title: Identical NH2-terminal amino acid sequence of the intrahepatic precursor and the secreted form of rat alpha 1-acid glycoprotein.
abstract: Automated Edman degradation of alpha 1-acid glycoprotein from serum (serum AGP) was successful only after the desialylated, reduced, and alkylated protein had been treated with pyroglutamate aminopeptidase. The sequence is (less than Glu)-Asn-Pro-Glu-Pro-Ala-X-Ile-Thr-Leu-Gly-Ile-Pro-Ile-. For radioactive sequencing of the NH2 terminus of the intracellular precursor form (liver AGP) of serum AGP, protein was labeled by incubating liver cells in suspension with either [3H]proline or [3H]isoleucine for a 15-min period. Liver AGP was separated from serum AGP by ion exchange chromatography. Between 78 and 90% of the radioactivity incorporated into total AGP was associated with liver AGP, indicating that little conversion of newly synthesized liver AGP to serum AGP had occurred during the 15-min incubation period. Liver AGP was then isolated by immunoprecipitation. The antigen-antibody complex was exposed to 15 Edman degradation cycles; however, no radioactivity was released. Automated Edman degradation of liver AGP which had been extracted from the immunoprecipitate with dilute acid and subsequently treated with pyroglutamate aminopeptidase yielded a sequence of proline and isoleucine identical with that in serum AGP. We conclude that processing of the intracellular precursor form of AGP does not involve a proteolytic trimming near the NH2 terminus.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D008099:Liver / Q000378:metabolism*; D008297:Male; D009961:Orosomucoid / Q000096:biosynthesis*; D011498:Protein Precursors / Q000096:biosynthesis*; D011865:Radioisotope Dilution Technique; D051381:Rats; D014316:Tritium
chemical_list: D009961:Orosomucoid; D011498:Protein Precursors; D014316:Tritium