Interaction of mature, unglycosylated and cell-free synthesized rat alpha 1-proteinase inhibitor with elastase.

Purified rat alpha 1-proteinase inhibitor (Mr 54 000) and porcine pancreatic elastase (Mr 26 000) formed a complex (Mr 82 000) resistant to heat treatment under denaturing and reducing conditions. A similar alpha 1-proteinase-inhibitor-elastase complex was detected by immunoprecipitation of alpha 1-proteinase inhibitor from the medium of [35S]methionine-labeled hepatocyte primary cultures after incubation with elastase. Treatment of hepatocytes with tunicamycin led to the secretion of an unglycosylated alpha 1-proteinase inhibitor (Mr 41 000) which also formed a complex with elastase (Mr 66 000). Complex formation (Mr 68 000) could also be observed between cell-free synthesized pre-alpha 1-proteinase inhibitor (Mr 43 000) and elastase (Mr 26 000). The results suggest that neither glycosylation nor removal of the signal peptide are required for the formation of a biologically active conformation of alpha 1-proteinase inhibitor.