Circulating proalbumin associated with a second case of antitrypsin Pittsburgh.

We report here the conclusive identification of circulating proalbumin of normal N-terminal sequence (Arg Gly Val Phe Arg Arg Asp Ala) in a second child with the alpha 1-antitrypsin Pittsburgh 358 Met-->Arg mutation. As in the first case, the proalbumin made up 3-5% of the total serum albumin. The finding of proalbumin associated with a second de novo mutation at the inhibitory site bait of antitrypsin confirms our earlier hypothesis; that antitrypsin Pittsburgh was acting as a specific intracellular inhibitor of the hepatic proalbumin convertase and that antitrypsin Pittsburgh could be used as a probe to identify the proprotein convertase.