Abstract
Studies on the pulmonary surface-active lipoprotein complex were carried out in order to establish. primarily, its biochemical characteristics.
By means of differential centrifugation in salt gradients, surface-active lipoprotein complex was obtained from fresh human, guinea pig and bovine lung tissue.
The three species of SA-lipoproteins proved remarkably similar in chemical composition, in accordanee with their homologous functions.
After removal of lipids with an extraction technique developed by the author, the peptide of the cow lung SA-lipoprotein was subjected to an exhaustive characterization study. total nitrogen, lipids. 15.73 per cent 5.85 per cent carbohydrate, and no detectable The delipidized peptide contained approximately The sialic acid content of the delipidized peptide did not change after precipitation with trichloroacetic acid and perchlorie acid reagents, which suggests that earbohydrates form an integral part of the SA-peptide molecule and do not result from the presence of impurities.
Amino acid analysis of SA-peptide revealed the presence of all the amino acids normally found in protein hydrolysates. In addition, two unusual amino acid constituents were found, allo-isoleucine and hydroxylysine. These relatively uncommon amino acid constituents ,may serve as useful markers for identifying the peptide moiety of SA-lipoprotein in future studies. position of SA-lipoprotein differs qualitatively and The amino acid com quantitatively from that of other well-known lipoproteins and of serum albumin as well.
A low level of alkaline phosphatase activity was detected in SA-lipoprotein. No sueh enzymatie activity was found in the SA-peptide moiety. This biological activity may be charaeteristic of the SA-lipoprotein but eould also resutt from contamination with discrete lung alkaline phosphatase enzymes.