Biosynthesis and secretion of α1 acute‐phase globulin in primary cultures of rat hepatcytes

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Abstract
Experimental inflammation in rats led to a 7-fold increase in serum levels of .alpha.1 acute-phase globulin (.alpha.1-APG). This increase is correlated with elevated levels of translatable mRNA for .alpha.1-APG in the liver. Biosynthesis and secretion of .alpha.1-APG were studied in rat hepatocyte primary cultures. An intracellular form of .alpha.1-APG with an apparent relative molecular mass of 63,500 and a secreted form of 68,000 were found. The intracellular form of .alpha.1-APG could be deglycosylated by endoglucosaminidase H treatment indicating that its oligosaccharide chains were of the high-mannose type. The secreted form of .alpha.1-APG was not sensitive to endoglucosaminidase H, but was susceptible to the action of sialidase reflecting carbohydrate side-chains of the complex type. Pulse-chase experiments revealed a precursor-product relationship for the high-mannose and the complex type .alpha.1-APG. In the hepatocyte medium newly synthesized .alpha.1-APG was detected 30 min after the pulse. Unglycosylated .alpha.1-APG was found in the cells as well as in the medium when the transfer of oligosaccharide chains onto the polypeptide chains was blocked by tunicamycin. Tunicamycin led to a marked delay in .alpha.1-APG secretion.
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