Biosynthesis of polyamines in Euglena gracilis

In Euglena gracilis Z the biosynthesis of spermidine and spermine closely resembles the pathways occurring in mammalian tissues and in most microorganisms. l-Ornithine and not l-arginine, as is the case in most plants, is the main precursor of putrescine, and S-adenosylmethionine donates the propylamino moiety for the biosynthesis of spermidine and spermine. Cell-free extracts of Euglena synthesized sym-norspermidine and sym-norspermine from 1,3-diaminopropane and labelled S-adenosylmenthionine. The synthases for the biosynthesis of these two polyamines have a pH optimum of 7.6, like that of spermidine and spermine synthases. Ion exchange chromatography showed two peaks corresponding to the retention times of 2,4-diaminobutyric acid and 1,3-diaminopropane, lower homologues of ornithine and putrescine, respectively. Experiments with dl-2,4-diaminobutyric acid-[4-¹⁴C] did not result in significant incorporation of the label into 1,3-diaminopropane.     

The biosynthesis of long-chain hydrocarbons in the green alga Botryococcus braunii

The green colonial alga Botryococcus braunii has unusually high levels of hydrocarbons. Two distinct sites of hydrocarbon accumulation are present in the species: an internal pool present in cytoplasmic inclusions and an external pool in the trilaminar outer walls and associated globules. It is generally assumed that the hydrocarbons are produced within the cells and then excreted into the external pool to maintain the intracellular content at a normal value. Various feeding experiments showed, however, that the radioactivity of the external pool is much higher than the internal one. On the other hand, there was no decrease in the labelling of internal hydrocarbons in chase experiments. Therefore, an excretory process apparently does not take place in B. braunii. The outer wall, therefore, is the main site of hydrocarbon accumulation and also the place where the bulk of B. braunii hydrocarbons are produced. The outer wall also is involved in the matrix of colony formation and the above findings account for the sharp decrease of hydrocarbon production which is associated with the loss of colonial habit. The cultures were also shown to be unable, under usual growth conditions, to catabolize their own hydrocarbons. Such a feature, along with the extracellular location of the main site of production, may account for the abnormally high content of hydrocarbons typical of B. braunii.     

Sesquiterpene biosynthesis in maritime pine needles

The biosynthesis of sesquiterpene hydrocarbons was studied in maritime pine (Pinus pinaster) needles by incorporation of ¹⁴CO₂, [1-¹⁴C] acetate and [2-¹⁴C] mevalonate. It was shown that the mechanisms of sesquiterpene biosynthesis are different according to the applied tracer. The important role of the acyclic compound, trans-β-farnesene, before cyclisation processes is discussed.     

In vivo biosynthesis of tribromoheptene oxide in Bonnemaisonia nootkana

Experimental evidence is presented supporting the involvement of acetate and palmitate in the biosynthesis of tribromoheptene oxide in this red alga.     

The biosynthesis of phycocyanobilin in Anacystis nidulans

Aminolevulinic acid, the common precursor of linear and cyclic tetrapyrroles, can arise either by condensation of succinate and glycine or from the ent     

Phytogenesis of halomethanes: A product ofselection or a metabolic accident?

Phytoplankton (microalgae), seaweeds(macroalgae), higher plants and fungi producehalomethanes. Algae and fungi produce bothmethyl halides and polyhalomethanes, whereasplants are known to produce only methylhalides. Why these organisms producehalomethanes is a question frequently asked bychemists and biologists. This question impliesthat halomethanes have a function and have aselective value to the producing organism.Except for some fungi, the evolutionaryadvantage of producing halomethanes may notpresently exist. Polyhalomethanes areby-products of halogenation of certain organiccompounds by haloperoxidases in marine algaeand perhaps some fungi, and they may beindirectly produced in aquatic environments byalgal release of oxidized halogen species. Amain function of this enzyme is to rid the cellof harmful oxidants such as hydrogen peroxide.Monohalomethanes (methyl halides) are productsof methyltransferase activity. It has beenproposed that methyl halide production mayprovide a mechanism to regulate chloride levelsin halotolerant plants. The examination of halidecellular concentrations, halomethane productionrates, and enzyme characteristics raisesquestions about this possible function. Inalgae, plants and some fungi, methyl halidesmay be a result of the insertion of ubiquitoushalides into the active site of numerousmethyltransferases. Therefore, halomethanes maybe by-products or `accidents' of metabolism.     

Effects of salinity on synthesis of DNA,acidic polysaccharide,and ichthyotoxin in Gymnodinium breve

A Florida red tide organism, Gymnodinium breve Davis, an unarmored dinoflagellate, was grown in enriched sea water media at salinities 20–43% and constant illumination. Use of lowest (23%) and highest (43%) salinities resulted in death within 24 hr of inoculation, though good growth was obtained at all intermediate salinities (29–39%), in accord with field observation. Rates of synthesis of DNA, acidic polysaccharide and ichthyotoxin were determined as a function of salinity and growth constant (K₁₀). The relative rate of' synthesis of DNA or polysaccharide increased linearly with growth constant. Mean cell volumes, determined during log-phase growth, showed a positive correlation with doubling time. Hemolytic activity was detected in cell extracts only at high toxin concentrations (0.35–2.05 mg of ichthyotoxin). No significant difference was noted in hemolytic activity of extracts of cells grown in high (34%) or low (26%) salinity. The rate of toxin synthesis showed a linear decrease with the rate of DNA or polysaccharide synthesis.     

Fatty Acid Composition of Algae from Habitats with Varying Amounts of Illumination

The fatty acid (FA) composition of algae Ulva fenestrata (Chlorophyta), Costaria costata (Phaeophyta), and Grateloupia turuturu (Rhodophyta) differed in their illumination habitats (shaded grotto and bright light). It was found that the light intensity affect the lipid content and fatty acid (FA) ratios in the algae. In the shaded places, the content of polyunsaturated FAs of the (n-3) series in U. fenestrate and of the (n-3) and (n-6) series, except 18 : 2, in C. costata are higher than at bright light, whereas in G. turuturu, the content of 20 : 5n-3 acids in that instance was lower. The lipid content was 2.5–3.6 times higher in the algae at low light intensity. The content variation of algal lipid components apparently was related to adaptive response of these plants to illumination condition.     

赤潮藻毒素生物合成研究进展

合成毒素是赤潮藻类的一个常见特征,已知能够产生毒素的微藻有70多种。作为次级代谢产物,藻毒素的产生可能是一种压制或清除其它藻类竞争者的一种反应,在群落演替、种间竞争中发挥重要作用。目前,人们对藻毒素生物合成机理依然知之甚少,相关基因的研究仍无明显突破。利用环境因子诱导毒素生成变化进而分离差异表达基因或者比较不同产毒藻株间基因表达的差异,从中克隆藻毒素生物合成基因似乎是一种极具潜力的研究方向。     

Zur biogenese des sechsringes der hopfenbitterstoffe

The metabolisms of glucose, fructose, shikimate, phenylalanine, tyrosine and myoinositol in Humulus lupulus (hop) were studied. The results of these investigations lend support to the hypothesis, that the formation of the six membered ring of the hop bitter compounds proceeds via polyketides but not via shikimate.     

Mechanism of non-isoprenoid hydrocarbon biosynthesis in Botryococcus braunii

The green unicellular alga Botryococcus braunii shows unusually high concentrations of non-isoprenoid very long chain hydrocarbons. The structure of such hydrocarbons, the relative efficiency of various long chain fatty acids as precursors, the relationship between fatty acid and hydrocarbon concentrations (over the different physiological stages of the alga achieved during batch cultures) and the preferential localization of fatty acids lead to the conclusion that all the major non-isoprenoid hydrocarbons of B. braunii derive from the same direct precursor, oleic acid. Feeding experiments, using doubly labelled oleic acid, show that the whole carbon chain of the latter is incorporated into final hydrocarbons; accordingly such compounds do not originate from a head-to-head condensation mechanism with oleic acid acting as donor. Various features (regarding chiefly the systematic occurrence of a terminal double bond in B. braunii hydrocarbon, their close specific activities after feeding and the large inhibition in their production achieved using dithioerythritol) show that the biosynthesis of B. braunii hydrocarbons probably takes place via an elongation-decarboxylation mechanism related to that operating in some higher plants.     

两种钙藻热解产出的气态和液态烃类

在２００℃至４００℃高温和还原条件下分别对仙掌藻和乳节藻两种钙质藻类进行热模拟降解实验,分离获得气态和液态烃类化合物。随着热解温度升高,两种钙藻产烃气量明显上升,其中甲烷与乙烷气的增加最多,同时两种钙藻产出的乙烷与乙烯比值都有规律地增加,但仙掌藻产烃气量高于乳节藻。这表明钙质藻类可能是天然气的一种重要母质来源。虽然这两种钙藻随温度增加热解产出的可溶有机质及族组分的变化规律不明显,但它们的正烷烃分布特征具有相类似的变化。未经热解时它们都以Ｃ１７为主峰的低碳数正烷烃占优势;当热解温度从２００℃增加到４００℃时,它们都又表现出以Ｃ２５或Ｃ２３为主峰的较高碳数正烷烃占优势的分布特征。这与富含钙藻化石的沉积岩样品中正烷烃的分布特征相一致,说明Ｃ２５或Ｃ２３为主峰的较高碳数正烷烃占优势的分布特征可能是钙藻热解有机质的一种判识标志．     

Occurrence of a 3′-phosphoadenosine 5′-Phosphosulphate synthesizing system In two Ochromonas species

The presence of an enzyme capable of incorporating ³⁵SO₄^2? into 3′-phosphoadenosine 5′-phosphosulphate has been demonstrated,in Ochromonas danica and O. malhamensis. This system probably includes the enzymes ATP:sulphate adenyltransferase. E.C. 2.7.7.4 and ATP:adenylsulphate 3′-phosphotransferase, E.C. 2.7.1.25.