1. Isolated rat lungs were perfused with a variety of radioactive precursors to label the
phosphatidylcholines of the microsomal and lamellar body fractions. These endogenously
labelled phosphatidylcholines were used as substrates in experiments to identify and
characterize phospholipase A activity in lung subcellular fractions. 2. 2. The microsomal
fraction was found to contain a phospholipase A specific for the 2-position of endogenous
phosphatidylcholines. The enzyme operated optimally at pH 8.5 and required 10 mM Ca 2+ …