Evidence for Intracellular Transport of Radioactive Protein in Alveolar Cells

Abstract

HISTOCHEMICAL studies have suggested that the acellular lining layer of pulmonary alveoli as well as the cytoplasmic inclusions (laminar bodies) of alveolar cells contain carbohydrate–protein moieties^1–3. These findings led me to investigate the subcellular site of incorporation of D-glucosamine-1-¹⁴C by alveolar cells induced by M. bovis (B.C.G.⁴). This designation does not imply that these cells are type II granular pneumocytes, but rather that they originate predominantly from cells that line normal alveoli⁵. The kinetics⁶ of the subcellular distribution of radioactivity in cells which have been pulso labelled with glucosamine-1-¹⁴C suggest attachment of glucosamine to protein at the microsomal level followed by transfer of the labelled protein to particles which sediment at 15,000g. These data are consistent with the morphological studies of Sorokin⁷.