John L. Harwood

Bio: John L. Harwood is an academic researcher from Cardiff University. The author has contributed to research in topics: Lipid metabolism & Fatty acid. The author has an hindex of 60, co-authored 420 publications receiving 16081 citations. Previous affiliations of John L. Harwood include John L. Scott & Spanish National Research Council.

On the origin of oil droplets in maturing castor bean seeds,Ricinus communis

Abstract: Fat droplets isolated from maturing castor bean seeds contain high concentrations of fatty acid synthetase and triglyceride synthesizing enzymes. These activities are not due to contamination by other organelles and account for at least 80% of the total lipid synthesis. Electron microscopy of the isolated oil droplets and the seed tissue in vivo revealed particulate containing vacuole-like inclusions which, it is suggested, are the site of lipid synthesis and which form the original locus of the droplet.

Effect of irrigation on quality attributes of olive oil.

Abstract: Two irrigation treatments were applied to olive trees of the major commercial Cretan variety cv. Koroneiki, (a) irrigation with 0.4 evaporation class “A” pan and (b) rain-feed only, in two successive crop years to assess the effect of irrigation on olive oil quality. Olive fruits were harvested at their semiblack maturity stage. Data obtained indicated that irrigation increased fruit weight and oil content, but the standard quality indices (free fatty acids, peroxide value, K232, and K270) of the oil were not affected significantly. However, irrigation affected some aspects of olive oil composition. There were changes in the proportions of polyunsaturated fatty acids (PUFAs), triacylglycerol molecular species, sterols, and aliphatic alcohols. Furthermore, the concentrations of the dialdehydic form of elenolic acid linked to 3,4-DHPEA (3,4-DHPEA-EDA) and the isomer of oleuropeine aglycon (3,4-DHPEA-EA) were higher in oils from non-irrigated trees. Tocopherol and total volatiles were higher in the oil produ...

Lipid composition of subcellular membranes from larvae and prepupae of Drosophila melanogaster.

Abstract: Subcellular membranes were analyzed for their lipid composition and protein content at two developmental points representing the third instar wandering larvae and prepupal stages of Drosophila. At both stages, phosphatidylethanolamine (PE) and phosphatidylcholine (PC) were the major constituents with phosphatidylinositol (PI), phosphatidylserine (PS), diphosphatidylglycerol (DPG) and phosphatidic acid (PA) being relatively minor components. In total homogenates and in the nuclear-enriched fraction there was no significant difference in the phospholipid composition of the wandering larvae and prepupae. In mitochondria only a significant increase in the minor component PS was observed in the prepupae. In lysosomal membranes on the other hand, the relative abundance of the major components PE and PC increased in the prepupae although the molar ratios of the two lipids remained almost constant. The fatty acid composition of the phospholipids remained virtually unchanged in all of the fractions examined, including the lysosomes, and there was no evidence of lipid peroxidation. With regard to cellular degeneration and the involvement of lysosomes, we conclude that mechanisms other than gross modification of the lipid and/or lipid/protein ratio of their membranes are involved in the liberation of the acid phosphatase contents.

Temperature-dependent changes in plasma-membrane lipid order and the phagocytotic activity of the amoeba Acanthamoeba castellanii are closely correlated.

Abstract: The relationship between temperature-dependent changes in phagocytotic activity of Acanthamoeba castellanii and the fatty acid composition and physical properties of plasma membrane-enriched fractions were determined in cultures acclimated to 30 degrees C and 15 degrees C. Chilling (from 30 degrees C to 15 degrees C) had a very pronounced short-term inhibitory effect on phagocytosis only in stationary-phase cultures, which displayed a low degree of fatty acid unsaturation. A subsequent increase in phagocytosis by these cells was correlated with a low-temperature-induced increase in fatty acid unsaturation (shown previously [Jones, Lloyd and Harwood (1993) Biochem. J. 296, 183-188] to be due to n-6 desaturase induction). Plasma membrane-enriched fractions from 15 degrees C-acclimated cells also showed a marked increase in the relative proportion of polyunsaturated fatty acids. Steady-state fluorescence depolarization studies, using the membrane probe diphenylhexatriene, revealed increases in plasma membrane order with decreasing assay temperature. Over the upper assay-temperature range (25-40 degrees C), fluorescence anisotropy values were higher in membranes from 30 degrees C-acclimated cells; a 3.3 degrees C relative displacement of plots indicated that temperature-induced changes in membrane lipid composition compensated for approx. 22% of the ordering effect of low temperature. Changes in the temperature-dependence of fluorescence anisotropy, possibly corresponding to lateral phase separations or alterations in other bulk physical properties of membranes, occurred between 20 and 25 degrees C in membranes from 30 degrees C-acclimated cells and between 15 and 20 degrees C in membranes from 15 degrees C-acclimated cells. Fluorescence anisotropy plots were superimposed at assay temperatures between 5 and 15 degrees C. Short-term phagocytotic rates in whole cells decreased with assay temperature. Arrhenius discontinuities in rates of phagocytosis occurred at approx. 25.0 degrees C and 17.5 degrees C in 30 degrees C- and 15 degrees C-acclimated cells respectively, and in each case were thus within the temperature ranges of slope-change in the corresponding fluorescence anisotropy plots. The results show a direct correlation between plasma membrane fatty acid unsaturation, membrane physical properties and phagocytotic activity in A. castellanii. Therefore, a specific integrated physiological process has been correlated with fatty acid desaturase induction for the first time.

Interferon-γ: an overview of signals, mechanisms and functions

Abstract: Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.

Microalgal triacylglycerols as feedstocks for biofuel production: perspectives and advances

Abstract: Microalgae represent an exceptionally diverse but highly specialized group of micro-organisms adapted to various ecological habitats. Many microalgae have the ability to produce substantial amounts (e.g. 20-50% dry cell weight) of triacylglycerols (TAG) as a storage lipid under photo-oxidative stress or other adverse environmental conditions. Fatty acids, the building blocks for TAGs and all other cellular lipids, are synthesized in the chloroplast using a single set of enzymes, of which acetyl CoA carboxylase (ACCase) is key in regulating fatty acid synthesis rates. However, the expression of genes involved in fatty acid synthesis is poorly understood in microalgae. Synthesis and sequestration of TAG into cytosolic lipid bodies appear to be a protective mechanism by which algal cells cope with stress conditions, but little is known about regulation of TAG formation at the molecular and cellular level. While the concept of using microalgae as an alternative and renewable source of lipid-rich biomass feedstock for biofuels has been explored over the past few decades, a scalable, commercially viable system has yet to emerge. Today, the production of algal oil is primarily confined to high-value specialty oils with nutritional value, rather than commodity oils for biofuel. This review provides a brief summary of the current knowledge on oleaginous algae and their fatty acid and TAG biosynthesis, algal model systems and genomic approaches to a better understanding of TAG production, and a historical perspective and path forward for microalgae-based biofuel research and commercialization.