| Autor: |
J. D. Etlinger, R. M. Carriere, R. A. Janeczko |
| Rok vydání: |
1985 |
| Předmět: |
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| Zdroj: |
Journal of Biological Chemistry. 260:7051-7058 |
| ISSN: |
0021-9258 |
| DOI: |
10.1016/s0021-9258(18)88886-x |
| Popis: |
The endocytic activity of chick myotubes in cultures was investigated. Differentiated myotubes internalized the fluid-phase marker horseradish peroxidase in membrane-bound particles which typically displayed reaction product at the inner surface of the vesicle. Pulse-chase experiments demonstrated a rapid decrease in the number of horseradish peroxidase-containing vesicles and a redistribution from a uniform to a perinuclear pattern. Horseradish peroxidase uptake was extensively inhibited by incubation at 0-4 degrees C consistent with an endocytic mechanism. To further characterize the process, the fate of labeled protein was investigated. Following uptake [3H] hemoglobin A was extensively degraded (40-50%) to acid-soluble products within 10 h. Degradation displayed a biphasic pattern with a rapid early phase followed by a much slower second phase. The decreasing rate of proteolysis can be accounted for, in part, by a simultaneous exocytosis of a substantial fraction (25-30%) of acid-insoluble label from myotubes. The lysosomotropic agents methylamine, monensin, and chloroquine significantly inhibited (23-75%) proteolysis, indicating a lysosomal site of degradation. Part of the inhibitory effect results from an increase in exocytosis in the presence of these agents. Degradation of endocytosed [3H]hemoglobin A was not inhibited by insulin. In contrast degradation of endogenous myotube proteins was inhibited (40%) by insulin and blocked by methylamine. These results suggest that cultured myotubes possess a coupled endocytic/exocytic pathway for macromolecules and that a fraction of the internalized substrate is degraded by an insulin-insensitive lysosomal pathway. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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