The Anionic Phospholipids of Bovine Pulmonary Surfactant

Abstract

The only known compositional change in the phospholipids (PL) of pulmonary surfactant in response to a physiologic stimulus occurs around the time of birth. In most species, the predominant anionic PL changes from phosphatidylinositol (PtdIns) to phosphatidylglycerol (PtdGro). Because prior studies have shown that the change in the headgroup itself is functionally insignificant, we tested the hypothesis that the PtdIns and PtdGro contain different diacyl pairs. Experiments used electrospray‐ionization mass spectrometry to determine the molecular species in PtdIns, PtdGro, and phosphatidylcholine (PtdCho) in surfactant from newborn calves and cows. The profiles for the two anionic PL were distinct. The PtdIns contained long, unsaturated fatty acid chains and no disaturated species. The PtdGro more closely resembled the profile from PtdCho. For each headgroup, the molecular species for calf and cow were similar. The differences between the two anionic PL indicate that the switch from PtdIns to PtdGro during maturation involves more than simple substitution of the headgroup, and suggest that the functional significance of the shift may reflect the different pool of diacyl pairs.

Location of the Hydrophobic Surfactant Proteins, SP-B and SP-C, in Fluid-Phase Bilayers

“…The ratio of N&PL and CLSE was expressed as the mole fraction between 0 and 1.0 of phospholipid contributed by CLSE ( X CLSE ). Weight ratios were calculated by using an average molecular weight for the lipids in CLSE of 736 Da …”

“…Weight ratios were calculated by using an average molecular weight for the lipids in CLSE of 736 Da. 27 The mixtures were plated onto silicon wafers (15 × 1.5 × 30 mm 3 ) via the rock-and-roll method, 28 in which rocking the silicon wafer continuously during solvent evaporation produces stacks of ∼1800 well-aligned bilayers. Once immobile, further solvent was evacuated for at least 2 h. The sample was trimmed to a central strip 5 mm wide and parallel to the long edge of the wafer.…”

Suppression of Lα/Lβ Phase Coexistence in the Lipids of Pulmonary Surfactant

“…Concentrations of the proteins and phospholipids were determined by colorimetric assays (30,31), using bovine serum albumin as the standard protein. The content of the proteins (32), their physical constants (Table 1), and the composition of the lipids (16,27,34,35) in CLSE are all known. SP-B and SP-C represent $1.5% (w/w) ($500:1 lipid/ protein molar ratio) of the complete mixture (32).…”

“…During progressive hydration, multilamellar vesicles of zwitterionic phospholipids swell to a finite, maximal D-spacing, which then remains constant with further hydration. Samples containing anionic phospholipids, such as N&PL and CLSE (16,27,35), can swell without limit because of electrostatic repulsion, which leads to the absence of diffraction (39,40). The lack of well-defined values of D-spacing for our samples when dispersed in excess water complicated efforts to show that our films achieved full hydration.…”

A recipe for a good clinical pulmonary surfactant

“…The phospholipid phosphatidylglycerol (PG) is a typical component of the plasma membrane of bacteria such as Escherichia coli , and of the membranes of plant cells, but very unusual in animal cell membranes. However, PG, and also phosphatidylinositol (PI), are the most abundant anionic phospholipid species in lung surfactant [ 42 , 43 , 55 ]. Typically, PI antecedes metabolically the appearance of PG, as it is a precursor in the pathway to its biosynthesis, but PI also constitutes a significant fraction of mature surfactant and in some animal species PI is even more abundant than PG [ 55 ].…”