Definition of the pathway for membrane phospholipid fatty acid turnover in human erythrocytes

Acylation of lysoglycerophospholipids by adrenal membranes

1. Substantial differences were found in the acyl donor and lyso-acceptor specificities among subcellular membranes and with respect to different regions of the adrenal gland. 2. In the presence of Mg2+-ATP and CoASH, adrenal microsomes were actively transferring arachidonate to lysophospholipids with acyl acceptor specificity in the order: 1-acyl-GPI greater than 1-acyl-GPC greater than 1-acyl-GP. However, when oleoyl-CoA was used, acyl acceptor specificity for the microsomal transferases was in the order: 1-acyl-GPC greater than 1-acyl-GP greater than 1-acyl-GPI. 3. Mitochondrial membranes had very low acyl transfer activity and they preferred 1-acyl-GPC over other lyso-acceptors. 4. The chromaffin granules were apparently lacking this type of activity.

Effect of albumin, low temperature and metabolic inhibitors on transport of fatty acids into cultured human leukemic myeloid cells

Radioactively-labelled palmitic acid was used to study the effects of albumin, low temperature and several inhibitors of metabolism on transport of fatty acids into cultured human leukemic myeloid cells. When serum or albumin were present in the medium, uptake of fatty acid by cells as well as its further incorporation into phospholipids and neutral lipids were considerably reduced. Uptake and metabolic utilization of this fatty acid was reduced at low temperature, in the presence or absence of albumin in the incubation medium. In absence of albumin, addition of iodoacetate, sodium cyanide or sodium azide had but little effect on the total uptake of fatty acids while metabolic utilization was reduced. When albumin was present, these inhibitors reduced both total uptake and incorporation into lipids. The data suggest that incorporation of the fatty acid into the outer layer of the cell membrane is controlled by the concentration of free, uncomplexed molecules of fatty acid adjacent to the cell surface. In the absence of albumin this is a fast reaction which reaches nearly maximal uptake in three minutes. In the presence of albumin, this process is much slower and follows a nearly linear course between 3 and 60 minutes. Translocation into the inner layer of the membrane and subsequent utilization for metabolic processes is a much slower process, which seems to depend on the quantity of the fatty acid in the outer layer.

Selective changes in fatty acid composition of phosphatidylserine in rat erythrocyte membrane induced by nitrate

The relationship between nitrate which is formed from inhaled nitrogen dioxide, a common air pollutant, and changes in fatty acid metabolism of phosphatidylserine in rat erythrocytes has been examined. When erythrocytes were incubated at 37 degrees C for 60 min with fatty acid, the incorporation rate of [1-14C]arachidonic acid and [9,10-3H]palmitic acid into phosphatidylserine was 15% (80 pmol/h per mumol lipid phosphorus) and 20% (12 pmol/h per mumol lipid phosphorus) of those into phosphatidylethanolamine, respectively. By the addition of 1.0 mM sodium nitrate or 0.5 microM ionophore A23187 to the incubation mixture, the rate of incorporation of both arachidonic acid and palmitic acid into phosphatidylethanolamine was stimulated 1.45-fold. On the other hand, the incorporation of palmitic acid into phosphatidylserine was little affected, while that of arachidonic acid was stimulated 1.35-fold. An increase in arachidonic acid of phosphatidylserine was also found by the addition of nitrate or ionophore A23187. This increase was dependent on the concentration of extracellular calcium and observed by the addition of other chaotropic anions in the order SCN- greater than ClO4- greater than NO3-. It seems likely, therefore, that nitrate causes changes in erythrocyte membranes to facilitate calcium uptake. Increasing the concentration of intracellular calcium may cause stimulation of acyl-CoA:lysophospholipid acyltransferase and/or endogenous phospholipase A2.

Transport of fluorescent derivatives of fatty acids into cultured human leukemic myeloid cells and their subsequent metabolic utilization

Transport of fluorescent derivatives of fatty acids across the cell membrane of cultured human leukemic myeloid cells (HL 60) and their subsequent metabolic utilization were studied. The rates of uptake of these derivatives and their incorporation into cellular lipids wer compared with that of radioactively labelled palmitic acid. Three groups of fluorescent derivatives were observed: A, those transported into the cells and subsequently incorporated into neutral lipids and phospholipids, B, fatty acids which were taken up by the cells but not utilized metabolically, and C, fatty acids which were not transported across the cell membrane. Fatty acids of the latter group, except the hydrophobic probe, also contained functional groups such as hydroxy, acetylamino or sulfonylamino. When observed in fluorescence microscopy, cells incubated with group A fatty acids contained intracellular fluorescent granules, whereas those incubated with group B fatty acids showed diffuse fluorescence. HL 60 cells undergo differentiation into granulocytes or macrophages upon treatment with dimethylsulfoxide or a phorbol ester, respectively. When compared to the uninduced cells, the transport of the fluorescent fatty acids or palmitic acid as well as their subsequent incorporation into lipids were considerably lower in the granulocytes and higher in the macrophages. The use of the fluorescent derivatives as a tool for studying transport of fatty acids across the cell membrane is discussed.

On the mechanisms of fatty acid transformations in membranes

Concentrations of albumin in excess of 1% in the incubation mixture inhibited the elongation of added fatty acids and their incorporation into microsomal lipids whereas these reactions were not inhibited with endogenous microsomal membrane fatty acids. The results of these and other studies support the idea that such reactions of membrane lipid fatty acids with membrane-bound enzymes normally occur entirely within the membrane without release of free fatty acids to equilibrate with the fatty acid pool during the process.