Characteristics of somatotropic growth hormone binding to homologous liv plasma membranes.
The binding of 125I-labeled oGH, rGH and hGH to homologous liver membranes is compared to define the characteristics of somatotropic hormone-receptor interactions. The effect of pH and cations and the time-course of binding of these different GHs was similar when binding was determined in liver membranes from the homologous species. The time-course of binding was characterized by stable binding by 90-120 min of incubation at 22 degrees C with relatively high nonspecific binding that continued to increase with time. This resulted in a peak of specific binding for each hormone. Addition of excess unlabeled hormone at 30 min of the binding incubation resulted in partial displacement of the bound GH. The binding of rGH was somewhat dependent upon the presence of divalent cations (Mg2+, Ca2+) in the incubation medium. In the absence of added divalent cation, a small but appreciable amount of binding was detected at pH 7-8. With 10 mM calcium, binding increased several-fold with a definite peak of rGH binding at pH 4-5. Both oGH and hGH exhibited a broad peak of binding at pH 5-7. Monovalent cations (Na+, K+) were either ineffective in enhancing GH binding or produced a slight enhancement at higher concentrations (100 mM). Competitive displacement curves confirm the somatotropic nature of the GH-receptor interaction. Human P1 was ineffective in competing for GH binding. We conclude that 'somatotropic' growth hormone binding to its homologous liver receptor exhibits phylogenetically consistent and distinguishing characteristics of binding.(ABSTRACT TRUNCATED AT 250 WORDS)
Hung
C H
CH
Kover
K
K
Moore
W V
WV
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D013006:Growth Hormone / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism; D011986:Receptors, Somatotropin; D012756:Sheep
D011956:Receptors, Cell Surface; D011986:Receptors, Somatotropin; D015636:Magnesium Chloride; D013006:Growth Hormone; D008274:Magnesium; D002118:Calcium