title: A study on the topological distribution of phospholipids in microsomal membranes of chick brain using phospholipase C and trinitrobenzenesulfonic acid.
abstract: The transbilayer distribution of phospholipids in chicken brain microsomal membranes has been investigated using trinitrobenzenesulfonic acid and phospholipase C from Clostridium welchii. The exposure of intact microsomes to trinitrobenzenesulfonic acid showed that the labelling of aminophospholipids followed biphasic kinetics, indicating that these membranes contain a fast- and a slow-reacting pool of aminophospholipids. Use of microsomes radioiodinated on their surface led to the conclusion that the fast-reacting pool may be located on the outer leaflet of the microsomal vesicles. It contains about 35% of the phosphatidylethanolamine, 29% of the ethanolamine plasmalogens and 18% of the phosphatidylserine. The treatment of intact microsomes with the phospholipase C Cl. welchii produced the hydrolysis of 50% of the phospholipids without any loss of their permeability properties, indicating that they are not permeable to the hydrolase. Phospholipids extracted from the microsomes were hydrolyzed rapidly by the phospholipase C with the exception of phosphatidylserine and phosphatidylinositol. In intact microsomes about 90% of phosphatidylcholine, 32% of ethanolamine phospholipids and 60% of sphingomyelin were accessible to the phospholipase. These results suggest that the phospholipids have an asymmetric distribution in chicken brain microsomes, the external leaflet containing about 75% of the choline phospholipids and 25% of the aminophospholipids, whereas an opposite distribution is observed in the inner leaflet.
mesh_terms: D000818:Animals; D001921:Brain / Q000648:ultrastructure*; D002645:Chickens; D007425:Intracellular Membranes / Q000378:metabolism*; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism*; D009578:Nitrobenzenes / Q000494:pharmacology*; D010740:Phospholipases / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D013997:Time Factors; D014018:Tissue Distribution; D014302:Trinitrobenzenesulfonic Acid / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*
chemical_list: D009578:Nitrobenzenes; D010743:Phospholipids; D014302:Trinitrobenzenesulfonic Acid; D010740:Phospholipases; D010738:Type C Phospholipases