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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.


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Reference EntryDOI
23 Jun 2014
TL;DR: This chapter describes the most useful methods currently in use including the use of isotopes to study metabolism, as well as prospects for useful future developments.
Abstract: Lipids are vital constituents of cells – as membrane components, energy stores, signaling molecules, and surface compounds. In this article, we describe major lipids, how they can be extracted, and precautions in their handling. Specific methods for lipid analysis including radioisotope work, thin‐layer and gas–liquid chromatography and mass spectroscopy are then described and discussed.

1 citations

Journal ArticleDOI
TL;DR: Imipramine at these low dose levels appeared specific in its effect in promoting surfactant accumulation in the absence of other toxic effects.
Abstract: The tricyclic antidepressant imipramine was instilled directly onto the lung surface of experimental rats in specific low doses (0.025 - 0.60 mg/kg body weight) and the animals were sacrificed at time intervals from 2 - 21 days after a single instillation. Such treatment caused changes almost exclusively confined to the alveolar surface. Alterations were induced in the free cell numbers and lung lavage protein levels while alveolar lipid and pulmonary surfactant levels were elevated. All such changes could be considered indicative of a mild toxic reaction. Imipramine at these low dose levels appeared specific in its effect in promoting surfactant accumulation in the absence of other toxic effects.

1 citations

Journal ArticleDOI
TL;DR: The present study was expanded to include a number of systems in vitro to increase the knowledge of reaction details, and metronidazole was found to inhibit linoleate, but not oleate, desaturation in this tissue.
Abstract: A number of inhibitors have been used as probes in characterizing details of plant fatty acid synthesis. These include such molecules as arsenite, cerulenin, cyanide, fluoride and thiocarbamate herbicides (cf. Harwood, 1979). In order to increase our knowledge of reaction details, we began work with metronidazole (2-methylS-nitroimidazole1-ethanol), a drug widely used clinically for the treatment of diseases caused by anaerobic bacteria and protozoa (Gruneberg & Titsworth, 1973). This compound has been suggested to be a rather specific inhibitor of reactions using reduced ferredoxin and, accordingly, it was expected to inhibit desaturation of stearate to oleate (a reaction apparently requiring ferredoxin as the usual source of reduced equivalents; Jacobsen et al., 1974). Initially, metronidazole was tested in two plant systems in vivo-germinating pea (Pisum satiuum) and saillower (Carthamus tinctorius) seeds. When allowed to imbibe [\"Clacetate, these two kinds of seeds synthesized rather different patterns of fatty acids in the first 24 h of germination. Saillower synthesized 34% palmitate and 5 1% oleate of the total 14C-labelled fatty acids, whereas pea synthesized only saturated fatty acids (33% palmitate, 67% stearate). As expected, metronidazole strongly inhibited the formation of I1'Cloleate by saillower, but, surprisingly, also altered the pattern of I4Clabelled fatty acids made by pea. Thus, for example, the ratio of [14C]palmitate/[14C]stearate increased from 0.5 to 1.0 with 20 mM metronidazole in pea without the total incorporation of radioactivity into fatty acids being appreciably affected. A third system tested in vivo was the cucumber (Cucumis sativus) cotyledon. When incubated with ''C-labelled fatty acids, this tissue exhibits high rates of oleate and linoleate desaturation (Murphy et al., 1980). Metronidazole was found to inhibit linoleate, but not oleate, desaturation in this tissue. Because of the unexpected inhibition of palmitate elongation by metronidazole, the present study was expanded to include a number of systems in vitro. A direct test of metronidazole against the ferredoxin-requiring spinach chloroplast stearoyl(acyl carrier protein) (ACP) desaturase showed a high amount of inhibition (Table 1). This inhibition was also seen with the alternative electron donor, flavodoxin. When chloroplasts were prepared from cucumber cotyledons and incubated with [I4Clacetate, palmitate and oleate were essentially the only fatty acids synthesized. In the presence of metronidazole, oleate synthesis was inhibited but, instead of [14Clstearate building up, [14Clpalmitate was increased (Table 1). This indicated an inhibition of palmitate elongase such as had been observed in the germinating-pea system. The inhibition of palmitate elongase by metronidazole was further examined in the soluble fraction from germinating pea (Bolton & Harwood, 1977). The malonyl-CoA-dependent synthesis of stearate in this fraction was inhibited virtually completely by 2 mM-metronidazole (Table 1). At this concentration of inhibitor the total incorporation of radioactivity from [14Clmalonyl-CoA was still at 80% of the control value, indicating that fatty acid synthetase was unaffected. Since there was no evidence that ferredoxin was involved in palmitate elongation, it seemed possible that metronidazole was inhibiting the reaction by an oxidoreduction interaction with another component. Theoretically, the redox potential of NADH and NADPH should make them capable of reducing metronidazole, although a direct test could not show this (Chen & Blanchard, 1979). We tested a number of NADH or NADPH-requiring enzymes (e.g. lactate dehydrogenase, triose phosphate dehydrogenase, malate dehydrogenase, alcohol dehydrogenase) for metronidazole inhibition, but failed to record any noticeable effect. However, since the effect of metronidazole is not specific for ferredoxin, but will also occur with flavodoxin or the hydrogenase from Clostridium pasteurianum (Chen & Blanchard, 1979), we presume that the inhibition of palmitate elongase was due to the involvement of reduced equivalents of appropriate electronegativity in the reaction. Further studies are required to determine the nature of these reduced equivalents and the prevalence of metronidazole inhibition of different fatty acid elongations or desaturations.

1 citations


Cited by
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Journal ArticleDOI
Yusuf Chisti1
TL;DR: As demonstrated here, microalgae appear to be the only source of renewable biodiesel that is capable of meeting the global demand for transport fuels.

9,030 citations

Journal ArticleDOI
TL;DR: In this article, the transesterification reaction is aected by molar ratio of glycerides to alcohol, catalysts, reaction temperature, reaction time and free fatty acids and water content of oils or fats.

4,902 citations

Journal ArticleDOI
TL;DR: The current understanding of IFN‐γ ligand, receptor, ignal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophages function during infection are reviewed.
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.

3,589 citations

Journal ArticleDOI
TL;DR: 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 are provided.
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.

3,479 citations