Physical studies of lipid-lipid and lipid-protein interactions

Vitamin E improves membrane lipid alterations induced by CCl4 intoxication

The effect of pretreatment with vitamin E on membrane lipid alterations produced by the acute intoxication with CCl4 was studied. Rats were treated with an oral dose of CCl4 (0.4 g per 100 g body weight) and 24 h later the animals were sacrificed and liver plasma membranes isolated. After extraction, the membrane lipids were analysed by thin-layer chromatography and quantitated by densitometry. The phospholipid: protein ratio determined in plasma membranes of CCl4-treated rats was almost three-fold higher than that found in control animals. Sphingomyelin (Sph) and phospharidyl choline (PC) increased, while phosphatidyl ethanolamine (PE) decreased in the plasma membranes isolated from the CCl4-treated group. Animals pretreated for 7 days with a daily dose of vitamin E (200 IU per kg body weight) showed a lower increase in the phospholipid: protein ratio (two-fold) and the changes in Sph, PC and PE were lower. When the rats were pretreated with a higher dose of vitamin E (400 IU per kg body weight) for the same period, the lipid composition of plasma membrane was normal. These results indicate that vitamin E can protect against the alterations induced by CCl4 on the liver membranes. The protective action of vitamin E against CCl4 membrane damage is probably associated with its antioxidant properties.

Cell growth with trans fatty acids is affected by adenosine 3',5'-monophosphate and membrane fluidity

Two positional isomers (9 and 11) of trans octadecenoates did not support growth on glucose of an Escherichia coli mutant that requires unsaturated fatty acids. However, the trans fatty acids provided sufficient fluidity to produce much higher cell yields when the concentration of adenosine 3',5'-monophosphate was raised. The effectiveness of the trans acids rose from 0 to 1 cell per femtomole to 15 to 20 cells per femtomole as the concentration of adenosine 3',5'-monophosphate was increased. The corresponding cis positional isomers supported high yields (35 to 40 cells per femtomole) independent of supplementation. The enhanced growth with adenosine 3',5'-monophosphate supplementation is not due to an increased uptake and incorporation of the trans isomers relative to the cis isomers, since the 9-trans isomer was incorporated more rapidly than the 9-cis isomer into the membrane phospholipids under all growth conditions and represented 21 +/- 2 mole percent of the acids. The finding that cells growing with trans fatty acid isomers have a higher requirement for adenosine 3',5'-monophosphate may indicate that some fatty acids can alter the metabolic regulation normally exerted by the cyclic nucleotide.

Brain neuraminidases and gangliosides

A number of data of kinetics nature indicate that brain neuraminidases (the cytosol and the membrane bound enzyme) recognize the physical state of gangliosidic substrate, with immediate modification of the activity. The interactions between the enzyme(s) and the different physical forms of the substrate are still to be studied at the molecular level. The knowledge of these phenomena would greatly help understanding the role played by gangliosides in the neuronal plasma membrane.

Effect of temperature acclimatization on the fatty acid composition of goldfish intestinal lipids

1. The fatty acid composition of whole goldfish, whole-intestinal mucosa, intestinal mucosal membranes and individual phospholipids extracted from mucosal membranes were measured, fish adapted to different temperatures being used. 2. Alterations of the adaptation temperature did not noticeably affect the fatty acid composition of the whole-fish lipids, but there were marked changes in the fatty acids of lipids extracted from homogenates of goldfish intestinal mucosa. These changes were more pronounced in a membrane fraction prepared from these homogenates. Raising the adaptation temperature by 20 degrees C halved the percentage of C(20:1), C(20:4) and C(22:6) fatty acids and nearly doubled the percentage of C(18:0) and C(20:3) fatty acids recovered. 3. Choline phosphoglycerides constituted about one-half and ethanolamine phosphoglycerides about one-quarter of the total membrane phospholipids. 4. The fatty acids of choline and ethanolamine phosphoglycerides were more susceptible to temperature-dependent changes than were the phosphoglycerides of inositol or serine. 5. The increase in C(18:0) fatty acid that occurred in membranes of warm-adapted fish was greatest for ethanolamine phosphoglycerides, but increases also occurred in other phospholipid fractions and in membrane neutral lipids.