Abstract
Surfactant apolipoprotein A (apo A) is a major lipid binding protein and an active component of pulmonary surfactant. Apo A was purified from human alveolar lavage, amniotic fluid and alveolar proteinosis fluid. Two major forms were identified by silver stain and immunoblot: apo A2 (Mr=34,000), apo A1 (Mr=28,000). Larger forms were reduced to Mr=28;000 by treatment with endoglycosidase F demonstrating complex N-linked oligosaccharide. Isoelectric point was increased by neuraminidase demonstrating presence of sialic acid. Poly A mRNA isolated from adult human lung was translated in vitro; primary translation products were identified at Mr=28,000. Homology between Mr=34,000 and 28,000 was confirmed by analysis of 2D tryptic peptide maps of apo A1 and A2 which were identical, thus providing evidence that apo A results from processing of the Mr=28,000 precursor by addition of carbohydrate. Amino acid composition of purified apo A was rich in glycine and contained a large portion of collagen-like sequence. Apoproteins A were identified in surfactant from amniotic fluid, normal adult lung lavage, human cadaver lavage and material obtained from a patient with alveolar proteinosis. Apo A was identified in all of these samples by silver stain and immunoblot analysis. Alveolar proteinosis fluid contained acidic aggregates whose peptide maps were identical to apo A from normal human lung lavage. These studies clarify the identity of human apo A, a complex N-linked glycoprotein derived from a polypeptide of Mr=28,000.
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Hull, W., Weaver, T., Ross, G. et al. 1780 HUMAN SURFACTANT ASSOCIATED APOLIPOPROTEIN A: MOLECULAR COMPOSITION AND PRIMARY TRANSLATION PRODUCTS. Pediatr Res 19, 407 (1985). https://doi.org/10.1203/00006450-198504000-01798
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DOI: https://doi.org/10.1203/00006450-198504000-01798