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.

Plant lipid biosynthesis : fundamentals and agricultural applications

Abstract: Preface 1. What's so special about plant lipids? J. Harwood 2. Biotin-dependent carboxylases and their biotinylation in higher plants C. Alban and R. Douce 3. Down-regulation of lipid synthesis in plants implies higher orders of regulation in fatty acid biosynthesis A. White, K. Elborough, S. Hanley, A. Slabas 4. Molecular structure of a reductase component of fatty acid synthase C. Baldock, J. Rafferty, A. Stuitje and D. Rice 5. Fatty acid desaturases: structure, mechanism and regulation D. Murphy and P. Piffanelli 6. Altering the fatty acid composition of vegetable oils J. Browse, J. Spychalla, J. Okuley and J. Lightner 7. Engineering frost-resistance in plants by genetic manipulation P. Quinn 8. Recent advances in plant fatty acid elongation F. Domergue, J.-J. Bessoule, P. Moreau, R. Lessire and C. Cassagne 9. Triacylglycerol biosynthesis A. Stobart, S. Stymne, P. Shewry and J. Napier 10. Molecular biology of acyltransferases involved in glycerolipid synthesis M. Frentzen and F. Wolter 11. Production of specialised oils for industry A. Kinney 12. Manipulating seed oils for polyunsaturated fatty acid content D. Knutson and V. Knauf 13. Environmental effects on plant lipid biochemistry J. Harwood 14. The future: industry requirements from advances in plant lipid research S. Bright and T. Hawkes Index.

Light-Induced Changes in Fatty Acid Profiles of Specific Lipid Classes in Several Freshwater Phytoplankton Species

Abstract: We tested the influence of two light intensities [40 and 300 µmol PAR / (m² s)] on the fatty acid composition of three distinct lipid classes in four freshwater phytoplankton species. We chose species of different taxonomic classes in order to detect potentially similar reaction characteristics that might also be present in natural phytoplankton communities. From samples of the bacillariophyte Asterionella formosa, the chrysophyte Chromulina sp., the cryptophyte Cryptomonas ovata and the zygnematophyte Cosmarium botrytis we first separated glycolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylethanol-amine, phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine) as well as non-polar lipids (triacylglycerols), before analyzing the fatty acid composition of each lipid class. High variation in the fatty acid composition existed among different species. Individual fatty acid compositions differed in their reaction to changing light intensities in the four species. Although no generalizations could be made for species across taxonomic classes, individual species showed clear but small responses in their ecologically-relevant omega-3 and omega-6 polyunsaturated fatty acids in terms of proportions and of per carbon quotas. Knowledge on how lipids like fatty acids change with environmental or culture conditions is of great interest in ecological food web studies, aquaculture and biotechnology, since algal lipids are the most important sources of omega-3 long-chain polyunsaturated fatty acids for aquatic and terrestrial consumers, including humans.

Use of metabolic control analysis to give quantitative information on control of lipid biosynthesis in the important oil crop, Elaeis guineensis (oilpalm)

Abstract: Summary • Oil crops are a very important commodity. Although many genes and enzymes involved in lipid accumulation have been identified, much less is known of regulation of the overall process. To address the latter we have applied metabolic control analysis to lipid synthesis in the important crop, oilpalm (Elaeis guineensis). • Top-down metabolic control analysis (TDCA) was applied to callus cultures capable of accumulating appreciable triacylglycerol. The biosynthetic pathway was divided into two blocks, connected by the intermediate acyl-CoAs. Block A comprised enzymes for fatty acid synthesis and Block B comprised enzymes of lipid assembly. • Double manipulation TDCA used diflufenican and bromooctanoate to inhibit Block A and Block B, respectively, giving Block flux control coefficients of 0.61 and 0.39. Monte Carlo simulations provided extra information from previously-reported single manipulation TDCA data, giving Block flux control coefficients of 0.65 and 0.35 for A and B. • These experiments are the first time that double manipulation TDCA has been applied to lipid biosynthesis in any organism. The data show that approaching two-thirds of the total control of carbon flux to lipids in oilpalm cultures lies with the fatty acid synthesis block of reactions. This quantitative information will assist future, informed, genetic manipulation of oilpalm.

Fatty acid biosynthesis by a particulate preparation from germinating pea.

Abstract: 1. Fatty acid synthesis was studied in microsomal preparations from germinating pea (Pisum sativum). 2. The preparations synthesized a mixture of saturated fatty acids up to a chain length of C24 from [14C]malonyl-CoA. 3. Whereas hexadecanoic acid was made de novo, octadecanoic acid and icosanoic acid were synthesized by elongation. 4. The products formed during [14C]malonyl-CoA incubation were analysed, and unesterified fatty acids and polar lipids were found to be major products. [14C]Palmitic acid represented a high percentage of the acyl-carrier protein esters, whereas 14C-labelled very-long-chain fatty acids were mainly present as unesterified fatty acids. CoA esters were minor products. 5. The addition of exogenous lipids to the incubation system usually resulted in stimulation of [14C]malonyl-CoA incorporation into fatty acids. The greatest stimulation was obtained with dipalmitoyl phosphatidylcholine. Both exogenous palmitic acid and dipalmitoyl phosphatidylcholine increased the amount of [14C]-stearic acid synthesized, relative to [14C]palmitic acid. Addition of stearic acid increased the amount of [14C]icosanoic acid formed. 6. [14C]Stearic acid was elongated more effectively to icosanoic acid than [14C]stearoyl-CoA, and its conversion was not decreased by addition of unlabelled stearoyl-CoA. 7. Incorporation of [14C]malonyl-CoA into fatty acids was markedly decreased by iodoacetamide and 5,5′-dithiobis-(2-nitrobenzoic acid). Palmitate elongation was sensitive to arsenite addition, and stearate elongation to the presence of Triton X-100 or fluoride. The action of fluoride was not, apparently, due to chelation. 8. The microsomal preparations differed from soluble fractions from germinating pea in (a) synthesizing very-long-chain fatty acids, (b) not utilizing exogenous palmitate–acyl-carrier protein as a substrate for palmitate elongation and (c) having fatty acid synthesis stimulated by the addition of certain complex lipids.

The regulation of triacylglycerol biosynthesis in cocoa (Theobroma cacao) L.

Abstract: Developing cocoa cotyledons accumulate initially an unsaturated oil which is particularly rich in oleate and linoleate. However, as maturation proceeds, the characteristic high stearate levels appear in the storage triacylglycerols. In the early stages of maturation, tissue slices of developing cotyledons (105 days post anthesis, dpa) readily accumulate radioactivity from [14C]acetate into the diacylglycerols and label predominantly palmitate and oleate. In older tissues (130 dpa), by contrast, the triacylglycerols are extensively labelled and, at the same time, there is an increase in the percentage labelling of stearate. Thus, the synthesis of triacylglycerol and the production of stearate are co-ordinated during development. The relative labelling of the phospholipids (particularly phosphatidylcholine) was rather low at both stages of development which contrasts with oil seeds that accumulate a polyunsaturated oil (e.g. safflower). Microsomal membrane preparations from the developing cotyledons readily utilised an equimolar [14C]acyl-CoA substrate (consisting of palmitate, stearate and oleate) and glycerol 3-phosphate to form phosphatidate, diacylglycerol and triacylglycerol. Analysis of the [14C]acyl constituents at the sn-1 and sn-2 positions of phosphatidate and diacylglycerol revealed that the first acylase enzyme (glycerol 3-phosphate acyltransferase) selectively utilised palmitate over stearate and excluded oleate, whereas the second acylase (lysophosphatidate acyltransferase) was highly selective for the unsaturated acyl-CoA. On the other hand, the third acylase (diacylglycerol acyltransferase) exhibited an almost equal selectivity for palmitate and stearate. Thus, stearate is preferentially enriched at position sn-3 of triacylglycerol at 120–130 dpa because of the relatively higher selectivity of the diacylglycerol acyltransferase for this fatty acid compared with those of the other two acylation enzymes.

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.