Lysophospholipase--transacylase from rat lung: isolation and partial purification.

Incubation of rat lung supernatant with 1-[1(-14)C] palmitoyl-sn-glycero-3-phosphocholine in the absence of any cofactors resulted in the release of radioactive fatty acid and the formation of phosphatidylcholine. The production of fatty acids (lysophospholipase activity) exceeded phosphatidylcholine formation (transacylase activity) about thereefold, although the relative extent of phosphatidylcholine formation was considerably greater than previously reported by Abe et al. (Biochim. Biophys. Acta, 369: 361-370, 1974). In agreement with these authors, evidence is presented suggesting that a single enzyme is responsible for both catalytic activities. The enzyme, provisionally denoted lysophospholipase-transacylase, was found primarily in the soluble fraction of rat lung and was purified approximately 250-fold. The enzyme had an estimated mol wt of 50,000. The ratio of lysophospholipase to transacylase activity in the purified enzyme could be varied depending upon the concentration and character of the lysophosphatidylcholine and the ration of substrate to products. The degree of esterification of 1-acyl lysophosphatidylcholine was altered with mixtures of different molecular species of substrate, indicating acyl chain selectivity in the transfer process. This enzyme was capable of synthesizing disaturated phosphatidylcholine, an important component of the pulmonary surfactant. Three lysophospholipases purified from other sources did not possess this transacylase activity.