Characterization of phospholipase A from pulmonary secretions of patients with alveolar proteinosis.

Phospholipase A2 (EC 3.1.1.4) from the insoluble pulmonary secretions that accumulate in the lungs of patients with alveolar proteinosis has been purified. The pure enzyme gives a single sharp band upon sodium dodecyl sulfate polyacrylamide gel electrophoresis. Amino acid analysis of the protein shows high content of cystine, aspartic acid, glutamic acid, serine, glycine, leucine and lysine. Only one N-terminal residue, alanine, can be detected. Gel filtration as well as sodium dodecyl sulfate polyacrylamide gel electrophoresis indicate an apparent molecular weight of 75 000 for the enzyme. The enzyme activity has a pH optimum between 7.5 and 8.5 and is stimulated by sodium deoxycholate and CaCl2.