Showing papers in "Advances in lipid research in 1970"

Plant Phospholipids and Glycolipids

Abstract: Publisher Summary This chapter describes the composition and cellular distribution of plant phospholipids and glycolipids and their cellular metabolism. Early studies on the lipids of plants had revealed only the presence of components well known in animal tissues, namely, phosphatidylcholine (lecithin), phosphatidylethanolamine and phosphatidylserine (cephalins), and phosphatidylinositol. Phosphatidic acid had been isolated from plant tissue and was considered to be a characteristic plant phosphatide, but this component was subsequently shown to be largely an artifact formed by enzymatic degradation during extraction of the lipids. Distribution of unsaturated fatty acids among the phospholipid and glycolipid components of both photosynthetic and nonphotosynthetic tissues is by no means uniform. In general, the galactolipids have very high contents of linolenic and C16 -trienoic acids in photosynthetic tissues grown in the light, or linoleic acid in nonphotosynthetic tissues. Phospholipids and glycolipids exist in a dynamic state of equilibrium in the membrane structures of plant cells, as may be readily demonstrated in studies using radioisotopes. Rapid incorporation of radioisotopes observed when plants cells are exposed to labeled presursors such as phosphate- 32P or 14CO2 is the result of a steady-state cycle of degradative and synthesizing reactions.

The essential fatty acids.

Abstract: Publisher Summary This chapter explains structural requirements, metabolism of action, and the role of the essential fatty acids. These acids are metabolized in ways common to other unsaturated fatty acids. In addition, the unsaturated acids possessing the 9, 12 double bond system (C18 acids) or the 11–14 double bond system (C20 acids) possesses special properties that are essential to the animal. Presumably, they function in esterified forms rather than as free fatty acids, and their essential roles may be determined by relative concentrations of phospholipids, glycerides, and sterol esters, which in turn seem to involve hormonal regulation. There is evidence to suggest that they are concerned, via phospholipids, in membrane integrity. This may be related to certain biochemical lesions that have been reported in connection with a deficiency of essential fatty acids in cases where membranes possess recognized biochemical activity, for example, in mitochondria. The essential fatty acids are the precursors of the prostaglandins, but the relationships of the latter to the classical deficiency symptoms is not certain and there is no evidence suggesting a relationship of this hormone family to the reported biochemical lesions of the deficiency.

Metabolism of long chain fatty acids in the rumen

Abstract: Publisher Summary This chapter discusses the metabolism of long-chain fatty acids in the rumen. The studies described in the chapter reveal the importance of veterinary problems in stimulating new interest in biochemical processes that might improve foods of animal origin and, thus, human nutrition. They have contributed to one of the most interesting areas of biochemical studies: the molecular basis of evolution. They have allowed the discovery of living biochemical fossils and have helped to elucidate the mechanisms of branched fatty acid biosynthesis and unsaturated fatty acid biohydrogenation. Studies on the origin of petroleum in association with studies on biological evolution show that branched-chain hydrocarbon structures derive from the corresponding fatty acid molecules. In fatty acid biohydrogenation, the enzyme responsible for the disappearance of a π bond probably represents a vestige, whose deep biological meaning is now hidden in the rumen, of the mechanisms of energy transformations of primitive organisms, when there was no oxygen in the atmosphere, at the beginning of life on earth.

Arterial composition and metabolism: esterified fatty acids and cholesterol.

Abstract: Publisher Summary This chapter discusses the composition and metabolism of arteries to an understanding of the degeneration of esterified fatty acids and cholesterol. It is possible to distinguish the morphological changes that occur in arteries with age and with atherosclerosis from changes that occur in the chemical composition of the arterial wall. Some progress has been made in explaining changes in the chemical composition through biochemical mechanisms and through the prevalence of different subcellular components, each with its own characteristic composition. Hyperlipemia is not the only mechanism for inducing lesions that indiscriminately take up cholesterol esters from plasma, and hyperlipemia is not required to maintain a net uptake of cholesterol esters once advanced atherosclerotic lesions are established. Cholesterol esters perhaps accumulate in advanced lesions because they are the most prevalent nonpolar constituents of low density lipoproteins. The increase in lecithin concentrations in aortic tissue with experimental atherosclerosis is apparently not an early change and may be considered in association with the second stage in atherogenesis. The increase in lecithin concentrations may be secondary to increased lysolecithin concentrations and increased rates of lysolecithin acylation in the arterial tissue. The increased lysolecithin concentrations in aorta are in part the result of increased concentrations and rates of formation of lysolecithin in plasma. It seems likely that the most interesting and, perhaps, fruitful investigations of arterial lipids in the future will involve the early biochemical and ultrastructural changes prior to the development of the overt morphological changes of atherosclerosis.

Cholesterol Turnover in Man

Abstract: Publisher Summary This chapter provides an overview of cholesterol turnover in man. The magnitude of cholesterol turnover and the factors that regulate it differ among different tissues; some of these factors are unique for a specific tissue yet are not identical in the same tissue in all mammalian species. The heterogeneous nature of cholesterol metabolism emphasizes the oversimplification that is inherent in attempts to measure and quantitate cholesterol turnover in an entire organism. The modes of action of a number of cholesterol-lowering drugs have been studied in man by measuring cholesterol turnover. The various techniques for the measurement of cholesterol turnover are ideally suited for the definition of the overall modes of action of these drugs in the entire living organism. Techniques that merely require measurement of plasma cholesterol specific activity are simpler to perform, but they do not answer the questions that can be solved by direct quantitation of fecal steroids or by a combination of the two methods. The following are the different techniques and the information that they have provided: (1) plasma specific activity-time curve analysis, (2) isotope sterol balance methods, (3) chromatographic techniques, and (4) turnover of bile acids.

Surface Chemistry of Lipids1

Abstract: Publisher Summary This chapter discusses surface chemistry and biochemical implications of lipids. It has long been recognized that lipids, proteins, and metal ions are major components of biological membranes. The monolayer provides a suitable system for the study of lipid–lipid, lipid–protein, and lipid–metal ion interactions, employing surface pressure, potential, viscosity, and radioactivity techniques. The increasing unsaturation of fatty acyl chains increases the intermolecular spacing and the rate of hydrolysis by phospholipase A, while it decreases the binding of metal ions and influences the ionic structure of lecithin monolayers. The molar ratio of cholesterol to phospholipids in erythrocyte or myelin membrane has been reported to be close to unity. Although electron microscopy has contributed much in revealing the ultrastructural organization of cells, there remains a considerable need to study the effect of heavy metals and fixatives on biological structures.

Lipids in membrane development.

Abstract: Publisher Summary This chapter explores lipids and their role in membrane development. The study of the role of lipids is primarily concerned with the synthesis of the bacterial cell wall and the lipopolysaccharides has any definition of some of the possible roles emerged. These two cases exemplify the great value that remains to be obtained from the investigation of the appropriate biochemical mutants of microorganisms in which there is some disturbance of membrane assembly. The use of mutants for the study of the morphogenesis of the bacteriophage particle has provided a beautiful illustration of this principle. It is now becoming quite clear that polar lipid classes exhibit considerable heterogeneity of composition, metabolism, and turnover even perhaps within the same polar lipid molecule. The possibility of ready exchange of many phospholipids between membranes, now demonstrated at least in vitro in the case of mitochondrial and microsomal membranes, has also to be borne in mind.