Isolation and characterization of two hydroxyproline-containing glycoproteins from normal animal lung lavage and lamellar bodies

Intracellular and subcellular oedema and dehydration

Changes in intracellular water content appear to be common abnormalities induced by a wide variety of pathogenic mechanisms. Such changes in cell water produce changes in the water in various subcellular organelles bound by semipermeable membranes. Cell and subcell functions then alter in their turn. In isolated alveolar macrophages (rabbit), intracellular and intramitochondrial oedema reduces mitochondrial O2 utilization. Metabolic control is maintained because lactate production reverses (Pasteur effect). On reconstitution, O2 utilization and lactate production return towards normal, indicating reversibility. Cellular and intramitochondrial dehydration also reduces mitochondrial O2 utilization but metabolic control is lost because lactate production also decreases. Osmotic reconstitution does not reverse the abnormality. Exposure to hypotonic media leads to release of lysosomal enzymes (beta-glucuronidase, EC 3.2.1.31) to the extracellular phase of isolated alveolar macrophages. Some of this release is caused by exocytosis although, at low osmotic concentrations, intralysosomal oedema ultimately ruptures lysosomes, with extensive discharge of enzyme. In turn, lysosomal enzymes may injure more normal cells. Impairment of energy metabolism caused by hypoxia leads to intracellular oedema, because Na+ accumulates in the cells when ATP is no longer available for the sodium pump. Continued studies of the disorders in cell physiology caused by changes in cell and subcell water should provide important new insights into a wide variety of disease states (including pulmonary oedema).

Presence of an 80 kilodalton protein, cross-reacted with monoclonal antibodies to pulmonary surfactant protein A, in the human middle ear

We report the presence of a middle ear protein that has the same epitope as human surfactant protein A. Monoclonal antibodies (PC-6 and PE-10) against human pulmonary surfactant protein A stained faint granules of the mucosal epithelial cell cytoplasm in the orifice of the eustachian tube immunohistochemically. These antibodies also reacted with middle ear effusion of patients with otitis media with effusion by dot immunoassay, and recognized an 80 kd protein by Western blot analysis. These findings indicate that a protein immunoreactive with PC-6 and PE-10 occurs in the mucosal epithelial cells of the middle ear, and is also present in middle ear effusion. It is therefore likely that this 80 kd protein might be secreted from the mucosal epithelial cells to the middle ear cavity.

An HPLC procedure for the analysis of proteins in lung lavage fluid

A high-performance liquid chromatography method has been developed for fractionating the protein components of the lung's extracellular lining fluid, as sampled by bronchoalveolar lavage. With this method, 10 ml (or less) of rat bronchoalveolar lavage fluid (BALF) in phosphate-buffered saline can be quantitatively analyzed rapidly and reproducibly. This volume (25% of the lavage fluid volume from one rat using a standardized lavage technique) is made 0.2% with respect to trifluoroacetic acid (TFA) and pumped through a microBondapak C18 Radial-PAK HPLC column equilibrated with H2O/0.2% TFA. Six fractions are then eluted with a series of acetonitrile gradients and isocratic steps that progress from H2O/0.2% TFA to 65% CH3 CN/0.2% TFA. Following this, 5 additional fractions are eluted with methanol. All 11 fractions are detected by monitoring the column effluents at 206 nm and can be recovered by lyophilization since all the components of the HPLC solvent system are volatile. Nine of the 11 fractions were found to contain protein. Three of the fractions contained proteins common to the blood compartment. The largest fraction of these was albumin, followed by a fraction containing immunoglobulins. Six other protein fractions appeared to be derived from the cells of the lung inasmuch as they were not detected in plasma. Two fractions contained no protein or phospholipids, whereas the most hydrophobic protein fraction did contain phospholipids. A major phospholipid fraction containing no protein eluted early in the chromatogram and was not detectable at 206 nm. This HPLC procedure offers significant utility for identifying and quantifying alterations in several BALF constituents during the development and progression of environmentally induced lung diseases as well as other pulmonary disorders.

Metabolism and turnover of lung surfactant

Despite the grave difficulties that beset researchers who are trying to isolate and characterize the various intracellular and extracellular forms of lung surfactant; despite the serious ambiguities of interpretation of experimental data caused by the multicomponent nature of the surfactant; despite the inaccessibility for diagnostic purposes of this material, which functions deep in the lungs; despite the fact that incisive methods of protein chemistry and molecular biology have only recently been brought to bear on lung surfactant; despite all these problems, our knowledge and understanding of lung surfactant are rapidly increasing. We know now that it is a dynamic system with many parts, and that the reserves of these are normally not large and are recycled. We believe that tight metabolic control must exist to maintain these reserves, and we already have experimental techniques to raise or lower the reserves. Heroic methods of surfactant substitution are now being tested in patients whose deficiency or risk thereof is sufficiently desperate, and the results of these clinical trials, if they are carefully documented with lung function data, will add a new dimension to our knowledge of surfactant dynamics. We may expect in the future that more subtle alterations in surfactant function will become detectable and more sophisticated methods to manipulate the system will be invented. Essential to these will be a deeper understanding of surfactant forms, pathways, kinetics, and controls. Fortunately, research on surfactant structure, metabolism, and turnover intrigues many investigators. They, we may hope, will soon provide the necessary information.

The 35 kd pulmonary surfactant-associated protein is encoded on chromosome 10

The genomic components identified by each of two closely related cDNA clones for the major 35 kilodalton non-serum surfactant-associated proteins (PSP-A) were shown to derive from human chromosome 10 by Southern blot analysis of DNAs from human-rodent somatic cell hybrids. By in situ hybridization to human metaphase chromosomes, the cDNA probes were localized to the region 10q21-q24.

Sialic acid of lung surfactant apoprotein, SP 28-36, is not required for the Ca2+-mediated interactions between surfactant lipids and SP 28-36

We examined whether removal of sialic acid from the lung surfactant apoprotein (SP 28-36) affected certain properties of reassembled surfactant lipid-SP 28-36 complexes. SP 28-36 was treated with neuraminidase and then added to liposomes made from extracted surfactant lipids. We found that in the presence of Ca2+ the asialoprotein was as effective as the native SP 28-36 in binding to surfactant lipids, causing aggregation and promoting rapid surface film formation.

Isolation of protein components from rat lung lamellar bodies

Lamellar bodies isolated from 10% (w/v) rat lung homogenates by discontinuous sucrose gradient centrifugation were shown to contain variable amounts of adhering proteins. These contaminating proteins could be removed by either Sepharose 4B gel filtration or precipitation of the crude preparation at pH 11.5. Both purification methods yielded membrane preparations with a phospholipid-to-protein ratio of 10.0 mumol/mg. Nearly complete separation of lamellar body phospholipid and protein could be achieved upon application of the purified membranes to DEAE-cellulose in the presence of 0.2% (v/v) Triton X-100. Phospholipid analyses showed that 83% of total lipid phosphorus was recovered in phosphatidylcholine. In phosphatidylethanolamine, phosphatidylglycerol, phosphatidylserine and phosphatidylinositol recoveries amounted to 4, 8, 2 and 2%, respectively. Molecular mass determinations of the isolated protein component of lamellar bodies by means of SDS polyacrylamide gel electrophoresis and staining with Coomassie brilliant blue revealed the presence of three protein bands with molecular masses of 64, 33 and 31 kDa. Upon staining with silver a 16 kDa protein was also visible. Sephadex G-100 gel filtration showed only one protein peak corresponding to a molecular mass of 64 kDa when protein was assayed with Coomassie brilliant blue.

Histochemical characterization of an antigen specific for the great alveolar cell in the mouse lung

Previous papers reported on a specific antigenic marker for the great alveolar (type-II) cell of the mouse lung and described its recognition by a specific rabbit anti-adult mouse lung serum. In the present study light- and electron-microscopical immunohistochemistry on fixed mouse lung sections showed the presence of the marker on the alveolar surface. The antigenic determinants recognized by the antibody were further characterized by immunoblotting and immunoprecipitation studies after in vitro translation of mouse lung messenger RNA. Immunoblots of a surfactant-enriched pellet of a bronchoalveolar lavage fraction of mouse lung showed that the antibody reacted with surfactant-associated proteins having apparent molecular weights of about 27,000, 32,000, and 38,000 daltons in SDS gels. Immunoblots of mouse-lung homogenate revealed the presence of 27,000, 30,000, 39,000, and 41,000 daltons proteins, presumably also surfactant-associated proteins. Immunoprecipitation after in vitro translation of mouse-lung mRNA showed specific reactivity only with a 12,000 dalton polypeptide, a component of the cell marker we were unable to relate to surfactant. Our findings indicate that the 12,000 dalton component of the antigenic marker for the great alveolar cell is a polypeptide whose synthesis is a lung-specific process and that the immunoreaction of the larger and surfactant-associated components is due to post-translational modifications.

Induction of glucose 6-phosphatase in cultured hepatoma cells by dexamethasone

The synthetic glucocorticoid, dexamethasone, induced high levels of glucose 6-phosphatase in a line of cultured hepatoma cells (2S FAZA). This conflicts with current theory that glucocorticoids induce a microsomal translocase, specific for glucose 6-phosphate, but not the hydrolase itself. The earlier conclusion was based on experiments with rat livers in vivo in which cortisone was the inducing agent. In the present study, 5 X 10(-6) M dexamethasone induced a tenfold increase in glucose 6-phosphatase activity in "intact" as well as disrupted microsomes using either glucose 6-phosphate or mannose 6-phosphate as substrate. This induction was blocked by cycloheximide (50 micrograms/ml). The broad pH maxima between 5.5 and 7.0 were similar for both "intact" and disrupted microsomes.

Bronchoalveolar lavage proteins

Since the discovery of the extra-cellular lining material of the lung and the possibility harvesting this source by endobronchial lavage this material has been the object of many studies directed to analyze its components, function and possible change in the diseased lung. The best known component of the extra-cellular lining material is the phospholipid and its fatty acid composition. But also on the cellular material much emphasis has been taken with the aim using its cytology as diagnostic parameter. However, very few informations were obtained about the protein material also washed out during the endobronchial lavage. As it was demonstrated by immunological methods the proteins of the extra-cellular lining material consist of serum identical proteins and those being obviously specific for the lung tissue. As found, most serum identical proteins occur in the same amounts as found in the blood serum, and the molecular weight in general range up to 160,000 daltons indicating that there must be a restriction in passage of high molecular weight proteins through the lumen walls of the endothelium. Some proteins, IgG, IgA, do occur in a higher level in the extra-cellular lining material leading to the suggestion that these proteins were synthesized and secreted by the lung tissue itself. The molecular weight of the lung specific proteins range from 16,000-340,000 daltons. Under reducing conditions however, for all species listed, two classes of subunits -36,000 and 12,000 daltons --result, indicating that these proteins might have comparable functions in the different species.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunologically related multimeric forms of 30-40 kDa peptides associated with lung surfactant in various mammalian species

A comparative study of lung surfactant associated proteins was undertaken to determine which mammalian species would best serve as models for investigating alterations of the human lung surfactant system. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of purified surfactants in the presence of dithiothreitol revealed that surfactant invariably contains at least one peptide with molecular weight of 30 000-40 000. In the absence of disulfide reducing agents, the above peptides were in the form of high-molecular-weight proteins (greater than 400 kDa) in primates and cat, whereas in dog, rat and rabbit, the protein was a 72 kDa dimer. The 30-40 kDa peptide subunits were isolated from human, rat and dog surfactants and found to contain four or five residues of hydroxyproline. Antisera to either the human 34 kDa peptide or high-molecular-weight proteins reacted with the high-molecular-weight bands, the 34 kDa subunit and at least six intermediate disulfide-linked forms separated from purified human surfactant by electrophoresis under nonreducing conditions. Following electrophoresis in the presence of dithiothreitol, both antisera detected the 34 kDa peptide as well as other peptides ranging in molecular weight from 23 000 to 160 000. The isolated 34 kDa peptide readily reaggregated into disulfide-linked forms including 68 and 100 kDa complexes which were not reduced by 40 mM dithiothreitol. We conclude that the 34 kDa surfactant-associated peptide forms a complex system of monomeric and multimeric proteins, which varies among the species and could conceivably vary in distribution during lung development or disease.

A comparison of the major surfactant-associated proteins in different species

We examined the major surfactant-associated proteins in a number of species by using two-dimensional gel electrophoresis, protein blotting and immunostaining. All species have a 30,000 to 35,000 mol. wt protein group consisting of multiple isoforms with isoelectric points ranging from pH 4.4 to 5.6. The techniques used in this study have resolved three component subgroups within the 35 K group. A group of proteins at 60,000-65,000 mol. wt has also been consistently identified. We conclude that remarkable similarity exists among the major surfactant-associated proteins from various mammals with regard to isoelectric points, molecular weights and antigenic sites.

An electrophoretic and immunochemical characterization of human surfactant-associated proteins

We have prepared an antiserum against a serum-free extract of alveolar proteinosis lavage that recognizes the same proteins as an antiserum to human surfactant. Using one and two-dimensional gel electrophoresis, protein blotting and immunostaining we have found proteins with Mr of approx. 35 and 60 kDa to be present in every source of human surfactant we have examined. These proteins are immunologically related to those found in the lavage from alveolar proteinosis patients, have the same electrophoretic characteristics and are not found in serum. The 35 kDa protein is a group of at least eight isoforms ranging in relative molecular mass Mr from 32 to 36 kDa with isoelectric points between 4.8 and 5.5. Neuraminidase digestion studies have shown that at least part of this charge heterogeneity may be due to sialic acid residues. The less abundant form, with a Mr of about 60 kDa is also a sialoglycoprotein with similar isoelectric points.

Characterization of two glycoproteins isolated from lung lavage fluid of normal human and from patients with two pulmonary diseases

Two glycoproteins of Mr 62,000 and 36,000 have been isolated and purified from lung lavage of normal human and patients with sarcoidosis and bibasilar fibrosis. The two glycoproteins contained hydroxyproline, high amounts of glycine, and other amino acids in amounts comparable to those present in the same two glycoproteins isolated from lung lavage of patients with alveolar proteinosis. The antibody raised against the glycoprotein of Mr 36,000 isolated from lung lavage material of patients with alveolar proteinosis reacted with both the glycoproteins isolated from normal human as well as from patients with sarcoidosis and bibasilar fibrosis, indicating that these glycoproteins isolated from different sources are structurally related to each other.

Immunohistochemical techniques and their applications in the histopathology of the respiratory system

Subsequent to the first report in the 1940s on incubation of tissue sections with fluorescein-conjugated antibodies for localization of antigens, a great number of modifications were introduced to improve the validity of immunohistochemistry which has become a growingly popular tool. The use of immunoenzymatic techniques eliminates the need for expensive fluorescence microscopy equipment, the lack of permanency of preparations and the lack of electron density required in ultrastructural localization of antigens. Regardless of the technique, it is also important to choose a correct fixation which allows the proper preservation of antigens and morphology and the penetration of antibodies through the entire thickness of the preparation. A variety of immunohistochemical techniques have been applied to study several components of the lung, such as collagen, surface active material, lung specific antigens, and enzymes and the detection of tumor markers, immunoglobulins and infectious agents in the respiratory system which is reviewed. The large surface area and the multiplicity of cell types provided by the respiratory tract epithelium of humans for exposure to microbial as well as toxic substances in the environment make this organ system very vulnerable but a good early indicator of adverse health effects. Immunohistochemistry provides valuable information complementary to the immunochemical and biochemical characterization of this barrier.

The pulmonary extracellular lining

The extracellular lining of the lungs is reviewed. The pulmonary extracellular lining is a complex mixture of phospholipids, proteins and carbohydrates which is absolutely essential for the maintenance of normal pulmonary functions such as gas exchange. Without the lining the lungs would collapse. Alterations in the pulmonary extracellular lining may underlie some disease conditions induced by toxic agents, especially those which interfere with the formation of pulmonary surfactant. The extracellular lining could be used to detect and monitor damage and disease caused by agents toxic to the lungs. The lining contains many hydrolytic enzymes which may act to detoxify certain toxic agents such as those which contain ester groups. The pulmonary extracellular lining could play a significant role mediating the toxic action of inhaled agents as well as the removal of those agents from the lungs.

Synthesis of lung surfactant-associated glycoproteins by A549 cells: description of an in vitro model for human type II cell dysfunction

Immunocytochemical, ultrastructural, and biochemical approaches were used in a series of in vitro and in vivo experiments designed to identify characteristic changes reflecting differentiated type II cell function of A549 cells. Monolayers of A549 cells and A549 clones were maintained in culture for up to 3 weeks. Using an immunoperoxidase (PAP) technique, we demonstrated that variable proportions of A549 cells and of cells in several A549 clones reacted specifically with antibodies to high molecular weight (greater than 400,000) human surfactant-associated glycoproteins (HSAG). The cells of one clone, A549-C12, were consistently negative for HSAG, but their lamellar bodies were similar in appearance and distribution to those found in a PAP-positive clone, A549-C11, as well as in A549 cells. In addition, both C11 and C12 clones displayed time-dependent, divergent differentiation predominantly toward type II epithelium and nonciliated bronchiolar and bronchial cells. Surfactant isolated from either C11 or C12 cells revealed reduced content of disaturated phosphatidylcholine and phosphatidylglycerol when compared to human surfactant; however, a 95,000-dalton peptide immunologically related to HSAG was identified in surfactant from C11 cells but not from the PAP-negative C12 clone. Tumor xenografts produced in athymic (nude) mice following inoculation with cells from C11 and C12 clones exhibited prominent immunoperoxidase staining involving most tumor cells. Cell lines derived from these xenografts (T-11 and T-12) were also enriched in PAP-positive cells. Immunoelectron microscopy indicated that HSAG was localized in the rough endoplasmic reticulum, multivesicular bodies (MVB), intermediate MVB-lamellar forms, and abnormal pleomorphic inclusions. Moreover, two HSAG peptides, both larger than the 34,000-dalton peptide subunit found in normal human surfactant, were present in cells and media from monolayers of the T-11 cell line. We conclude that A549 cells synthesize "defective" HSAG and that the synthesis may be modulated by host factors. The results indicate that appropriate A549 clones can be used effectively as model systems for selected type II cell dysfunctions.

Alveolyn--structure and source: a review

Alveolyn is a unique secretory glycoprotein of 250,000 molecular weight (MW) that is found in distal pulmonary secretions. Several glycoproteins of 130,000 MW, 80,000 MW, 62,000 MW, and 36,000 MW have also been found to be present in the alveolar secretions, and it was found that these glycoproteins were proteolytic fragments of the much larger molecular glycoprotein. It is also a major protein in human amniotic fluid, presumably a product of alveolar secretions. It is also secreted by a clone of pulmonary fetal type II cells. Preliminary results indicate that two of the proteolytic fragments of 62,000 MW and 36,000 MW contain alternate collagenous and noncollagenous domains in the same polypeptide chain. The presence of collagenous domains in these glycoproteins was also confirmed by their susceptibility to digestion with collagenase and the presence of Gly-Pro-Hyp-Gly-type sequence in the peptide chain. Very little is known about the tertiary structure of the protein, except that its fragments bind phospholipids and probably facilitate transfer of the lipid to air-water interfaces.

Characterization of rabbit surfactant-associated proteins

In the present study, the apolipoproteins associated with a purified surfactant fraction isolated from lung lavage of adult rabbits were characterized. Surfactant purity was assessed by the glycerophospholipid composition and by electron microscopic examination. The purified surfactant was delipidated and the apolipoproteins were analyzed by two-dimensional polyacrylamide gel electrophoresis. By use of this technique at least eight proteins or families of proteins were found to be associated with surfactant. Four of these apolipoproteins were families of proteins of 55-70, 29-36, 26-28 and 22-23 kilodaltons (kDa). All of these apolipoprotein families had acidic isoelectric points (pI less than or equal to 5.6), and were specifically bound to a Con A-Sepharose matrix, indicative that these apolipoprotein families are modified by oligosaccharide side-chains. The finding that neuraminidase treatment degraded the 29-36 kDa family is suggestive that this apolipoprotein family contains sialic acid residues. Three major proteins of 66, 43-45 and 35 kDa and a minor protein of 86 kDa were also observed. These proteins had isoelectric points in the more neutral range (pI 6.0-6.5). The 66 kDa protein (pI 6.4) had the same apparent molecular weight and isoelectric point as the major protein of delipidated rabbit serum and as purified rabbit albumin, which suggests that this protein is albumin. These findings are indicative that the apolipoproteins of surfactant are more numerous and complex than previously reported.

Characterization of pepsin-resistant peptides present in a glycoprotein isolated from lung lavage of normal rabbit

A glycoprotein of Mr 36 000 has been isolated from lung lavage of normal rabbit and purified to homogeneity by gel chromatography. Three peptides containing hydroxyproline and nearly 30% glycine have been isolated and purified from pepsin-digested native glycoprotein. Partial NH2-terminal amino acid sequence analysis on one of the peptides indicated the presence of -Gly-Pro-Hyp-Gly- sequence in the peptide chain, suggesting that collagen-like region(s) may be present in this glycoprotein.

Collagen accumulation in the major structures of the rabbit lung during postnatal development

In order to study the accumulation of collagen during postnatal development in the major structures of the lung, trachea, bronchi, pulmonary vasculature, and parenchyma were isolated from the lungs of 1-week, 2-month, and 6-month-old rabbits. The concentrations of DNA, protein, and collagen in parenchyma were similar to those for whole lung. DNA per day weight for all structures declined with age. The DNA concentration of trachea at 6 months was only one-tenth that of parenchyma. Protein per dry weight was constant in parenchyma but dropped by half in trachea and nearly that in bronchi. Collagen per dry weight increased significantly between 1 week and 6 months in all structures. The collagen concentrations in vessels, bronchi, and trachea are similar to each other and three to five times that of parenchyma. The total amount of collagen in bronchi, trachea and parenchyma increased approximately 12-, 50-, and 90-fold, respectively, between 1 week and 6 months of age.

Amniotic fluid secretory immunoglobulin A in normal pregnancy and in pregnancy complicated by rhesus isoimmunization

Amniotic fluid levels of secretory immunoglobulin A (S-IgA) were measured by simple radial immunodiffusion according to the method of Mancini using a monospecific antiserum against the human secretory component. We examined 256 samples from healthy pregnant women and 149 samples from mothers suffering from rhesus isoimmunization. During normal pregnancy amniotic fluid S-IgA increased significantly and showed a loose correlation with the phospholipid levels. This was not observed in pregnancies complicated by rhesus isoimmunization.

Isolation and characterization of lung connective-tissue glycoproteins

1. Glycoproteins of hamster, rat and baboon lung parenchyma were investigated by using [14C]glucosamine incorporation in vitro followed by sequential extraction of the macromolecular components and characterization of the glycoproteins in the extracts. 2. Slices of lung parenchyma maintained in vitro incorporated [U-14C]glucosamine linearly with time into non-diffusible macromolecules for up to 5h. All the macromolecule-associated 14C label was present as [14C]glucosamine. 3. These 14C-labelled macromolecules were extracted from previously delipidated and salt-extracted lung by 5M-guanidinium chloride in the presence of dithiothreitol and proteinase inhibitors before (extract A1) and after (extract A2) hydrolysis of the collagen by collagenase. The [14C]glucosamine-labelled glycoproteins in extracts A1 and A2 contained 55 and 5% respectively of the total [14C]glucosamine incorporated in the lung of all three species studied. 4. The [14C]glucosamine-labelled glycoproteins were analysed by gel-filtration chromatography, sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and isoelectric focusing. The major [14C]glucosamine-labelled glycoproteins of baboon lung parenchyma had apparent mol.wts. of about 400 000, 140 000 and 65 000 with isoelectric points respectively of 4.8, 5.4 and 5.4. The hamster lung glycoproteins with isoelectric points of 4.1 and 5.8 were devoid of hydroxyproline and contained galactose, mannose and N-acetylglucosamine. These experiments indicate that several distinct glycoproteins are synthesized in situ by the cells of pulmonary parenchyma and may well play a role in its structure and function.

[Biosynthesis of pulmonary glycoconjugates. Mechanism of glucosylation of protein and lipid acceptors]

In sheep lung microsomes, we have shown that glucosyl-transferases catalize the transfer of glucose from UDP-glucose into four different acceptors. The glucosylated products obtained are as follows: - a glucosyl-phosphoryl-polyprenol (product A) extractable by chloroform/methanol (2:1 by volume). - a product B extractable by chloroform/methanol/water (10:10:3 by volume). The product B was a mixture of five glycolipids, one of them having a chromatographic behaviour similar to the behaviour of a tetrahexosylceramide (asia-lo-GM1). - a product C insoluble in water and organic solvents which has been demonstrated to be a glycoproteinic compound. The molecular weight of this product C was 160 000 as estimated by gel-filtration. The carbohydrate moiety is composed of small oligosaccharides which are found to be attached by O-glycosidic bond to the protein chain. This linkage is not a collagen-like bond.

Analysis of pulmonary surfactant apoproteins by electrophoresis

Surfactant apoproteins were prepared from detergent-solubilized rat surfactant by immunoaffinity chromatography. SDS-polyacrylamide gel electrophoresis of the apoproteins, without prior chemical reduction, revealed several bands of molecular weights 50 000-78 000, 140 000 and 160 000. Following treatment with dithiothreitol, the apoproteins were resolved into three bands of molecular weights 38 000, 32 000 and 26 000. Further analysis of the apoproteins by two-dimensional polyacrylamide gel electrophoresis showed that each of the proteins of molecular weights 38 000, 32 000 and 26 000 were crosslinked by disulfide bridges and formed homopolymers. Based on periodic acid-Schiff staining, the 38 000 daltghts 38 000, 32 000 and 26 000. Further analysis of the apoproteins by two-dimensional polyacrylamide gel electrophoresis showed that each of the proteins of molecular weights 38 000, 32 000 and 26 000 were crosslinked by disulfide bridges and formed homopolymers. Based on periodic acid-Schiff staining, the 38 000 daltghts 38 000, 32 000 and 26 000. Further analysis of the apoproteins by two-dimensional polyacrylamide gel electrophoresis showed that each of the proteins of molecular weights 38 000, 32 000 and 26 000 were crosslinked by disulfide bridges and formed homopolymers. Based on periodic acid-Schiff staining, the 38 000 dalton protein appeared to be the richest in carbohydrates, followed by the 32 000 and 26 000 dalton proteins. Partial proteolysis of the 38 000 and 32 000 dalton proteins showed similarity in the sizes of peptides generated. Surfactant-associated proteins from human and monkey lungs were also analyzed by polyacrylamide gel electrophoresis. A non-serum glycoprotein of molecular weight 38 000 was found. In different systems of polyacrylamide gel electrophoresis, this protein showed an electrophoretic mobility similar to that of the 38 000 dalton protein of rat surfactant. However, it formed polymers of molecular weight higher than those of polymers found in rat surfactant.

Isolation of a major apolipoprotein of canine and murine pulmonary surfactant. Biochemical and immunochemical characteristics

We studied some of the biochemical and immunochemical properties of a major apolipoprotein in isolated pulmonary surfactant from dog and rat lungs. These apolipoproteins were purified by DEAE-cellulose chromatography in buffers containing Triton X-100. Purity of the apolipoproteins was assessed by both fused rocket and crossed immunoelectrophoreses. In addition, the apolipoproteins showed one band with an apparent molecular weight of 72 000-73 000 on SDS-polyacrylamide gel electrophoresis. These proteins are composed of two polypeptide chains of 36 000 daltons. When subjected to isoelectric focusing, the major component of the apolipoprotein had an isoelectric point of about 4.4, with very minor components near 4.6. Even though the apolipoproteins of both species had very similar amino acid compositions, including a relatively high glycine content, no immunologic cross-reactivity was observed. Rocket immunoelectrophoretic analysis of several preparations of dog and rat surfactant using the respective purified apolipoproteins as standards indicated that the apolipoprotein constituted 56.9% +/- 4.6. (S.D., n = 3) and 42.1% +/- 2.1 (S.D., n = 2) of the total protein in dog and rat surfactant, respectively.

Phospholipids of the lung in normal, toxic, and diseased states

The highly pulmonary concentration of 1,2-dipalmitoyl-sn-glycerol-3-phosphorylcholine (dipalmitoyllecithin) and its implication as an important component of lung surfactant have promoted investigation of phospholipid metabolism in the lung. This review will set the contents including recent informations for better understanding of phospholipid metabolism of the lung in normal state (physiological significances of lung phospholipids, characteristics of phospholipids in lung tissue and alveolar washing, biosynthetic pathways of dipalmitoyllecithin, etc.) as well as in toxic states (pulmonary oxygen toxicity, etc.) and in diseased states (idiopathic respiratory distress syndrome, pulmonary alveolar proteinosis, etc.) Since our main concern has been to clarify the most important route for supplying dipalmitoyllecithin, this review will be focused upon the various biosynthetic pathways leading to the formation of different molecular species of lecithin and their potential significance in the normal, toxic, and diseased lungs.

Isolation, characterization and localization of a 45 000 molecular weight, soluble glycoprotein from the lung in pulmonary alveolar proteinosis

A carbohydrate-rich, water-soluble glycoprotein has been isolated in pure form from delipidated lung lavage fluid from a patient with pulmonary alveolar proteinosis, in a three-step procedure involving ion-exchange and gel filtration chromatography. The molecular weight of the glycoprotein was determined to be 45 900 by sedimentation equilibrium analysis in the analytical ultracentrifuge and 45 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate, indicating a single polypeptide chain. Nearly half of the mass of the glycoprotein is comprised of carbohydrate that is contributed by 24 residues sialic acid, 23 residues N-acetylglucosamine, 6 residues N-acetylgalactosamine, 19 residues galactose, 4 residues mannose, 1 residue fucose and 1 residue glucose per mol. Unlike a number of collagen-related glycoproteins that have been isolated by others from insoluble lung contents in pulmonary proteinosis, the water-soluble glycoprotein described in the present report does not contain hydroxyproline or hydroxylysine and contains less than 10% of its amino acid residues as glycine. Using rabbit antibodies directed against our purest preparation of material and an immunoperoxidase staining procedure, the 45 000 molecular weight glycoprotein was localized to the thin film of fluid lining the surfaces of alveoli in normal human lungs.

Characterization of collagenous and non-collagenous peptides of a glycoprotein isolated from alveoli of patients with alveolar proteinosis

A glycoprotein of Mr 62 000 was isolated from lung lavage material of patients with alveolar proteinosis. The glycoprotein was found to contain (per molecule) 72 residues of glycine, 5 residues of hydroxyproline, 3 molecules of sialic acid, 4.9 molecules of mannose, 4.0 molecules of galactose, 0.9 molecule of fucose and 7.0 molecules of N-acetylglucosamine. Limited pepsin digestion of the glycoprotein resulted in six peptides, three of which contained hydroxyproline and nearly 30% glycine, and two of which contained all the carbohydrate present in the glycoprotein of Mr 62 000. The three peptides containing hydroxyproline and with high content of glycine contained a repeating -Gly-X-Y-sequence in the peptide chain. Partial amino acid-sequence analyses on the peptides derived from the digestion of the alveolar glycoprotein with various proteolytic enzymes indicate that this glycoprotein is characterized by the presence of alternating collagenous and non-collagenous regions in the same polypeptide chain.

Effects of inhibiting protein synthesis on the secretion of surfactant by type II cells in primary culture

Pulmonary surfactant is isolated from the alveolar lumen as a complex of lipid and protein (King, R.J., Martin, H., Mitts, D. and Holmstrom, F.M. (1977) J. Appl. Physiol. 42, 483-491). We wished to determine whether the secretion of this complex was dependent upon cellular activities associated with the synthesis of protein, and whether the pre-formed lipids of surfactant would be released from the cell even though the synthesis of newly-formed protein was inhibited. Alveolar epithelial Type II cells were isolated from adult rat lung and grown to confluency in primary culture. The synthesis and secretion of the apolipoprotein of surfactant and its principal lipid, dipalmitoyl phosphatidyl-choline, were followed by isotopic precursor techniques. The synthesis of the apolipoprotein was reduced to 14% of control by 1 . 10(-4) M cycloheximide and to 2.5% of control by 4 . 10(-4) M cycloheximide. These concentrations of cycloheximide, however, had no effect on the rate of synthesis or release of DPPC. The secretion of the apolipoprotein which had been synthesized before the addition of 1 . 10(-4) M cycloheximide was not inhibited by this compound. Cells maintained at 5 degrees C neither synthesized nor released surfactant. We conclude, therefore, that the synthesis of cellular protein is not required for the secretion of surfactant, but that the continuous generation of metabolic energy may be essential. These results, together with those of previous kinetic studies (see above references), suggest that the lipid and protein constituents of surfactant may be contained within lamellar bodies prior to their release into the extracellular environment.

Structural studies on a collagen-like glycoprotein isolated from lung lavage of normal animal

A major glycoprotein of Mr = 36 000 has been isolated from lung lavage of normal rabbit and purified to homogeneity by gel chromatography. The glycoprotein was found to contain 4 residues hydroxyproline, 50 residues glycine, 3 residues methionine, 2.6 mol sialic acid, 4.0 mol galactose, 5.0 mol mannose, 0.9 mol fucose and 7.0 mol glucosamine. Cyanogen bromide treatment of the glycoprotein resulted in four peptides with molecular weights of 18 000, 12 000, 5000 and 1000, three of the peptides containing hydroxyproline and two of the peptides containing carbohydrates. Partial NH2-terminal amino acid sequence analysis on one of the cyanogen bromide peptides (Mr = 18 000) indicated the presence of -Gly-Pro-Hyp-Gly- sequence in the peptide chain, suggesting that collagen-like region(s) may be present in this glycoprotein.

Characterization of the collagen- and non-collagen-like regions present in a glycoprotein isolated from alveoli of patients with alveolar proteinosis

A major glycoprotein of Mr 36 000 has been isolated from the lung lavage of patients with alveolar proteinosis and found to contain five residues of hydroxyproline, 50 residues of glycine, 2.6 mol of sialic acid, 4.8 mol of mannose, 4.1 mol of galactose, 0.9 mol of fucose, 7.0 mol of N-acetylglucosamine. Limited pepsin digestion of this glycoprotein resulted in six peptides, three of which contained hydroxyproline and nearly 30% glycine and two of which contained all the carbohydrate present in the native glycoprotein. All three peptides containing hydroxyproline and high content of glycine were found to contain -Gly-x-y-Gly- type sequences. Partial amino acid sequence analyses indicate that this glycoprotein is composed of alternating short collagen- and non-collagen-like peptide sequences.

Secretory IgA is a component of rabbit lung surfactant

Secretory IgA is a major protein component of rabbit lung surfactant purified by NaBr density gradient centrifugation from endobronchial lavage and minced lung tissue. Secretory IgA was found in both surfactant and non-surfactant fractions obtained from endobronchial lung washings. By contrast in minced-lung washings, which are not contaminated with proteins from the upper respiratory tree, secretory IgA is prominent only in the surfactant fraction. These findings indicate that in rabbit lung secretory IgA is present in the alveoli and is intimately associated with the surfactant system.

Hydrophobic proteins of lamellated osmiophilic bodies isolated from pig lung

1. In addition to proteins that are insoluble in organic solvents, lamellated bodies isolated from pig lung and surfactant prepared from bronchopulmonary lavage fluid contain another group of proteins that are extracted together with lipid into the organic phase. 2. These hydrophobic proteins constitute about 40% of the total protein of lamellated bodies and about 13% of the total protein of surfactant isolated from lavage fluid, whereas less than 1% of the total protein of pig lung microsomal fraction and mitochondria is extracted by organic solvents. 3. The hydrophobic proteins of lamellated bodies were separated into four fractions and freed from phospholipid by chromatographic procedures. Their apparent molecular weights vary between 11 500 and 16 500, they contain 72--79% of hydrophobic residues and 16--22% of sulphur-containing amino-acids, and leucine is the major N-terminal amino acid in each case.

Physicochemical properties of dipalmitoyl phosphatidylcholine after interaction with an apolipoprotein of pulmonary surfactant

We studied the interaction between an apolipoprotein of pulmonary surfactant and the principal lipid found in this material, dipalmitoyl phosphatidylcholine. The apolipoprotein was extracted from canine surfactant and purified to greater than 90% homogeneity. The apolipoprotein was mixed for 16 h at room temperature with dipalmitoyl phosphatidylcholine dispersed in a buffer containing 0.1 M NaCl and 3mM CaCl2. Unbound lipid, unbound protein, and recombinants of lipid and protein were separated by density gradient centrifugation. 71% of the apolipoprotein was found associated with dipalmitoyl phosphatidylcholine. In comparable experiments using bovine plasma albumin about 13% of the albumin was recovered with the lipid. The physicochemical state of the lipid in the apolipoprotein-lipid complex was modified after binding of the protein. A distinct phase transition at 42 degrees C could no longer be detected, and the rate of adsorption to an air-liquid interface of the apolipoprotein-lipid complex was greater than that of the lipid alone. Surface tension vs. surface area isotherms of the dipalmitoyl phosphatidylcholine-apolipoprotein materials, however, were similar to those exhibited by pure dipalmitoyl phosphatidylcholine. The results suggest a physiological role for this apolipoprotein. It may bind to dipalmitoyl phosphatidylcholine under conditions expected in vivo, and may modify the physical properties of the aggregated dipalmitoyl phosphatidylcholine to form domains of lipid in a liquid-crystalline array. The complex dipalmitoyl phosphatidylcholine and apolipoprotein would have the physical properties necessary for its physiological function, allowing it to absorb to the alveolar interface and reduce its surface tension to less than 10 dynes/cm. Dipalmitoyl phosphatidylcholine, by itself, is in a gel-crystalline array below its phase transition temperature (42 degrees C) and would be incapable of effecting these actions.