Biomass is an interesting starting material for transportation fuels because of its renewable nature. The main constituents of biomass are the carbohydrate polymers cellulose and hemi-cellulose, and lignin. Current transportation fuels are mixtures of mainly hydrocarbons derived from crude oil. Biomass derived biofuels are preferably used as blends with fossil fuels to avoid the need for adaptations in the existing car fleet. The total blend then needs to meet the set fuel specifications for fossil fuels. The conversion of biomass to biofuels therefore centres on the removal of oxygen from carbohydrates to obtain hydrocarbons. Oxygen is preferably eliminated in the form of CO 2 or H 2 O, because the heat of combustion of these molecules is zero and all energy is concentrated in the remaining products. Based on gross chemical formulae, the conversion options from biomass to biofuels have been investigated, and interesting intermediates have been identified. Conversion routes from carbohydrates to hydrocarbons tend to proceed via C 1 -intermediates (CO, CH 4 and carbon). Gasification and subsequent Fischer Tropsch synthesis seems the logical processing route to obtain hydrocarbons from biomass via these intermediates. If oxygen containing products are allowed, conversion can proceed via larger intermediates. For blending with gasoline, ethanol emerges as an interesting component. Longer carbon chain molecules are required for diesel. These can only be obtained by at least two process steps, involving the combination of carbon chains (e.g. by etherification or esterification), and reduction of polarity (by hydrogenation or oligomerisation). The lignin present in biomass has a complex, highly cross-linked structure, and can probably best be converted to syngas via gasification or applied directly as solid fuel.

Plants continuously have to defend themselves against life-threatening events such as drought, mechanical damage, temperature stress, and potential pathogens. Nowadays, more and more similarities between the defense mechanism of plants and that of animals are being discovered. In both cases, the lipoxygenase pathway plays an important role. In plants, products of this pathway are involved in wound healing, pest resistance, and signaling, or they have antimicrobial and antifungal activity. The first step in the lipoxygenase pathway is the reaction of linoleic or linolenic acids with molecular oxygen, catalyzed by the enzyme lipoxygenase. The hydroperoxy fatty acids thus formed are highly reactive and dangerous for the plant and therefore further metabolized by other enzymes such as allene oxide synthase, hydroperoxide lyase, peroxygenase, or divinyl ether synthase. Recently, these enzymes have been characterized as a special class of cytochrome P450 enzymes. Hydroperoxide lyases cleave the lipoxygenase products, resulting in the formation of omega-oxo acids and volatile C6- and C9-aldehydes and -alcohols. These compounds are major contributors to the characteristic "fresh green" odor of fruit and vegetables. They are widely used as food flavors, for example, to restore the freshness of food after sterilization processes. The low abundance of these compounds in nature and the high demand make it necessary to synthesize them on a large scale. Lipoxygenase and hydroperoxide lyase are suitable biocatalysts for the production of "natural" food flavors. In contrast to lipoxygenase, which has been extensively studied, little is yet known about hydroperoxide lyase. Hydroperoxide lyases from different organisms have been isolated, and a few genes have been published lately. However, the structure and reaction mechanism of this enzyme are still unclear. The identification of this enzyme as a cytochrome P450 sheds new light on its structure and possible reaction mechanism, whereas recombinant expression brings a biocatalytic application into sight.

Saturated and unsaturated N-acylethanolamines (NAEs) occur in desiccated seeds primarily as 16C and 18C species with N-palmitoylethanolamine and N-linoleoylethanolamine (NAE 18:2) being most abundant. Here, we examined the metabolic fate of NAEs in vitro and in vivo in imbibed cotton (Gossypium hirsutum) seeds. When synthetic [1-14 C]Npalmitoylethanolamine was used as a substrate, free fatty acids (FFA) were produced by extracts of imbibed cottonseeds. When synthetic [1-14 C]NAE 18:2 was used as a substrate, FFA and an additional lipid product(s) were formed. On the basis of polarity, we presumed that the unidentified lipid was a product of the lipoxygenase (LOX) pathway and that inclusion of the characteristic LOX inhibitors nordihydroguaiaretic acid and eicosatetraynoic acid reduced its formation in vitro and in vivo. The conversion of NAE 18:2 in imbibed cottonseed extracts to 12-oxo-13-hydroxy-N-(9Z)-octadecanoylethanolamine was confirmed by gas chromatography-mass spectrometry, indicating the presence of 13-LOX and 13-allene oxide synthase, which metabolized NAE 18:2. Cell fractionation studies showed that the NAE amidohydrolase, responsible for FFA production, was associated mostly with microsomes, whereas LOX, responsible for NAE 18:2-oxylipin production, was distributed in cytosol-enriched fractions and microsomes. The highest activity toward NAE by amidohydrolase was observed 4 to 8 h after imbibition and by LOX 8 h after imbibition. Our results collectively indicate that two pathways exist for NAE metabolism during seed imbibition: one to hydrolyze NAEs in a manner similar to the inactivation of endocannabinoid mediators in animal systems and the other to form novel NAE-derived oxylipins. The rapid depletion of NAEs by these pathways continues to point to a role for NAE metabolites in seed germination.In mammalian cells, N-acylethanolamines (NAEs) have varied physiological roles. N-Arachidonylethanolamine (anandamide), a type of NAE in mammalian brain tissue, is an endogenous ligand for the cannabinoid receptor and modulates neurotransmission. Anandamide also can activate vanilloid (capsaicin) receptors and function as an endogenous analgesic (Pertwee, 2001), and appears to be involved in neuroprotection (Hansen et al., 2000;Van der Stelt et al., 2001). In other animal tissues, NAEs have been implicated in immunomodulation (Buckley et al., 2000), synchronization of embryo development (Paria and Dey, 2000), and induction of apoptosis (Sarker et al., 2000). These endogenous bioactive molecules termed "endocannabinoids" are hydrolyzed by fatty acid amidohydrolase (AHase) to terminate their signaling functions.In plants NAEs are present in substantial amounts in desiccated cotton (Gossypium hirsutum) seeds (1.6 g Ϫ1 g fresh weight), and their levels decline after a few hours of imbibition . Individual NAEs were identified predominantly as 16C and 18C species with N-palmitoylethanolamine (NAE 16:0) and N-linoleoylethanolamine (NAE 18:2) being the most abundant. NAEs in both plant and animal cells are deri...

Nisin is an amphiphilic peptide with a strong antimicrobial activity against various Gram-positive bacteria. Its activity results from permeabilization of bacterial membranes, causing efflux of cytoplasmic compounds. To get information on the molecular mechanism of membrane permeabilization, a mutant of nisin Z containing the C-terminal extension Asp-(His)6 was produced. The biological and anionic lipid-dependent membrane activity of this peptide was very similar to that of nisin Z. Analysis of the pH dependence of model membrane interactions with the elongated peptide indicated the importance of electrostatic interactions of the C-terminus with the target membrane for membrane permeabilization. Most importantly, the membrane topology of the C-terminus of the molecule could be determined by trypsin digestion experiments, in which trypsin was encapsulated in the lumen of large unilamellar vesicles. The results show that the C-terminal part of the peptide translocates across model membranes. The pH and anionic lipid dependence of translocation closely paralleled the results of membrane permeabilization studies. Binding of nickel ions to the histidines blocked translocation of the C-terminus and concomitantly resulted in a 4-fold reduced capacity to induce K+ leakage. The results demonstrate for the first time that pore formation of nisin involves translocation of the C-terminal region of the molecule across the membrane.

Three full-length cDNAs from alfalfa seedlings coding for hydroperoxide lyases were cloned and expressed in Escherichia coli and characterized as cytochrome P450 enzymes. The isoenzymes were specific for 13-hydroperoxy linoleic and linolenic acids and did not use the 9-hydroperoxy isomers as substrates. Because alfalfa contains both specificities, this indicates the presence of two different types of hydroperoxide lyases, each specific for one kind of substrate. The enzymes contain 480 amino acids (54 kDa) and contain an unusual, nonplastidic N-terminal sequence of 22 amino acids, which strongly reduces the enzyme activity. The only known presequence of a hydroperoxide lyase (from Arabidopsis thaliana) was considered to be a transit sequence. The reduced enzyme activity, however, indicates that the hydroperoxide lyases with N-terminal extensions could be pro-enzymes. This hypothesis is supported by the fast release of hydroperoxide lyase products by plants upon wounding. One of the isoenzymes showed a strongly decreased V max and K m compared to the other two. Because this is probably due to the substitution of Ser377 by Phe; the residue at position 377 seems to be important. This is the first time that sufficient quantities of hydroperoxide lyase have been obtained for characterization studies, by circumventing difficult purification procedures and degradation of the enzyme. The high expression level, easy purification, good stability and high specificity make these cloned hydroperoxide lyases excellent tools to study the reaction mechanism and structure. We postulate an integrated reaction mechanism, based on the known chemistry of cytochrome P450 enzymes. This is the first mechanism that unifies all observed features of hydroperoxide lyases.

Volatile C6- and C9-aldehydes and alcohols are widely used as food flavors to reconstitute the "fresh green" odor of fruits and vegetables lost during processing. To meet the high demand for natural flavors, an efficient, cheap, and versatile biocatalytic process was developed to produce C6-aldehydes on a large scale. Vegetable oils were converted by soybean lipoxygenase and recombinant hydroperoxide lyase into hexanal and (2E)- or (3Z)-hexenal. In contrast to plant extracts, generally used as enzyme sources, high molar conversions were obtained with recombinant hydroperoxide lyase (50% for hexanal and 26% for hexenal formation), and no side products were formed. Furthermore, recombinant hydroperoxide lyase lacks isomerase activity, allowing production of (3Z)-hexenal, which could not be obtained in previously described processes. Recombinant hydroperoxide lyase is stable and can be stored at 4 degrees C for 1 month without significant loss of activity.

Fatty acid hydroperoxides formed by lipoxygenase can be cleaved by hydroperoxide lyase resulting in the formation of short-chain aldehydes and g g-oxo acids. Plant hydroperoxide lyases use 13-or 9-hydroperoxy linoleic and linolenic acid as substrates. Alfalfa (Medicago sativa L.) has been reported to contain a hydroperoxide lyase specific for 13-hydroperoxy linoleic and linolenic acid only. However, in addition to 13-hydroperoxide lyase activity we found substantial 9-hydroperoxide lyase activity in alfalfa seedlings as well. The specific activity for 9-hydroperoxy fatty acids was about 50% of the activity for the 13-isomers. Furthermore, alfalfa seedlings contain a 3Z:2E-enal isomerase that converts the 3Z-enal products to their 2E-enal isoforms.z 1999 Federation of European Biochemical Societies.

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