CHARACTERIZATION OF A DIMERIC CANINE FORM OF SURFACTANT PROTEIN C(SP-C)

Canine pulmonary surfactant protein C (SP-C) is a small hydrophobic pe ptide which has one palmitoylated cysteine residue. SP-C enhances the insertion of phospholipids into a monolayer. Two forms of canine SP-C were isolated using Sephadex LH-60 chromatography. It was found that c anine SP-C exists in a palmitoylated monomeric form of 3.5 kDa, and a non-acylated dimeric form of 7 kDa. Circular dichroism showed that bot h forms of SP-C exhibit similar secondary structures at the air/water interface. Both forms of SP-C were able to induce the insertion of pho spholipids into a monolayer as measured with the Wilhelmy plate techni que. In contrast to the palmitoylated monomeric form of SP-C, the non- acylated dimeric form of SP-C does not require calcium ions to insert phospholipids into a monolayer without the negatively charged phosphat idylglycerol. It is concluded that two forms of canine SP-C exist, but the physiological significance of these different forms remains to be established.