Biogenesis of Chromaffin Granules: Incorporation of Sulfate into Chromogranin B and into a Proteoglycan |
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Authors: | G Falkensammer R Fischer-Colbrie H Winkler |
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Institution: | Department of Pharmacology, University of Innsbruck, Innsbruck, Austria |
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Abstract: | The incorporation of 35S]sulfate into the soluble proteins of chromaffin granules was studied. Isolated bovine chromaffin cells were pulse-labeled with 35S]sulfate. The radioactively labeled products were characterized by one- and two-dimensional electrophoresis. Three proteins of chromaffin granules were preferentially labeled. One was identified by immunoprecipitation as chromogranin B (Mr 100,000). This result explains why during cellular synthesis the chromogranin B precursor is converted into a significantly more acidic protein. During chase periods, the newly synthesized chromogranin B was progressively degraded by endogenous proteases. A second labeled protein, much less labeled than chromogranin B, was identified as chromogranin A. The largest portion of the radioactive label was found in a heterogeneous component (Mr 86,000-100,000; pI 4.3-5.0). Digestion experiments with chondroitinase ABC demonstrated that this labeled component and a comigrating Coomassie Blue-stained spot were selectively degraded by this enzyme. This establishes that this component is a proteoglycan. |
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Keywords: | Chromaffin granules Chromogranin A Chromogranin B Proteoglycan Sulfate incorporation |
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