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.

Metabolism of trans‐3‐Hexadecenoic Acid in Broad Bean

Abstract: 1 Broad bean (Vicia faba) leaves contain rather high concentrations (about 4% of total fatty acids) of the trans-3-hexadecenoic acid. 2 Amounts of the acid increase with the age of the leaves and are absent from etiolated tissue. 3 Changes in the levels of trans-Δ3-hexadecenoic acid can be produced by subjecting the intact plants to various light/dark periods. 4 Chloroplasts isolated from broad-bean leaves show high rates of fatty acid synthesis from [1-14C]acetate. Synthesis is dependent on coenzyme A and ATP but is insensitive to the addition of exogenous acyl carrier protein. 5 The pattern of acids made includes about 20% palmitic, 5% hexadecenoic, 10% stearic and 60% oleic. trans-3-Hexadecenoic acid synthesis was most active in chloroplasts from plants exposed to the dark for 5 days and light for 3 days. 6 Arsenite addition inhibited stearate formation by isolated chloroplasts but resulted in a two-fold stimulation of overall synthesis. 7 The rate of fatty acid synthesis by isolated chloroplasts paralleled the changes in endogenous trans-3-hexadecenoic acid levels in the leaves from which they were isolated.

Regulation and enhancement of lipid accumulation in oil crops: The use of metabolic control analysis for informed genetic manipulation

Abstract: Plant oils are a very valuable agricultural commodity. They are currently mainly used (>80%) for food and animal feed but, increasingly, they have utility as renewable sources of industrial feedstocks or biofuel. Because of finite agricultural land, the best way to increase availability (in order to match demand) is by improving productivity. To do this requires a knowledge of metabolism and its regulation. Various methods have been used to provide information but only systems biology can yield quantitative data about complete metabolic pathways. We have used metabolic control analysis to provide information about major oil crops such as oilseed rape, oil palm, olive, and soybean. Such knowledge has then been used to inform genetic manipulation for crop improvement.

Temperature-induced membrane-lipid adaptation in Acanthamoeba castellanii.

Abstract: A method has been developed for the separation of the major membrane fractions of Acanthamoeba castellanii after growth at different temperatures. The acyl-lipid compositions of individual membrane fractions, microsomal membranes, plasma membrane and mitochondria were analysed after a shift in culture temperature from 30 degrees C to 15 degrees C. The major change in lipid composition observed was an alteration in the relative proportions of oleate and linoleate. This reciprocal change was seen in all the membrane fractions, but occurred most rapidly in the phosphatidylcholine of the microsomal fraction. Thus, there appears to be a rapid induction of delta 12-desaturase activity in A. castellanii after a downward shift in growth temperature. Changes were also seen in the proportions of the n-6 C20 fatty acids, with a decrease in the proportions of icosadienoate and increases of icosatrienoate and arachidonate. However, unlike the alteration in oleate/linoleate ratios, this change was not seen in all the individual lipids of each membrane fraction.

Contrasting Effects of n-3 and n-6 Fatty Acids on Cyclooxygenase-2 in Model Systems for Arthritis

Abstract: Cyclooxygenase-2 (COX-2) is intimately involved in symptoms of arthritis while dietary n-3 polyunsaturated fatty acids (PUFA) are thought to be beneficial. In these experiments, using both bovine and human in vitro systems that mimic features of arthritis, we show that the n-3 PUFA eicosapentaenoic acid (EPA) is able to reduce mRNA and protein levels of COX-2. Activity, as assessed through prostaglandin E(2) formation, was also reduced in a dose-dependent manner. These effects of EPA contrasted noticeably with the n-6 PUFA, arachidonic acid. The data provide direct evidence for a molecular mechanism by which dietary n-3 PUFA, such as EPA, can reduce inflammation and, hence, associated symptoms in arthritis.

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.