Surfactant-associated 15- and 35-kDa proteins are concentrated in different organelles in rat lung tissue.
We have used isopycnic gradient ultracentrifugation to isolate a total lamellar body fraction (total-lb) from rat lung and then further subfractionated this using differential centrifugation to obtain two distinct subpopulations of organelles. When the total-lb was diluted to 0.25 M with sucrose and centrifuged at 8000 X for 30 min we obtained a fraction (lbA) that contained primarily intact classic-appearing lb. When the supernatant was then centrifuged at 80,000 X g for 60 min we obtained a vesicular fraction (lbB). Whereas both fractions had an identical phospholipid composition, their enzyme profiles differed markedly. The lbA had a higher level of beta-glycerophosphatase, while lbB had more 5'-nucleotidase. Moreover, lbB had a phospholipid:protein ratio of 9.2 while lbA had one of 6.3. An examination of the specific activity-time curves revealed that lbA had a curve that was broader and reached a peak earlier than lbB, but the downslopes of both curves were identical; they did not bear a classic precursor-product relationship to one another. The two fractions differed very significantly in their protein profiles. Whereas lbA contained a large amount of a 15-kDa protein with very small amounts of 35-, 37-, 38-, 45-, and 60-kDa proteins, lbB contained predominantly a 35-kDa protein with smaller amounts of 15-, 23-, 26-, 37-, 38-, 45-, and 60-kDa proteins. We suggest that lbB is surfactant taken back up into the alveolar type II cell, or a second release form of tissue surfactant, or a mixture of the two.
Power
J H
JH
Department of Physiology, School of Medicine, Flinders University of South Australia, Adelaide.
Barr
H A
HA
Nicholas
T E
TE
D000818:Animals; D002458:Cell Fractionation; D008168:Lung / Q000648:ultrastructure*; D008970:Molecular Weight; D009940:Organoids / Q000032:analysis*; D011506:Proteins / Q000032:analysis; D011510:Proteolipids / Q000032:analysis*; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants / Q000032:analysis* / Q000096:biosynthesis; D051381:Rats; D011919:Rats, Inbred Strains
D011506:Proteins; D011510:Proteolipids; D037661:Pulmonary Surfactant-Associated Proteins; D011663:Pulmonary Surfactants