Myocardial phospholipase A of microsomal and mitochondrial fractions

Phospholipase A and lysophospholipase activity of the epidermis

Phospholipase A and lysophospholipase activities have been demonstrated in cow snout epidermis. The phospholipase A activity was dependent on Ca2+ ions and the pH for optimum activity was between 6-1 and 7-4.

Metabolic fate of fatty acids in the carnitine cycle of brown adipose tissue mitochondria

Freshly isolated mitochondria from brown adipose tissue are uncoupled with respect to oxidative phosphorylation. When these mitochondria oxidize[U-minus 14-C] palmitic acid in the presence of malate the label is found in three major fractions. Polar lipids, rich in acyl carnitines, remain in the mitochondrial pellet. A large fraction, rich in tricarboxylic acid cycle intermediates, is exported to the suspending medium, as is a third, smaller fraction containing ketone bodies and beta-hydroxy-beta-methylglutaric acid. Prevention of oxygen uptake by addition of rotenone or antimycin prevents accumulation of cycle intermediates, increases formation of acyl carnitiness and increases beta-hydroxybutyrate relative to acetoacetate. Rotenone and antimycin do not prevent formation of labeled phosphatidylcholine. Partial suppression of oxygen uptake by benzene-1,2,3-tricarboxylic acid, amytal or malonate leads to results between these extremes. Addition of lysophosphatidylcholine had minimal effects on export of cycle intermediates, but increased formation of ketone bodies and particularly of acyl carnitines. The significance of lysophosphatidylcholine as an endogenous modifier of mitochondrial metabolism is discussed.

Preparation and characterization of mouse intestinal phospholipase

Phospholipase has been prepared in a stable, partially purified form from the small intestine of mice infected with the tapewormHymenolepis nana. The enzyme(s) attacks diacylphosphatides with liberation of free fatty acids and a corresponding decrease in phospholipid phosphorus, without accumulation of lysophosphatides. The reactivity with various substrates is strongly influenced by their physical state, the presence of other lipids, proteins or detergents. The phospholipids of some biomembranes (mitochondria, microsomes, red cell ghosts) are readily hydrolyzed under customary reaction conditions. The ensuing biochemical, morphological and functional alterations have been documented. In contrast, the diacylphospholipids of the cell membrane (intact erythrocytes,Pseudomonas aerunginosa) are not accessible to phospholipase action unless some alteration of the integrity of the cell is induced by physical or chemical means (hemolysis, polymyxin). The enzyme is proposed as a tool for the investigation of biomembranes and as a model for the study of phospholipase activity.