The action of lung lysosomal phospholipases on dipalmitoyl phosphatidylcholine and its significance for the synthesis of pulmonary surfactant.
Subcellular fractions were prepared from rabbit lung and characterized by marker enzyme assays. Phospholipases A of lysosomal type (activity at pH 4.0 in the absence of Ca2+) show a peak of specific activity in fraction P3 (13000 x g; 20 min; pellet). About 70% of the phospholipase A activity of P3 can be obtained in a soluble extract. The rates of hydrolysis of dipalmitoyl (saturated) and unsaturated phosphatidylcholine molecules, presented to enzyme preparations in liposomes of varying composition, are shown in Tables 3 to 5. Although the rate of unsaturated molecules is unaffected by liposome composition, saturated molecules are hydrolyzed significantly faster in 5 mol % dipalmitoyl phosphatidylcholine liposomes than in 95 mol %. With enzyme preparation I (60% A1: 40% A2) the increase was 6-fold (P less than 0.01). Preparations I and II hydrolyzed both kinds of molecules at similar rates in 50 mol % dipalmitoyl phosphatidylcholine liposomes, but preparation III, with a higher proportion of A2 (80%), gave a notably lower rate of hydrolysis of saturated molecules. Phosphatidylglycerol (10 mol %) also decreased the rate of hydrolysis of saturated molecules. These results are discussed in relation to fluidity of the liposomes and to the functions of the lysosomal-type phospholipases A of the lamellar inclusion bodies of the lung.
D000818:Animals; D006868:Hydrolysis; D008168:Lung / Q000201:enzymology*; D008247:Lysosomes / Q000201:enzymology; D010713:Phosphatidylcholines / Q000378:metabolism*; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000096:biosynthesis*; D011817:Rabbits
D010713:Phosphatidylcholines; D011663:Pulmonary Surfactants; D010740:Phospholipases; D010741:Phospholipases A