Intracellular and oligomeric forms of surfactant-associated apolipoproteins(s) A in the rat.
Sulfhydryl-dependent oligomeric forms of the surfactant-associated apolipoprotein(s) A, obtained from particulate preparations of adult rat lung lavage, were characterized by immunoblot analysis and by silver staining of proteins separated by one- and two-dimensional SDS-polyacrylamide gel electrophoresis. Under non-reducing conditions, these proteins migrated as oligomers, Mr approx. 50-70, 115, 160 kDa and greater. The large oligomers were reduced to the apolipoprotein(s) A subunits by treatment with beta-mercaptoethanol; Mr 38 (A3), 32 (A2) and 26 kDa (A1), pI 4.2-4.8. Mr 50 kDa protein was composed of sulfhydryl-dependent homo-dimers of protein(s) A1 (Mr 26 kDa). 55 kDa protein was a hetero-dimer composed primarily of A1 and A2 (Mr 26 and 32 kDa). 62 kDa protein was composed of hetero-dimers of A3 and apolipoprotein A2 (Mr 38 and 32 kDa). 70 kDa protein was a homodimer composed of apolipoprotein A3 A3 (38 kDa). Larger molecular forms were composed primarily of 38 and 32 kDa and lesser amounts of 26 kDa. Treatment with endoglycosidase F reduced A2 and A3 to 26 kDa. Apolipoprotein A1 co-migrated with a protein of Mr 26 kDa immunoprecipitated from [35S]methionine-labelled Type II epithelial cells. Chymotryptic-tryptic peptide maps of apolipoproteins A1, A2 and A3 were identical, suggesting that apolipoproteins A3 and A2 arise through extensive glycosylation of apolipoprotein A1.
D000818:Animals; D001054:Apolipoproteins A / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D006026:Glycoside Hydrolases / Q000378:metabolism; D007525:Isoelectric Focusing; D008168:Lung / Q000032:analysis*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D008856:Microscopy, Fluorescence; D008970:Molecular Weight; D011663:Pulmonary Surfactants / Q000032:analysis*; D051381:Rats; D011919:Rats, Inbred Strains; D014357:Trypsin / Q000378:metabolism
D001054:Apolipoproteins A; D011663:Pulmonary Surfactants; D006026:Glycoside Hydrolases; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D014357:Trypsin