Biosynthesis and processing of pro‐C3, a precursor of the third component of complement in rat hepatocytes: effect of secretion‐blocking agents

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Abstract
Biosynthesis and intracellular processing of the third component (C3) of complement were studied in cultured rat hepatocytes. In the control cells, the complement C3 was synthesized as a pro‐form, a single polypeptide chain comprising both the α‐ and β‐subunits. Although the cleavage of the pro‐form into the subunits was not clearly demonstrable within the cells during pulse‐chase periods, all the secreted C3 was the mature processed form. The cells were treated with secretion‐blocking agents with different modes of action, colchicine and monensin. Colchicine caused an accumulation of the processed C3 within the cells, whereas monensin blocked the secretion without a significant accumulation of the processed form. The results indicate that the conversion of the C3 pro‐form into the subunits takes place in the secretory vesicles just before the secretion.