyllactosaminic type in the affinity state of liver membrane hGH receptors.
Key-Words
Human Growth Hormone Receptor Affinity
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Liver Plasma Membranes
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Concanavalin A
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Glycoproteins