Lung phosphatidate phosphatase: activity during altered physiologic states.

Phosphatidic acid phosphatase (PAPase) which catalyzes the conversion of phosphatidic acid to 1,2-diacyl-sn-glycerol was studied in fetal, neonatal, and adult rat lung microsomal fractions from whole lung under normal and altered physiological states. The maximal activity was obtained at pH 7.0 with 1.0 mM phosphatidic acid as the substrate. Twenty-one-day-old fetal rat lung averaged 20.3 +/- 0.6 SE nmol/min/mg microsomal protein compared to 9.9 +/- l.0 nmol/min/mg in liver. Following birth there was a dramatic 53% increase in the PAPase activity. Twenty-one-day-old fetal rat lungs from diabetic mothers (streptozotocin-induced) and from mothers fasted the last four days of gestation did not show altered PAPase activity. Premature breathing for 3-6 hr on day 21 of gestation also did not affect the PAPase activity. These data demonstrate that the microsomal PAPase activity (l) increases dramatically only after birth (2) is not responsive to altered physiologic state (maternal diabetes, maternal fasting, and premature breathing) and (3) may not be an important regulatory enzyme in lung surfactant phospholipid production.