Enzymes of phospholipid metabolism in airway secretions of patients with asthma, cystic fibrosis, and alveolar proteinosis.

Phospholipase A2, lysolecithinase, and lysolecithin-lysolecithin acyltransferase are present in the airway secretions 
of patients with asthma, cystic fibrosis (CF), and alveolar proteinosis. Assays 
of these enzymes under the same conditions in extracts of human 
polymorphonuclear leukocytes, alveolar macrophages, and pig tracheal mucosa indicated that these 
extracellular airway enzymes were probably not derived from these cell types. 
Although the above three enzymes were present in secretions of all 
patients with these three diseases, large amounts of palmitoyl lysolecithin, free 
fatty acids, and dipalmitoyl lecithin were found only in patients having 
alveolar proteinosis and asthma. The amount of free fatty acids in 
these secretions was sufficient to inhibit both the lysolecithinase and the 
lysolecithin-lysolecithin acyltransferase, but not the phospholipase A2. These findings suggest that 
the large amount of dipalmitoyl lecithin, free fatty acids, and lysolecithin 
found in these secretions results from extracellular remodelling by these enzymes. 
Because the phospholipase A2 was present in large amounts, it was 
possible after delipidation to purify it to homogeneity. It is a 
stable enzyme with an apparent molecular weight of 75,000 as estimated 
by SDS-mercaptoethanol gel electrophoresis. 