Exchange of phospholipids between brain membranes in vitro

Abstract

1. When unlabelled mitochondria from guinea-pig brain were incubated with a (32)P-labelled microsomal fraction from brain there was a transfer of phospholipid to the mitochondria, which could not be accounted for by an aggregation of microsomes and mitochondria or an exchange with microsomes contaminating the mitochondria. Under similar circumstances there was a transfer of phospholipid from (32)P-labelled mitochondria to microsomes, indicating that the process was one of exchange. 2. The transfer from microsomes was greatly stimulated by a non-dialysable heat-labile macromolecular component in the brain supernatant fraction but not by the concentration of the particulate fractions. 3. Phospholipid-exchange processes occurred most readily between pH7 and 7.5 and were inhibited by the presence of myelin and on the addition of lysophosphatidylcholine. 4. The rates of transfer of individual phospholipids from brain microsomes to mitochondria were similar. 5. (32)P-labelled microsomes could slowly donate phospholipid to the isolated synaptosomal (nerve-ending) fraction but the phospholipids of the myelin fraction did not exchange. 6. Subfractionation of the synaptosomal fraction after [(32)P]phospholipid transfer showed that the mitochondria were most actively labelled during the incubation. All of the isolated individual synaptosomal membranes were capable of acquiring phospholipid on incubation with a (32)P-labelled brain supernatant fraction although a greater percentage was again exchanged by the mitochondrial fraction.

Transfer of phospholipids between membrane

“…Miller and Dawson [79] observed a transfer of 32p-labelled phospholipids from 32p-labelled guinea pig brain microsomes to unlabelled brain mitochondria in the presence of a brain supernatant. In this study it was shown that the extent of exchange varied with the subcellular membrane particles present in the medium.…”

“…SOME PROPERTIES OF THE pH 5.1 SUPERNATANT FRACTION Phospholipid-exchange activity has been demonstrated in the cell supernatant of a wide variety of tissues such as rat [55,56,66], guinea pig [41] and beef liver [83]; rat [85 ], guinea pig [79 ] and beef brain [86]; rat [85 ] and beef heart [87 ]; rat kidney [85]; and pig thyroid [80]. Exchange activity was not detected in plasma of rat [41] and squirrel monkey [84].…”

Phosphatidylinositol metabolism in cells receiving extracellular stimulation

“…This conclusion is supported by the isolation, from a liver soluble fraction which catalyses exchange of several lipids, of a protein which catalyses exchange only of phosphatidylcholine [83] . In such experiments with isolated subcellular fractions, the exchange of phosphatidylinositol was rapid in comparison to that of other phospholipids [81] and phosphatidic acid exchange was comparable to that of other lipids [84].…”

The incorporation of radioactive fatty acids and of radioactive derivatives of glucose into the phospholipids of subsynaptosomal fractions of cerebral cortex

“…By using liver (Wirtz & Zilversmit, 1968;McMurray &Dawson, 1969)and brain (Miller &Dawson, 1972b) subfractions, a transfer of phospholipids between microsomal and mitochondrial fractions and also between a brain supernatant fraction and subsynaptosomal fractions (Miller & Dawson, 1972b) has been demonstrated in vitro. Miller & Dawson (1972a) also demonstrated the ability of synaptic vesicles to synthesize phosphatidylcholine from CDP-choline and sn-1,2-diacylglycerol.…”