Metabolic fate of the apoproteins of pulmonary surfactant

In summary, we now have evidence that a nonserum protein with a nominal molecular weight of 35,000 daltons is secreted into the alveolar lumen with the same time course as that of the lipids in surfactant. The kinetics of its clearance are different from those describing the clearance of the lipids, and it is possible that it is catabolized to smaller peptides before its removal from the alveoli. Alveolar macrophages may participate in the clearance of surfactant, but the quantitative importance of this pathway is unknown. Still to be absolutely confirmed is the specificity of this protein to pulmonary surfactant. The availability of relatively pure populations of type II alveolar cells may accelerate progress in the endeavor.