Guy A. Thompson

Lipid-linked proteins of plants.

Increasing numbers of plant proteins are being shown to have posttranslationally-attached lipids. The modifications include N-myristoylation, S-palmitoylation, prenylation by farnesyl or geranylgeranyl moieties, or attachment of glycosylphosphatidylinositol anchors. This report summarizes recent findings regarding the structure, metabolism and physiological functions of these important protein-linked lipids.

Alpha Tocopherol Control of Sexuality and Polymorphism in the Rotifer Asplanchna

A dietary component that initiates both the tranisition from parthenogenetic to sexual reproduction and the production of lateral, posterodorsal, and posterior outgrowths of the body wall of females was isolated from the neutral lipids of dried grass and identified as α-tocopherol. The smallest concentrations eliciting both responses were below 100 nanograms per milliliter. Relative activities of α-, β3-, and γ-tocopherol and α-tocopheryl-quinone were roughly 100 : 100 : 20 : 0.4. The synthetic antioxidants tested were without activity.

Phosphonolipids: Localization in Surface Membranes of Tetrahymena

Approximately 60 percent of the phospholipids from the membrane sheath of Tetrahymena pyriformis cilia contain 2-aminoethylphosphonic acid. This is more than twice the concentration found in total cell lipids. The resistance of these lipids to hydrolytic enzymes suggests that they increase the stability of the surface membranes.

Retailored lipid molecular species: a tactical mechanism for modulating membrane properties

Abstract The particular arrangement of fatty acid pairs on polar lipid molecules, i.e. the lipid molecular species composition, may influence the physical and physiological properties of membranes constituted from those lipids. Recently developed analytical techniques have been used to demonstrate that intermolecular rearrangements of lipid acyl chains are important in bringing about significant fluidity-related changes in membranes in response to environmental stress as well as during normal metabolic events.

Novel aspects of the regulation of a cDNA (Arf1) from Chlamydomonas with high sequence identity to animal ADP-ribosylation factor 1

ADP-ribosylation factor (ARF) is a highly conserved, low molecular mass (ca. 21 kDa) GTP-binding protein that has been implicated in vesicle trafficking and signal transduction in yeast and mammalian cells. However, little is known of ARF in plant systems. A putative ARF polypeptide was identifed in subcellular fractions of the green alga Chlamydomonas reinhardtii, based on [32P]GTP binding and immunoblot assays. A cDNA clone was isolated from Chlamydomonas (Arf1), which encodes a 20.7 kDa protein with 90% identity to human ARF1. Northern blot analyses showed that levels of Arf1 mRNA are highly regulated during 12 h/12 h light/dark (LD) cycles. A biphasic pattern of expression was observed: a transient peak of Arf1 mRNA occurred at the onset of the light period, which was followed ca. 12 h later by a more prominent peak in the early to mid-dark period. When LD-synchronized cells were shifted to continuous darkness, the dark-specific peak of Arf1 mRNA persisted, indicative of a circadian rhythm. The increase in Arf1 mRNA at the beginning of the light period, however, was shown to be light-dependent, and, moreover, dependent on photosynthesis, since it was prevented by DCMU. We conclude that the biphasic pattern of Arf1 mRNA accumulation during LD cycles is due to regulation by two different factors, light (which requires photosynthesis) and the circadian clock. Thus, these studies identify a novel pattern of expression for a GTP-binding protein gene.

Environmentally produced alterations of the tetra-hymanol: Phospholipid ratio in Tetrahymena pyriformis membranes

Abstract Whereas the sterol-like triterpenoid tetrahymanol constitutes a fixed proportion of membrane lipids in growing and early stationary phase Tetrahymena cells, starved or senescent cultures increase their tetrahymanol-phospholipid ratios many fold. We detected two causes of tetrahymanol enrichment, both related to the absolute resistance of the compound to catabolic attack. Surviving cells of senescent cultures ingest fragments of dead cells, degrading the phospholipids but accumulating tetrahymanol in large amounts. On the other hand, growing cells placed in a nutrient-free medium receive no exogenous lipids. Rather, they gradually utilize their own structural components for energy, decreasing to 20% of their normal size during the process. There is a concomitant reduction of the cellular phospholipid content, but tetrahymanol is not degraded. Consequently, after 4 days of starvation the membrane tetrahymanol: phospholipid ratio is 3 times the normal value despite a virtual absence of tetrahymanol synthesis. We discuss the apparently successful adjustment of the cells to altered proportions of a lipid whose concentration is considered critical for proper membrane function.

Membrane acclimation by unicellular organisms in response to temperature change

Unicellular organisms possess a wide variety of molecular mechanisms for altering the lipid composition (and thereby the physical properties) of their membranes in response to changes in environmental temperature. These are discussed with a view to establish which of the mechanisms are of more importance to bacteria, algae, and protozoa in coping with extremes of temperature.

Effects of ethanol on fatty acid composition of muscle phospholipids of rats fed nutritionally complete liquid diets

Abstract Although the effects of ethanol on phospholipid fatty acid composition have been examined in single cell organisms and in rodents given ethanol as a vapor or in solution as sole drinking fluid, there are no reports of analogous experiments with nutritionally adequate liquid diets as the source of ethanol. In this experiment, young, 88 ± 5 g, male Sprague-Dawley rats given a nutritionally adequate liquid diet containing ethanol voluntarily consumed 12–18 g ethanol per kg body weight per day after 23 days. In 27 days with food intakes 64% of control, weight gains of ethanol-fed animals (group 2) were 50% of ad lib .-fed control animals (group 1) but 88% of isoenergetically pair-fed animals (group 3). Thus, energy in the ethanol diet was utilized for growth 88% as efficiently as isoenergetic diets containing dextrin. Liver and gastrocnemius muscle weights of group 2 were significantly lower than group 3 but brain weights were not similarly affected. Blood ethanol levels determined on days 14 and 24 were above 200 mg/dl at 10:00 p.m. and 7:00 a.m. but decreased to 50 mg/dl at 4:00 p.m. on a feeding schedule that began at 5:00 p.m. Dependence was confirmed by withdrawal symptomology. Compared to group 1, phospholipids isolated from gastrocnemius muscles of group 2 exhibited significant modifications in fatty acid composition. In ethanol-fed animals, 18:0 and 20:4 were lower, and 18:1 and 18:2 were higher, than ad lib .-fed controls. However, when group 2 was compared to group 3, the pair-fed control, there was no significant difference in fatty acid composition. The observed changes in fatty acid composition appear to have been due to the reduced food consumption that accompanied the model rather than to ethanol per se . These findings underline the importance of appropriate controls in liquid diet animal models of alcoholism.

Action of a homogeneous hydrogenation catalyst on living Tetrahymena mimbres cells

Various conditions were tested in an attempt to hydrogenate the unsaturated fatty acids of living Tetrahymena mimbres with the homogeneous catalyst palladium di-(sodium alizarine monosulfonate) without causing serious damage to the cells. Using a low (20 micrograms/ml) catalyst concentration in the external medium, hydrogenation of greater than 20% of surface membrane lipid double bonds were obtained, but hydrogenation of intracellular membranes was minimal. When exposed to H2, cells preincubated with inactive catalyst for several hours and visibly loaded with the catalyst lost viability as soon as hydrogenation exceeded trace levels. Material secreted by Tetrahymena into their medium effectively inhibited hydrogenation of added oleic acid, normally a good substrate. Mucus secreted by the cells, soluble proteins isolated from cell homogenates, bovine serum albumin, and cysteine were also inhibitory, but the inhibition could be overcome by employing higher catalyst concentrations. Although some enzymatic retroconversion of saturated lipids back to unsaturated lipids appeared to take place, the scale of the conversion was small, and further experimentation will be required to understand the mechanism involved. The selective hydrogenation of surface membranes achieved by these methods may be especially useful to those interested in fluidity effects on plasma membrane properties.

Ether-containing lipids of the slime mold,Physarum polycephalum: I. Characterization and quantification.

Rapidly growing plasmodia of the acellular slime mold,Physarum polycephalum, contain large amounts of ether-linked lipids. The ether bonds occur principally in the phospholipids, where plasmalogens account for 21–24 mole per cent of the total and alkyl ether phospholipids comprise 12 mole per cent of the total. Plasmalogens account for over half of the ethanolamine phosphatides, while the alkyl ether derivatives are more uniformly distributed among the various phospholipid fractions. The 16 carbon side chain is by far the major component of both the saturated and the α,β-unsaturated ether derivatives. The nature and amounts of ether lipids present inPhysarum add to the growing evidence that Myxomycetes are more closely related to protozoa than to fungi.