Phytyl Side Chain Research Articles

Evidence of increases of phytol and chlorophyllide by enzymatic dephytylation of chlorophylls in smoothie made from spinach leaves.

Phytol is a diterpene alcohol found abundantly in nature as the phytyl side chain of chlorophylls. Free form of phytol and its metabolites have been attracting attention because they have a potential to improve the lipid and glucose metabolism. On the other hand, phytol is unfavorable for those who suffering from Refsum's disease. However, there is little information on the phytol contents in leafy vegetables rich in chlorophylls. This study indicated that raw spinach leaves contain phytol of 0.4-1.5mg/100g fresh weight. Furthermore, crude enzyme extracted from the leaves showed the enzyme activities involved in dephytylation of chlorophyll derivatives and they were high at mild alkaline pH and around 45°C, and lowered at 55°C or above. Under the optimum pH and temperature for such enzymes determined in the model reaction using the crude enzyme, phytol content in the smoothie made from raw spinach leaves increased with an increase of chlorophyllide, another reaction product. Comparison between the increased amounts of phytol and chlorophyllide showed that the enzymatic dephytylation of chlorophylls was critically responsible for the increase of phytol in the smoothie. PRACTICAL APPLICATION: Phytol, which is released by the enzymes related to chlorophyll metabolism in plants, has been investigated because of its potential abilities to improve the lipid metabolism and blood glucose level. In contrast to such health benefits, they are known to be toxic for patients suffering from Refsum's disease. This research for the first time reports the phytol content in raw spinach leaves and that phytol can be increased in the smoothie made from spinach leaves by the action of endogenous enzymes on chlorophyll derivatives under a certain condition. These results help control phytol content in the smoothies.

Use of Gas Chromatography-Mass Spectrometry Techniques (GC-MS, GC-MS/MS and GC-QTOF) for the Characterization of Photooxidation and Autoxidation Products of Lipids of Autotrophic Organisms in Environmental Samples.

This paper reviews applications of gas chromatography-mass spectrometry techniques for the characterization of photooxidation and autoxidation products of lipids of senescent phototrophic organisms. Particular attention is given to: (i) the selection of oxidation products that are sufficiently stable under environmental conditions and specific to each lipid class and degradation route; (ii) the description of electron ionization mass fragmentation of trimethylsilyl derivatives of these compounds; and (iii) the use of specific fragment ions for monitoring the oxidation of the main unsaturated lipid components of phototrophs. The techniques best geared for this task were gas chromatography-quadrupole-time of flight to monitor fragment ions with very high resolution and accuracy, and gas chromatography-tandem mass spectrometry to monitor very selective transitions in multiple reaction monitoring mode. The extent of the degradation processes can only be estimated if the oxidation products are unaffected by fast secondary oxidation reactions, as it is notably the case of ∆5-sterols, monounsaturated fatty acids, chlorophyll phytyl side-chain, and di- and triterpenoids. In contrast, the primary degradation products of highly branched isoprenoid alkenes possessing more than one trisubstituted double bond, alkenones, carotenoids and polyunsaturated fatty acids, appear to be too unstable with respect to secondary oxidation or other reactions to serve for quantification in environmental samples.

Diseases Due to the Deficiency in Vitamin K Conversion System and Its Prevention

Vitamin K is a fat-soluble vitamin that plays an important role in blood coagulation and bone formation. Vitamin K has homologues due to differences in the side chain structure, phylloquinone (abbreviated as vitamin K1, PK) having a phytyl side chain and menaquinones (MK-n, n=1 to 14) having an isoprenoid side chain structure. The main vitamin K that we take from our daily diet is PK, and a fermented food, natto, contains MK-7 produced by Bacillus subtilis natto. However, the majority of vitamin K present in the tissues of mammals, including humans, is menaquinone-4 (abbreviated as vitamin K2, MK-4) having a geranylgeranyl side chain. This reason is that PK or MK-n obtained in the diet is converted into MK-4 in the body. We identified that the UbiA prenyltransferase domain containing protein 1 (UBIAD1) is the conversion enzyme of PK and MK-n to MK-4. The physiological roles of MK-4 in all tissues of the whole body and the physiological significance of MK-4 converted from PK and MK-n by UBIAD1 have not been sufficiently elucidated yet. To investigate the function of UBIAD1 in vivo, we generated UBIAD1 systemic knockout mice and tissue-specific UBIAD1 knockout mice. In this paper, we introduce the usefulness of vitamin K for diseases that may involve vitamin K and UBIAD1.

Seasonal monitoring of lipid degradation processes in the western English Channel links bacterial 10S-DOX enzyme activity to free fatty acid production by phytoplankton

In a few recent studies, the action of a bacterial dioxygenase (10S-DOX) on palmitoleic acid was observed within some polar and estuarine settings. To add further mechanistic information regarding the action of this enzyme in marine settings, we measured a range of lipids (sterols, fatty acids and the chlorophyll phytyl side chain) and their biotic and abiotic degradation products in water samples collected in 2018 from two depths (5 m and 25 m) at the temperate oceanographic time series site L4, located in the western English Channel. Lipid distributions indicated a dominance of diatoms and copepods during the spring bloom, while a peak in dinoflagellate activity was evident in samples collected from late summer/autumn, both outcomes being consistent with taxonomic data reported previously for the same sampling site and interval. Monitoring of lipid oxidation products characteristic of different degradation pathways showed a relatively weak effect of photo- and autoxidation processes, with these acting mainly on the more reactive lipids (i.e. chlorophyll and polyunsaturated fatty acids). In contrast, monitoring of biotic degradation processes revealed significant quantities of 10S-hydroxyhexadec-8(E)-enoic acid in samples collected at the end of April (reaching 40% of the residual parent palmitoleic acid), attributed to the involvement of bacterial 10-dioxygenase (10S-DOX) activity during the spring bloom. We propose that this enzyme could be utilised by bacteria to detoxify free fatty acids released by wounded diatoms in the presence of copepods

A lil3 chlp double mutant with exclusive accumulation of geranylgeranyl chlorophyll displays a lethal phenotype in rice

BackgroundPhytyl residues are the common side chains of chlorophyll (Chl) and tocopherols. Geranylgeranyl reductase (GGR), which is encoded by CHLP gene, is responsible for phytyl biosynthesis. The light-harvesting like protein LIL3 was suggested to be required for stability of GGR and protochlorophyllide oxidoreductase in Arabidopsis.ResultsIn this study, we isolated a yellow-green leaf mutant, 637ys, in rice (Oryza sativa). The mutant accumulated majority of Chls with unsaturated geranylgeraniol side chains and displayed a yellow-green leaf phenotype through the whole growth period. The development of chloroplasts was suppressed, and the major agronomic traits, especially No. of productive panicles per plant and of spikelets per panicle, dramatically decreased in 637ys. Besides, the mutant exhibited to be sensitive to light intensity and deficiency of tocopherols without obvious alteration in tocotrienols in leaves and grains. Map-based cloning and complementation experiment demonstrated that a point mutation on the OsLIL3 gene accounted for the mutant phenotype of 637ys. OsLIL3 is mainly expressed in green tissues, and its encoded protein is targeted to the chloroplast. Furthermore, the 637ys 502ys (lil3 chlp) double mutant exclusively accumulated geranylgeranyl Chl and exhibited lethality at the three-leaf stage.ConclusionsWe identified the OsLIL3 gene through a map-based cloning approach. Meanwhile, we demonstrated that OsLIL3 is of extreme importance to the function of OsGGR, and that the complete replacement of phytyl side chain of chlorophyll by geranylgeranyl chain could be fatal to plant survival in rice.

Inhibition of angiotensin I converting enzyme by anacardic acids isolated from Cashew nut (Anacardium occidentale Linn.) shell liquid

ABSTRACTHypertension represents one of the most common maladies of western civilizations caused by bad dietary practices and lack of exercise. Angiotensin-I-converting enzyme inhibitors (ACEi) have been shown to be very efficient in the prevention of hypertension. ACEi are also implicated (by their ability to reduce the product of ACE activity namely angiotensin-II levels, which has oncogenic and increased cell proliferation effects) to be efficient anticancer agents. Therefore, we evaluated the potential antihypertension capacities of anacardic acids purified from Cashew (Anacardium occidentale Linn.) nut shell liquid by inhibition of ACE using analytical reverse-phase high performance liquid chromatography. The ability to inhibit ACE showed the following relation: anacardic-3 (IC50 = 12 µM) > anacardic acid-4 (IC50 = 20 µM) > anacardic acid-2 (IC50 = 33 µM) > anacardic acid-1 (IC50 = 39 µM) as compared to the positive control captopril (IC50 = 6.85 nM). Salicylic acid lacking a phytyl side chain was negative. The capacity of purified anacardic acids to inhibit ACE thereby represents the most potent naturally available plant chemicals described so far, as a potential means of reducing hypertension. The inhibition of angiotensin II production indicated that anacardic acids could also have utility in cancer prevention and recurrence, and reduction of cardiotoxicity during chemotherapy.

Monochromatic green light induces an aberrant accumulation of geranylgeranyled chlorophylls in plants

Light quality is an important environmental factor affecting the biosynthesis of photosynthetic pigments whose production seems to be affected not only quantitatively but also qualitatively. In this work, we set out to identify unusual pigment detected in leaves of barley (Hordeum vulgare L.) and explain its presence in plants grown under monochromatic green light (GL; 500–590 nm). The chromatographic analysis (HPLC-DAD) revealed that a peak belonging to this unknown pigment is eluted between chlorophyll (Chl) a and b. This pigment exhibited the same absorption spectrum and fluorescence excitation and emission spectra as Chl a. It was negligible in control plants cultivated under white light of the same irradiance (photosynthetic photon flux density of 240 μmol m−2 s−1). Mass spectrometry analysis of this pigment (ions m/z = 889 [M−H]−; m/z = 949 [M+acetic acid-H]-) indicates that it is Chl a with a tetrahydrogengeranylgeraniol side chain (containing two double bonds in a phytyl side chain; Chl aTHGG), which is an intermediate in Chl a synthesis. In plants grown under GL, the proportion of Chl aTHGG to total Chl content rose to approximately 8% and 16% after 7 and 14 days of cultivation, respectively. Surprisingly, plants cultivated under GL exhibited drastically increased concentration of the enzyme geranylgeranyl reductase, which is responsible for the reduction of phytyl chain double bonds in the Chl synthesis pathway. This indicates impaired activity of this enzyme in GL-grown plants. A similar effect of GL on Chl synthesis was observed for distinct higher plant species.

Monitoring abiotic degradation in sinking versus suspended Arctic sea ice algae during a spring ice melt using specific lipid oxidation tracers

The abiotic degradation state of sea ice algae released during a late spring ice melt process was determined by sampling the underlying waters and measuring certain well-known algal lipids and their oxidation products, including those derived from epi-brassicasterol, 24-methylenecholesterol, palmitoleic acid and the phytyl side-chain of chlorophyll. More specifically, parent lipids and some of their oxidation products were quantified in suspended (collected by filtration) and sinking (collected with sediment traps at 5 and 30m) particles from Resolute Passage (Canada) during a period of spring ice melt in 2012 and the outcomes compared with those obtained from related sea ice samples analyzed previously. Our data show that suspended cells in the near surface waters appeared to be only very weakly affected by photooxidative processes, likely indicative of a community of unaggregated living cells with high seeding potential for further growth. In contrast, we attribute the strong photooxidation state of the organic matter in the sediment traps deployed at 5m to the presence of senescent and somewhat aggregated sea ice algae that descended only relatively slowly within the euphotic zone, and was thus susceptible to photochemical degradation. On the other hand, the increased abiotic preservation of the sinking material collected in the sediment traps deployed at 30m, likely reflected more highly aggregated senescent sea ice algae that settled sufficiently rapidly out of the euphotic zone to avoid significant photooxidation. This better-preserved sinking material in the deeper sediment traps may therefore contribute more strongly to the underlying sediments. A three-component conceptual scheme summarizing the abiotic behavior of Arctic sea ice algae in underlying waters is proposed.

Autoxidation of chlorophyll phytyl side chain in senescent phototrophic organisms: A potential source of isophytol in the environment

In this short paper, it is demonstrated that autoxidation (free radical induced oxidation) of the chlorophyll phytyl side chain in senescent phytoplanktonic cells and higher plants constitutes a potential source of isophytol (3,7,11,15-tetramethylhexadec-1-en-3-ol) in the environment. To explain the formation of this isoprenoid alcohol, mechanisms involving the formation of the precursor 3-peroxy-3,7,11,15-tetramethylhexadec-1-ene are proposed.

Sequential photo- and autoxidation of diatom lipids in Arctic sea ice

We measured the concentrations of selected lipids and some of their degradation products in a time series of sea ice samples collected from Resolute Bay in the Canadian Arctic in 2012. The identification of specific tracers of photo- and autoxidation reactions provided evidence of both abiotic processes acting on organic matter, although none of the lipids appeared sensitive to significant biodegradation. Some differences in lipid reactivity were observed between the upper (3–10cm) and lower (0–3cm) sections of the cores, possibly as a result of increased exchange at the ice–water boundary for the latter. In terms of photodegradation, the phytyl side chain of chlorophyll and a tri-unsaturated highly branched isoprenoid (HBI) alkene were most affected, 24-methylenecholesterol (from diatoms) was more susceptible to photodegradation than brassicasterol (from diatoms and prymnesiophytes), while sitosterol and cholesterol, likely from a range of sources, were largely unaffected. With respect to autoxidation, the reactivity trend for the sterols was reversed, with significant autoxidation of sitosterol and cholesterol, but not of 24-methylenecholesterol or brassicasterol. The phytyl side chain of chlorophyll and a highly branched isoprenoid triene were also particularly susceptible to autoxidation. In contrast, the diatom fatty acid, C16:1, was not substantially altered by any degradation pathway. By measuring temporal changes in the proportions of specific tracers of each degradation process, we provide evidence that such abiotic reactions take place via sequential photooxidation and autoxidation, with homolytic cleavage of photochemically produced hydroperoxides leading to autoxidation of initial substrates and subsequent oxidation products. The observation of significant abiotic degradation of several lipids appears to take place despite the low temperature in sea ice (ca. 0°C) and should be considered carefully alongside other removal processes involving organic matter in marine systems.

Molecular Function of Tocopherols in Age Related Diseases

Tocopherols, with a phytyl side chain in its chroman ring, belong to vitamin E family and have several effects on organisms. They are also classified as therapeutics against different types of human diseases. Especially important roles in cell signaling and gene regulatory mechanisms make tocopherols crucial as therapeutic agents. Aging is accompanied with several degenerative disorders including cardiovascular, neuronal and metabolic diseases. The role of free radical damage in aging has been identified and tocopherols were shown to be involved in age related disorders. Recent studies and future directions will be focused in this review regarding the molecular functions of tocopherols.

Autoxidative and Photooxidative Reactivity of Highly Branched Isoprenoid (HBI) Alkenes

Autoxidation of several mono-, di-, tri- and tetra-unsaturated highly branched isoprenoid (HBI) alkenes was induced in organic solvents using a radical initiator and enhancer, and their degradation rates were compared to those of classical phytoplanktonic lipids (mono-unsaturated fatty acids, sterols and chlorophyll phytyl side-chain). Autoxidation of two HBI trienes was also investigated in senescent and highly photodegraded diatom cells, collected in the Antarctic, using Fe(2+) ions as radical inducers. Autoxidation rates of HBI alkenes were found to increase with the number of tri-substituted double bonds, as expected. Further, HBI trienes possessing one bis-allylic position (where hydrogen abstraction is highly favoured) were found to be particularly reactive towards autoxidation and degraded at similar rates compared to polyunsaturated fatty acids in diatom cells. By comparison of the autoxidation products of the most reactive tri-unsaturated HBI with the corresponding photooxidation products, some specific tracers of these two types of abiotic degradation processes were identified. The lack of reactivity of the mono-unsaturated HBI IP25 and a structurally similar di-unsaturated HBI towards autoxidative degradation supports the good preservation of these biomarkers in marine sediments.

Simplified bicyclic pyridinol analogues protect mitochondrial function

Bicyclic pyridinol antioxidants have been reported to suppress the autoxidation of methyl linoleate more effectively than α-tocopherol in benzene solution. A few novel lipophilic analogues have recently been synthesized by conjugating a pyridinol core with the phytyl side chain of α-tocopherol; these have been shown to possess potent antioxidant activity. However, the complexity of the synthetic routes has hampered their further development. Herein, we describe a facile approach, involving only five synthetic steps, to simplified analogues (1a–1c) and their acetate ester precursors (2a–2c). Simple alkyl chains of different lengths were attached to the 6-methyl group of the antioxidant core via regioselective metalation. These analogues were found to retain biological activity and exhibit protective behaviour under conditions of induced oxidative stress, which could lead to the development of more readily accessible analogues as potential antioxidants capable of preserving mitochondrial function.

Production of pristane and phytane in the marine environment: role of prokaryotes

This paper reviews studies dealing with the formation of pristane and phytane in the marine environment and focuses on the role played by prokaryotes in these processes. Prokaryotes may notably: (i) contribute to the formation of pristane during invertebrate feeding; (ii) hydrogenate isomeric pristenes and phytenes arising from degradation of the chlorophyll phytyl side-chain and/or α-tocopherol (vitamin E) to pristane and phytane, respectively; and (iii) convert trimeric oxidation products of α-tocopherol (produced abiotically in the water column and in the oxic zone of sediments) to pristane. Moreover, thermal maturation of isoprenoid components of archaea (isopranyl glyceryl ethers) also constitutes another potential source of pristane and phytane in thermally mature sediments. Prokaryotes thus appear to play a key role in formation of these isoprenoid alkanes in the marine environment.

Comparative study of UV and visible light induced degradation of lipids in non-axenic senescent cells of Emiliania huxleyi

Irradiation of killed non-axenic cells of Emiliania huxleyi (Prymnesiophyceae) by PAR and UVR resulted in a strong photodegradation of most of the unsaturated lipid components (chlorophylls, unsaturated fatty acids and brassicasterol) of this haptophyte. This degradation, which mainly involves type II (i.e. singlet oxygen-mediated) photosensitized oxidation processes, was induced by both PAR and UVR. Alkenones were the sole unsaturated components of E. huxleyi unaffected by photodegradation processes. This particular recalcitrance was attributed to the trans configuration of their double bonds, which is less reactive toward singlet oxygen than the classical cis configuration of the double bonds of the other lipids. UVR exposure also induced photosensitized stereomutation ( cis-trans isomerization) of the double bonds of some lipids (e.g. monounsaturated fatty acids and chlorophyll phytyl side-chain) and of some of their oxidation products affording (after reduction) some compounds (e.g. 9-hydroxyoctadec- cis-10-enoic and 10-hydroxyoctadec- cis-8-enoic acids arising from oleic acid oxidation and 11-hydroxyoctadec- cis-12-enoic and 12-hydroxyoctadec- cis-10-enoic acids arising from cis-vaccenic acid oxidation) sufficiently specific to act as tracers of UVR-induced photodegradation in situ. A strong photodegradation of specific bacterial monounsaturated fatty acids (e.g. cis-vaccenic and 11-MeC 18:1ω12 acids) was also observed and attributed to the migration of singlet oxygen from phytodetritus to the attached heterotrophic bacteria.

How Phenol and α-Tocopherol React with Ambient Ozone at Gas/Liquid Interfaces

The exceptional ability of alpha-tocopherol (alpha-TOH) for scavenging free radicals is believed to also underlie its protective functions in respiratory epithelia. Phenols, however, can scavenge other reactive species. Herein, we report that alpha-TOH/alpha-TO(-) reacts with closed-shell O(3)(g) on the surface of inert solvent microdroplets in < 1 ms to produce persistent alpha-TO-O(n)(-)(n = 1-4) adducts detectable by online thermospray ionization mass spectrometry. The prototype phenolate PhO(-), in contrast, undergoes electron transfer under identical conditions. These reactions are deemed to occur at the gas/liquid interface because their rates: (1) depend on pH, (2) are several orders of magnitude faster than within microdroplets saturated with O(3)(g). They also fail to incorporate solvent into the products: the same alpha-TO-O(n)(-) species are formed on acetonitrile or nucleophilic methanol microdroplets. alpha-TO-O(n = 1-3)(-) signals initially evolve with [O(3)(g)] as expected from first-generation species, but alpha-TO-O(-) reacts further with O(3)(g) and undergoes collisionally induced dissociation into a C(19)H(40) fragment (vs C(19)H(38) from alpha-TO(-)) carrying the phytyl side chain, whereas the higher alpha-TO-O(n > or = 2)(-) homologues are unreactive toward O(3)(g) and split CO(2) instead. On this basis, alpha-TO-O(-) is assigned to a chroman-6-ol (4a, 8a)-ene oxide, alpha-TO-O(2)(-) to an endoperoxide, and alpha-TO-O(3)(-) to a secondary ozonide. The atmospheric degradation of the substituted phenols detected in combustion emissions is therefore expected to produce related oxidants on the aerosol particles present in the air we breathe.

A dedicated thioesterase of the Hotdog-fold family is required for the biosynthesis of the naphthoquinone ring of vitamin K 1

Phylloquinone (vitamin K(1)) is a bipartite molecule that consists of a naphthoquinone ring attached to a phytyl side chain. The coupling of these 2 moieties depends on the hydrolysis of the CoA thioester of 1,4-dihydroxy-2-naphthoate (DHNA), which forms the naphthalenoid backbone. It is not known whether such a hydrolysis is enzymatic or chemical. In this study, comparative genomic analyses identified orthologous genes of unknown function that in most species of cyanobacteria cluster with predicted phylloquinone biosynthetic genes. The encoded approximately 16-kDa proteins display homology with some Hotdog domain-containing CoA thioesterases that are involved in the catabolism of 4-hydroxybenzoyl-CoA and gentisyl-CoA (2,5-dihydroxybenzoyl-CoA) in certain soil-dwelling bacteria. The Synechocystis ortholog, encoded by gene slr0204, was expressed as a recombinant protein and was found to form DHNA as reaction product. Unlike its homologs in the Hotdog domain family, Slr0204 showed strict substrate specificity. The Synechocystis slr0204 knockout was devoid of DHNA-CoA thioesterease activity and accumulated DHNA-CoA. As a result, knockout cells contained 13-fold less phylloquinone than their wild-type counterparts and displayed the typical photosensitivity to high light associated to phylloquinone deficiency in cyanobacteria.

Use of lipids and their degradation products as biomarkers for carbon cycling in the northwestern Mediterranean Sea

Changes in phytoplankton composition and degradation of particulate organic matter (POM) in the northwestern Mediterranean Sea were studied using time-series sediment trap samples collected during the spring of 2003 at the DYFAMED station. Lipid biomarkers (pigments, fatty acids, sterols, acyclic isoprenoids, alkenones and n-alkanols) were used to identify the main contributors to the POM produced during two phytoplankton blooms, while the effects of photooxidation, autoxidation and biodegradation were differentiated using characteristic lipid degradation products. Traps collected material corresponding to pre-bloom, bloom and post-bloom periods. Pigment analyses in the integrated (0-200 m) water column samples indicated that diatoms dominated the initial stages of the bloom event, with smaller amounts of haptophytes and pelagophytes. During the second part of bloom event there was a switch to haptophyte dominance with significant contributions from diatoms and pelagophytes, and an increased contribution from cryptophytes. Fatty acid distributions in the trap samples reflected contributions from marine bacteria, phytoplankton and zooplankton. Photooxidation and autoxidation products of monounsaturated oleic, cis-vaccenic and palmitoleic acids were detected along with photooxidation products from the chlorophyll side-chain. The relatively good correlation between the variation of U 37 K ′ index and specific phytol autoxidation product percentage allowed us to attribute the alterations of U 37 K ′ observed during the pre-bloom period and in the deeper traps to the involvement of selective autoxidative degradation processes. A variety of sterol oxidation products formed by biohydrogenation, autoxidation and photooxidation were detected. Sterol degradation products appeared to be less suited than oxidation products of monounsaturated fatty acids for the precise monitoring of the degradation state of POM, but their stable functionalized cyclic structure constitutes a useful tool to estimate the part played by biotic and abiotic processes. In these waters, biotic degradation generally predominates, but abiotic degradation is not negligible and, as expected, the extent of biotic degradation increases with depth. To obtain a more complete picture of POM degradation, the use of a pool of lipid degradation products (i.e. from unsaturated fatty acids, the phytyl side-chain and sterols) should be employed.

A possible ethanol‐catalyzed rearrangement of vitamin K1 detected by gas chromatography/mass spectrometry

We studied vitamin K(1)(20), vitamin K(1)(25), and vitamin K(1) epoxide in n-hexane and ethanol solutions by gas chromatography/mass spectrometry (GC/MS) utilizing a DB-5 MS fused-silica capillary column. In ethanol solutions of K(1), we observed an extra peak eluting from the GC column with somewhat longer retention time than K(1)(20). A similar peak following K(1)(25) was also found. These peaks were not found in n-hexane solutions of K(1). A close examination of the mass spectra of these peaks indicated that they were vitamin K(1) variants containing a base peak at m/z 225 characteristic of the methylnaphthoquinone ring with a four-carbon side chain. In addition, they contained the molecular ions of K(1)(20) and K(1)(25), respectively. We conclude that K(1)(20) and K(1)(25), but not K(1) epoxide, might undergo rearrangements in ethanol involving an intramolecular proton transfer and a shift of the beta,gamma-double bond on the phytyl side chain toward the ring. The conjugation of the phytyl double bond with the quinone ring is probably the driving force of the rearrangement. We emphasize, however, that our conclusion is based only on mass spectral analysis and would require further investigation by other spectroscopic methods.

Biosynthesis, accumulation and emission of carotenoids, α-tocopherol, plastoquinone, and isoprene in leaves under high photosynthetic irradiance

The localization of isoprenoid lipids in chloroplasts, the accumulation of particular isoprenoids under high irradiance conditions, and channelling of photosynthetically fixed carbon into plastidic thylakoid isoprenoids, volatile isoprenoids, and cytosolic sterols are reviewed. During leaf and chloroplast development in spring plastidic isoprenoid biosynthesis provides primarily thylakoid carotenoids, the phytyl side-chain of chlorophylls and the electron carriers phylloquinone K1, alpha-tocoquinone and alpha-tocopherol, as well as the nona-prenyl side-chain of plastoquinone-9. Under high irradiance, plants develop sun leaves and high light (HL) leaves with sun-type chloroplasts that possess, besides higher photosynthetic CO2 assimilation rates, different quantitative levels of pigments and prenylquinones as compared to shade leaves and low light (LL) leaves. After completion of chloroplast thylakoid synthesis plastidic isoprenoid biosynthesis continues at high irradiance conditions, constantly accumulating alpha-tocopherol (alpha-T) and the reduced form of plastoquinone-9 (PQ-9H2) deposited in the steadily enlarging osmiophilic plastoglobuli, the lipid reservoir of the chloroplast stroma. In sun leaves of beech (Fagus) and in 3-year-old sunlit Ficus leaves the level of alpha-T and PQ-9 can exceed that of chlorophyll b. Most plants respond to HL conditions (sun leaves, leaves suddenly lit by the sun) with a 1.4-2-fold increase of xanthophyll cycle carotenoids (violaxanthin, zeaxanthin, neoxanthin), an enhanced operation of the xanthophyll cycle and an increase of beta-carotene levels. This is documented by significantly lower values for the weight ratio chlorophylls to carotenoids (range: 3.6-4.6) as compared to shade and LL leaves (range: 4.8-7.0). Many plant leaves emit under HL and high temperature conditions at high rates the volatile compounds isoprene (broadleaf trees) or methylbutenol (American ponderosa pines), both of which are formed via the plastidic 1-deoxy-D: -xylulose-phosphate/2-C-methylerythritol 5-phosphate (DOXP/MEP) pathway. Other plants by contrast, accumulate particular mono- and diterpenes. Under adequate photosynthetic conditions the chloroplastidic DOXP/MEP isoprenoid pathway essentially contributes, with its C5 isoprenoid precusors, to cytosolic sterol biosynthesis. The possible cross-talk between the two cellular isoprenoid pathways, the acetate/MVA and the DOXP/MEP pathways, that preferentially proceeds in a plastid-to-cytosol direction, is shortly discussed.