Characterization and Properties of Triacylglycerol Acid Lipase from Fetal and Adult Rat Lung.

The purpose of this research was to investigate intracellular triacylglycerol lipase (TGL) activity from adult and fetal rat lungs. The majority of TGL activity was observed to have two pH optima at 8-9 and 5.0. The alkaline TGL activity was identified as lipoprotein lipase--based on its requirement for serum for activity and inhibition by 0.5 M NaCl. The acidic enzyme activity was identified as acid TGL, and the specific activity in homogenates was similar to lung lipoprotein lipase and acid TGL reported in other tissues. Acid TGL activity in twenty day (gestation) fetal lung homogenates was forty percent of the adult activity, reaching nearly adult levels shortly after birth. Subcellular distribution studies using differential centrifugation, sucrose gradients, and marker enzymes indicated that acid TGL was primarily lysosomal and possibly also lamellar in origin. Acid TGL activity from both fetal and adult lungs was inhibited by 0.5 M NaCl, protamine sulfate, serum, heparin, and 10 mM MgCl(,2), but was unaffected by 10 mM CaCl(,2). The extent of inhibition by MgCl(,2) differed between the lysosomal and microsomal fractions. Analysis of the products of the enzyme reaction, determined by thin-layer chromatography using silica gel impregnated with boric acid, suggested that acid TGL preferentially hydrolyzes the primary acyl bonds of triolein. Twenty day fetal and adult acid TGL activity was inhibited by saturated and unsaturated fatty acids (0.2 mM) and by acidic phospholipids (0.2 mg/ml) while neutral phospholipids had no effect. The similar properties of adult and fetal acid TGL activity suggested that the two enzymes may be structurally similar. Subcellular distribution studies using diolein and monoolein indicated the presence of a separate species of monoacylglycerol hydrolase and a soluble diacylglycerol lipase in adult, but not fetal, lung. The properties of acid TGL suggest it may be involved in regulating the supply of fatty acids and 1,2-diacylglycerol from intracellular triacylglycerol for phospholipid synthesis or other metabolic functions.PhDBiochemistryUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/159709/1/8402249.pd