N-terminal amino acid sequences of precursor and mature forms of alpha-1-antitrypsin

alpha-1-Antitrypsin is found in hepatocytes as a high-mannose glycoprotein (Mr 49 000), extracellularly as a complex-type glycoprotein (Mr 54 000). Deglycosylation of both forms with peptide: N-glycosidase led to proteins of identical app. Mr (41 000). The sequence of 26 N-terminal amino acids of rat alpha 1-antitrypsin was determined. A high content of polar amino acids was found. The partially characterized presequence of in vitro synthesized alpha 1-antitrypsin showed a cluster of hydrophobic amino acids. A pre-peptide of 24 amino acids is proposed. There is no evidence for the existence of a propeptide.