Binding and processing of 125I-ACTH by isolated rat splenic lymphocytes

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The effect of incubation temperature and ligand competition was tested for 125I-ACTH binding to isolated rat lymphocytes. αMSH but not Agouti-like peptide was an effective competitive inhibitor for cell surface binding at 4°C. Cells incubated with 125I-ACTH at 37°C rapidly associated ligand for 10 min and then gradually lost the radioactivity with time. Cells incubated with 125I-ACTH at 4°C accumulated ligand to only about half the maximal amount when compared to cells incubated at 37°C for 10 min. Temperatures below 20°C and toxins that block lysosomal degradation blocked the loss of cell-associated radioactivity. These results suggest the lymphocyte ACTH receptor is the Melanocortin 5 receptor and the receptor is internalized by endocytosis to deliver ligand to the lysosome.

Original languageEnglish (US)
Pages (from-to)542-546
Number of pages5
JournalBiochemical and Biophysical Research Communications
Issue number2
StatePublished - Dec 20 1999

Bibliographical note

Funding Information:
The author extends heartfelt gratitude to Dr. Jeffery Tatro (Department of Endocrinology, New England Medical Center Hospital, Boston, MA) for his helpful suggestions and insight during discussions leading to the choice of AGLP as a competitor to ACTH binding. This study was funded by a grant-in-aid provided by the Graduate School of the University of Minnesota.


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