Fatty acid chain-shortening activity in the pulmonary type II cell.

Type II cells obtained from fetal rabbit lung tissue in culture were incubated with [14C]palmitic and [14C]stearic acids labeled at either the carboxyl or the terminal methyl groups. Significant chain shortening of [18-14C]stearic acid to radiolabeled palmitic acid was observed, with little chain shortening of palmitic acid to myristic acid. Incorporation of 14C into palmitic acid by beta-oxidation followed by de novo fatty acid biosynthesis was not detectable under the same experimental conditions. The palmitic acid supplied by chain shortening was preferentially incorporated into phosphatidylcholine instead of other lipids. Fatty acid chain-shortening activity in the type II cell appears to be capable of increasing the amount and relative proportion of palmitic acid available for phosphatidylcholine biosynthesis.