Fig. 3
Calculated experimental molecular weight values for the SP-A peaks observed by gel filtration. The samples analyzed were fractions from gel filtration of BAL from a PAP patient. Pooled fractions 8–11, 11–15, 15–19, and 19+ were analyzed by sucrose density gradient centrifugation, fractions were analyzed by ELISA, and the sedimentation coefficient (S20,w) of the major SP-A peak was calculated as in Materials and Methods. Values for the molecular weights of each gel filtration peak were calculated from the sedimentation coefficient and Stoke’s radius of each sample. The fractions corresponding to the oligomeric forms shown in the figure were fractions 8–11 for hexamers; 11–15 for tetramers; 15–19 for dimers; and 19+ for polypeptides. The expected sizes of SP-A oligomers are: hexamers, 540 kD; tetramers, 360 kD; dimers, 180 kD, and polypeptides, 30 kD. This is based on the molecular weight of a single polypeptide being approximately 24 kD with up to 6 kD of oligosaccharides.