Internalization and degradation of iodinated OPG in CAG cells.

(A) Cells were labeled with ¹²⁵I-OPG on ice, washed, and chased by incubation in medium at 37°C as indicated. Heparin-resistant, cell-associated OPG (●) and TCA-soluble radioactivity in cell supernatants (○) were measured as described in “Patients, materials, and methods.” The triangle indicates OPG bound to the cells before the chase period. (B) Polyacrylamide gel electrophoresis of cell pellets containing ¹²⁵I-OPG. The cells were incubated at 37°C for the indicated time periods in the presence or absence of NH₄Cl after labeling on ice. The arrows indicate the position of intact OPG dimers.