Differentiation of Gram-Negative, Nonfermentative Bacteria Isolated from Biofilters on the Basis of Fatty Acid Composition, Quinone System, and Physiological Reaction Profiles

Gram-negative, nonfermentative bacteria isolated from biofilters for off-gas treatment of animal-rendering-plant emissions were differentiated by whole-cell fatty acid analysis, quinone analysis, and numerical taxonomy based on their physiological reaction profiles. The last system consisted of 60 physiological tests and was arranged as a microtest system on microtitration plates. Based on fatty acid analyses, 31 isolates were separated into six clusters and five single-member clusters. The isolates of two clusters were identified as Alcaligenes faecalis and Pseudomonas diminuta. The remaining nine clusters were characterized by their fatty acid profiles, quinone systems, and physiological reaction profiles. Clusters resulting from fatty acid analyses were compared with those resulting from physiological reaction profiles. Six clusters could be confirmed this way. The efficiency of the physiological test system was increased by the prearrangement of the isolates according to their quinone type.     

The reaction stoichiometry between ozone and unsaturated fatty acids in an aqueous environment

The light absorption of ozone in an air stream allowed the monitoring of reactions of ozone with unsaturated fatty acids in solution. The kinetics for the reaction of ozone with linolenic acid was found to be of a pseudo-first-order after the first few minutes and did not vary with the concentration of ozone introduced into the solution. The reaction of ozone with linolenic acid in solution was found to be exceedingly rapid.When various combinations of polyunsaturated fatty acids were injected simultaneously, they reacted independently. The stoichiometry of ozone reacted to number of double bonds present in the fatty acid was one for mono- and diunsaturated; however, for triunsaturated fatty acid the stoichiometry was about 0.70.Malondialdehyde was produced upon the reaction of ozone with di- and triunsaturated fatty acids, as shown by both the thiobarbituric acid test and the characteristic UV absorption of malondialdehyde in solution. The true yield of malondialdehyde for the reaction of polyunsaturated fatty acids with ozone was found to be about 2%. In addition, other species, absorbing at 290–300 nm, were formed in solution during ozonolysis.     

The Comparative Discriminating Abilities of Lipases in Different Media and Their Application in Fatty Acid Enrichment

The generally held belief that the selectivity of lipase can be changed by changing the media from aqueous to non-aqueous was tested by monitoring the rates of hydrolysis, ester synthesis and transesterification with a range of fatty acid mono-esters. Although the absolute rates of reaction varied, hydrolysis was by far the most rapid of the three, the relative rates for the fatty acids used were similar in all three reaction types. The selectivity of the five enzymes used appeared to remain unchanged irrespective of the type of reaction, i.e. hydrolysis of p-nitrophenyl esters, direct ester synthesis with butanol and fatty acid or transesterification with butyl butyrate and fatty acid, and could not be changed by changing water activity. This principle was applied to screen for suitable lipases which could be used to increase the gamma linolenic acid content of a fatty acid mixture. Enzymes could be selected by measuring the rate of hydrolysis of a range of P-nitrophenyl esters.     

Pre-steady-state kinetics and modelling of the oxygenase and cyclooxygenase reactions of prostaglandin endoperoxide synthase

The pre-steady-state kinetics of the prostaglandin endoperoxide synthase oxygenase reaction with eicosadienoic acids and the cyclooxygenase reaction with arachidonic acid were investigated by stopped-flow spectrophotometry at 426 nm, an isosbestic point between native enzyme and compound I. A similar reaction mechanism for both types of catalysis is defined from combined kinetic experiments and numerical simulations. In the first step a fatty acid hydroperoxide reacts with the native enzyme to form compound I and the fatty acid hydroxide. In the second step the fatty acid reduces compound I to compound II and a fatty acid carbon radical is formed. This is followed by two fast steps: (1) the addition of either one molecule of oxygen (the oxygenase reaction) or two molecules of oxygen (the cyclooxygenase reaction) to the fatty acid carbon radical to form the corresponding hydroperoxyl radical, and (2) the reaction of the hydroperoxyl radical with compound II to form the fatty acid hydroperoxide and a compound I-protein radical. A unimolecular reaction of the compound I-protein radical to reform the native enzyme is assumed for the last step in the cycle. This is a slow reaction not significantly affecting steps 1 and 2 under pre-steady-state conditions. A linear dependence of the observed pseudo-first-order rate constant, k(obs), on fatty acid concentration is quantitatively reproduced by the model for both the oxygenase and cyclooxygenase reactions. The simulated second order rate constants for the conversion of native enzyme to compound I with arachidonic or eicosadienoic acids hydroperoxides as a substrate are 8 x 10(7) and 4 x 10(7) M(-1) s(-1), respectively. The simulated and experimentally obtained second-order rate constants for the conversion of compound I to compound II with arachidonic and eicosadienoic acids as a substrate are 1.2 x 10(5) and 3.0 x 10(5) M(-1) s(-1), respectively.     

Effect of acyl donor chain length and sugar/acyl donor molar ratio on enzymatic synthesis of fatty acid fructose esters

Lipase-catalyzed synthesis of fatty acid sugar esters through direct esterification was performed in 2-methyl 2-butanol as solvent. Fructose and saturated fatty acids were used as substrates and the reaction was catalyzed by immobilized Candida antarctica lipase. The effect of the initial fructose/acyl donor molar ratio and the carbon-chain length of the acyl donor as well as their reciprocal interactions on the reaction performance were investigated. For this purpose, an experimental design taking into account variations of the molar ratio (from 1:1 to 1:5) and the carbon-chain length of the fatty acid (from C8 to C18) was employed. Statistical analysis of the data indicated that the two factors as well as their interactions had significant effects on the sugar esters synthesis. The obtained results showed that whatever the molar ratio used, the highest concentration (73 g l⁻¹), fructose and fatty acid conversion yields (100% and 80%, respectively) and initial reaction rate (40 g l⁻¹ h⁻¹) were reached when using the C18 fatty acid as acyl donor. Low molar ratios gave the best fatty acid conversion yields and initial reaction rates, whereas the best total sugar ester concentrations and fructose conversion yields were obtained for high molar ratios.     

Interesterification of phosphatidylcholine with lipases in organic media

Summary Lipases were investigated with respect to their ability to catalyse the incorporation of fatty acids into phosphatidylcholine (PC) by interesterification reactions. The enzymes were dried onto solid support materials and the conversions were carried out in water-saturated toluene. Three lipases (two fungal and one plant enzyme) had the desired activity; immobilized lipase from Mucor miehei (Lipozyme) was the most active enzyme. The Lipozyme-catalysed interesterification was selective for the sn-1 position of PC and during 48 h of reaction around 50% of the fatty acids in this position were replaced with heptadecanoic acid, a fatty acid which was practically absent in the original phospholipid. Due to adsorption on the support material and the competing hydrolysis reaction the total amount of PC in the reaction solution decreased to about 40% of the original amount. Higher interesterification rates were obtained with free fatty acids as acyl donors than with fatty acid esters. Offprint requests to: I. Svensson     

Beta-ketoacyl-acyl carrier protein synthase III (FabH) is essential for bacterial fatty acid synthesis

beta-Ketoacyl-acyl carrier protein (ACP) synthase III (KAS III, also called acetoacetyl-ACP synthase) encoded by the fabH gene is thought to catalyze the first elongation reaction (Claisen condensation) of type II fatty acid synthesis in bacteria and plant plastids. However, direct in vivo evidence that KAS III catalyzes an essential reaction is lacking, because no mutant organism deficient in this activity has been isolated. We report the first bacterial strain lacking KAS III, a fabH mutant constructed in the Gram-positive bacterium Lactococcus lactis subspecies lactis IL1403. The mutant strain carries an in-frame deletion of the KAS III active site region and was isolated by gene replacement using a medium supplemented with a source of saturated and unsaturated long-chain fatty acids. The mutant strain is devoid of KAS III activity and fails to grow in the absence of supplementation with exogenous long-chain fatty acids demonstrating that KAS III plays an essential role in cellular metabolism. However, the L. lactis fabH deletion mutant requires only long-chain unsaturated fatty acids for growth, a source of long-chain saturated fatty acids is not required. Because both saturated and unsaturated fatty acids are required for growth when fatty acid synthesis is blocked by biotin starvation (which prevents the synthesis of malonyl-CoA), another pathway for saturated fatty acid synthesis must remain in the fabH deletion strain. Indeed, incorporation of [1-14C]acetate into fatty acids in vivo showed that the fabH mutant retained about 10% of the fatty acid synthetic ability of the wild-type strain and that this residual synthetic capacity was preferentially diverted to the saturated branch of the pathway. Moreover, mass spectrometry showed that the fabH mutant retained low levels of palmitic acid upon fatty acid starvation. Derivatives of the fabH deletion mutant strain were isolated that were octanoic acid auxotrophs consistent with biochemical studies indicating that the major role of FabH is production of short-chain fatty acid primers. We also confirmed the essentiality of FabH in Escherichia coli by use of a plasmid-based gene insertion/deletion system. Together these results provide the first genetic evidence demonstrating that FabH conducts the major condensation reaction in the initiation of type II fatty acid biosynthesis in both Gram-positive and Gram-negative bacteria.     

Semisynthesis and purification of homogeneous plasmenylcholine molecular species.

Methods for the efficient use of limiting amounts of fatty acid probes in the synthesis of individual molecular species of plasmenylcholine have been developed. Plasmenylcholine molecular species were synthesized through acylation of homogeneous 1-O-(Z)-hexadec-1'-enyl-sn-glycero-3-phosphocholine utilizing fatty acid anhydrides generated in situ from combined pools of reactant and recycled fatty acids by repeated addition of small amounts (10 mol%) of N,N'-dicyclohexylcarbodiimide. The efficient generation of reactive anhydrides was accomplished through minimizing irreversible formation of N-acyl urea adducts by maintaining a persistent molar excess of fatty acid (with respect to carbodiimide) during the entire reaction time course. The synthesis of multiple different sn-2 labeled plasmenylcholine probes for utilization in fluorescence, ESR, or 2H NMR spectroscopy as well as isotopically labeled plasmenylcholines for metabolic studies has been achieved in good yield (40-50% of theoretical yield based on fatty acid) by these methods. Rapid and effective purification methods utilizing high-performance liquid chromatography were developed for both large- and small-scale purifications of individual reaction mixtures which collectively resulted in the isolation of homogeneous plasmenylcholine molecular species in high yield from limiting amounts of fatty acid probes.     

Regulation of lipogenesis. Stimulation of fatty acid synthesis in vivo and in vitro in the liver of the newly hatched chick

1. A single glucose meal stimulated the incorporation of acetate into fatty acids in liver slices. If the glucose was added in vitro, it had no effect. Fructose and glycerol in vitro markedly stimulated fatty acid synthesis from acetate. Fructose and glycerol probably by-passed a rate-controlling reaction between glucose and triose phosphate. This reaction may have been stimulated by glucose administered in vivo. 2. The stimulation of fatty acid synthesis caused by fructose did not require the synthesis of enzyme, thus indicating that fatty acid-synthesizing enzymes were present in a latent form in the livers from unfed chicks.     

Stereochemistry of the acyl dihydroxyacetone phosphate acyl exchange reaction

The fatty acid of acyl dihydroxyacetone phosphate can be exchanged enzymatically for another fatty acid. It has been shown that this reaction proceeds by cleavage of the oxygen bound to C-1 of the dihydroxyacetone phosphate (DHAP) moiety rather than by the more common cleavage at the acyl to oxygen bond. In the present study, the stereochemistry of this reaction was defined further; using deuterated substrates and fast atom bombardment-mass spectrometry, it was shown that the fatty acid exchange involves the stereospecific labilization of the pro-R hydrogen at C-1 of the DHAP moiety of acyl DHAP. The mechanism of ether bond formation, in which acyl DHAP is converted to O-alkyl DHAP, also proceeds via labilization of the pro-R hydrogen and cleavage of the fatty acid at the C-1 to oxygen bond. In addition, other workers have provided evidence that the enzyme responsible for the exchange reaction is O-alkyl DHAP synthetase. Therefore, the present results support the hypothesis that the acyl exchange is the reverse reaction of the first step in O-alkyl DHAP synthesis; in both of these reactions the pro-R hydrogen of C-1 of the DHAP moiety of acyl DHAP and the fatty acid moiety are labilized with cleavage of the fatty acid at the DHAP C-1 to oxygen bond.     

Generation of fatty acids by an acyl esterase in the bioluminescent system of Photobacterium phosphoreum

The fatty acid reductase complex from Photobacterium phosphoreum has been discovered to have a long chain ester hydrolase activity associated with the 34K protein component of the complex. This protein has been resolved from the other components (50K and 58K) of the fatty acid reductase complex with a purity of greater than 95% and found to catalyze the transfer of acyl groups from acyl-CoA primarily to thiol acceptors with a low level of transfer to glycerol and water. Addition of the 50K protein of the complex caused a dramatic change in specificity increasing the transfer to oxygen acceptors. The acyl-CoA hydrolase activity increased almost 10-fold, and hence free fatty acids can be generated by the 34K protein when it is present in the fatty acid reductase complex. Hydrolysis of acyl-S-mercaptoethanol and acyl-1-glycerol and the ATP-dependent reduction of the released fatty acids to aldehyde for the luminescent reaction were also demonstrated for the reconstituted fatty acid reductase complex, raising the possibility that the immediate source of fatty acids for this reaction in vivo could be the membrane lipids and/or the fatty acid synthetase system.     

Interactions in vivo between oxidation of non-esterified fatty acids and gluconeogenesis in the newborn rat.

Metabolic interactions between fatty acid oxidation and gluconeogenesis were investigated in vivo in 16h-old newborn rats under various nutritional states. As the newborn rat has no white adipose tissue, starvation from birth induces a low rate of hepatic fatty acid oxidation. Hepatic gluconeogenesis in inhibited in the starved newborn rat when compared with the suckling rat, which receives fatty acids through the milk, at the steps catalysed by pyruvate carboxylase and glyceraldehyde 3-phosphate dehydrogenase. These inhibitions are rapidly reversed by triacylglycerol feeding. Inhibition of fatty acid oxidation by pent-4-enoate in the suckling animal mimics the effect of starvation on the pattern of hepatic gluconeogenic metabolites. It is concluded that, in the newborn rat in vivo, hepatic fatty acids oxidation can increase the gluconeogenic flux by providing the acetyl-CoA necessary for the reaction catalysed by pyruvate carboxylase and the reducing equivalents (NADH) to displace the reversible reaction catalysed by glyceraldehyde 3-phosphate dehydrogenase in the direction of gluconeogenesis.     

Lipase catalyzed production of monoacylglycerols by the esterification of fish oil fatty acids with glycerol

In this study, we attempted the efficient production of monoacylglycerols (MAG) via the lipase-catalyzed esterification of glycerol with fatty acids obtained from sardine oil. The reaction factors that influenced MAG synthesis were the glycerol to fatty acid mole ratio, amount of enzyme, organic solvent, temperature, and the type of lipase used. Porcine pancreas lipase was selected to catalyze this reaction. The optimum conditions we determined for MAG synthesis were a glycerol to fatty acid mole ratio of 1∶6, 100 mg/mL of lipase, and 30°C in dioxane. Under these conditions, the MAG content was 68% (w/w) after 72 h of reaction. The MAGs synthesized via the lipase-catalyzed esterification of glycerol with fatty acids included monomyristin, monopamiltin, and monoolein, as identified by GCMS.     

大肠杆菌3-酮基脂酰ACP还原酶110位天冬酰胺突变后的结构与功能

3-酮基脂酰ACP还原酶催化3-酮基脂酰ACP还原为3-羟基脂酰ACP,是细菌脂肪酸合成反应的关键酶之一.为了明确该酶中110位的保守天冬酰胺残基在酶催化活性和酶结构中的作用,本研究采用基因定点突变和蛋白质表达纯化技术,获得了大肠杆菌3-酮基脂酰ACP还原酶FabG的两个突变蛋白：FabG N110Q和FabG N110L.圆二色谱结果显示,天冬酰胺残基的突变改变了FabG的空间结构,使突变蛋白的α螺旋结构明显增加.以3-酮脂酰ACP为底物的酶活性测定表明,突变蛋白的酶活性均有下降,但残存的酶活性达到了FabG的75%以上.突变蛋白FabG N110Q和FabG N110L具有3-酮基脂酰ACP还原酶的活性,能在体外重建细菌脂肪酸合成反应.对fabG温度敏感突变株的遗传互补分析表明,FabG蛋白110位天冬酰胺突变为谷氨酰胺或亮氨酸后,在一定的条件下仍能互补大肠杆菌的生长.本研究结果提示,FabG 110位的天冬酰胺残基不是参与3-酮基脂酰ACP还原酶催化反应的必需氨基酸,它只是作为结构氨基酸,在维持FabG的空间结构的稳定性方面起作用.     

Biological consequences of fatty acid oxygenase reaction mechanisms

Fatty acid oxygenases catalyze the insertion of molecular oxygen into polyunsaturated fatty acids. The enzymic reactions that have been studied in detail exhibit a continuous requirement for a hydroperoxide activator and appear to proceed by a free radical chain reaction. The self-limiting nature of fatty acid oxygenase-catalyzed reactions appears to be due to enzyme self-inactivation during the reaction rather than to product inhibition. Thus “suicide” substrates are potential regulators of overall enzyme activity, although linoleate is a much weaker inactivator than the highly unsaturated fatty acids. Inhibition by added glutathione peroxidase has demonstrated the need for hydroperoxide activator in the cyclooxygenase reaction catalyzed by prostaglandin H synthase and the lipoxygenase reactions catalyzed by lung, leukocyte, and soybean enzyme preparations. The regulation of cellular hydroperoxide levels may influence the formation of prostaglandins and other autacoids by fatty acid oxygenases.     

Modification of the nutritional properties of fats using lipase catalysed directed interesterification

Summary A method for producing a monounsaturated cooking oil from beef tallow has been investigated. Immobilised lipases were used to interesterify tallow during fractional crystallisation from melted tallow, both with and without hexane present. Significant increases in the unsaturated fatty acid content of the liquid fractions were achieved by the use of upases. The water content of the enzyme beads appeared to have a large effect on reaction rates and free fatty acid formation. The presence of hexane greatly improved the efficiency of the reaction by improving the efficiency of crystal filtration.     

Synthesis of structured lipid with balanced omega-3: Omega-6 ratio by lipase-catalyzed acidolysis reaction: Optimization of reaction using response surface methodology

The present study deals with the production of structured lipid containing omega-3 and omega-6 fatty acids in the ratio of 1:1 by incorporating omega-3 fatty acids (α-linolenic acid) from linseed oil into groundnut oil using lipase (Lipozyme IM from Rhizomucor miehei) catalyzed acidolysis reaction in hexane. The reaction conditions were optimized by response surface methodology with a four-variable five-level central composite rotatable experimental design. The influence of four independent parameters, namely ratio of fatty acid concentrate from linseed to groundnut oil (0.66–1.98, w/w), reaction temperature (30–60 °C), enzyme concentration (1–5%) and reaction time (2–54 h) on omega-3 fatty acids incorporation into groundnut oil were optimized. Optimal conditions for the structured lipid containing omega-3 to omega-6 fatty acids in the ratio of 1:1 were determined to be; enzyme concentration 3.75% (w/w), temperature 37.5 °C, incubation time 30.81 h and ratio of free fatty acid concentrate from linseed oil to groundnut oil 1.16 (w/w).     

Enzymatic and Non-Enzymatic Esterification of long Polyunsaturated Fatty Acids and Lysophosphatidylcholine in Isooctane

Phosphatidylcholine containing large amounts of long polyunsaturated fatty acid, eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6), was synthesized in isooctane. Immobilized phospholipase A₂ was used as a catalyst. A parallel non-enzymatic esterification reaction was investigated in separate experiments.

The concentrations of lyso-phosphatidylcholine, polyunsaturated fatty acids, water and the enzyme were varied over wide ranges as were the temperature and the reaction time. The type of enzyme, carrier and immobilization procedure were held constant.

The yield of phosphatidylcholine was relatively high (about 21%) when the concentration of polyunsaturated fatty acids was high (300 mg/g of reaction mixture) and the water content was low (below 30% of the dry immobilized enzyme). The highest yield of phosphatidylcholine was found at 80 hours and 75°C. However, at this temperature an extensive non-enzymatic reaction between polyunsaturated fatty acids and lyso-phosphatidylcholine occurred. At 80°C the polyunsaturated fatty acids were partly oxidized. Therefore, a temperature of 45°C to 65°C is probably the optimum temperature for the reaction.     

天然脂肪酸的臭氧化—氧化分解反应

本文以棉油皂脚脂肪酸为原料,用气相色谱跟踪法研究了天然脂肪酸的臭氧化一氧化分解反应,包括溶剂的选择,脂肪酸臭氧化反应温度和时间的控制以及臭氧化物氧化分解反应温度和时间的控制等。分离反应混合物,可以获得壬二酸、C_(6～9)羧酸和棕榈酸等用途广泛的化工产品。     

Enzymatic and Non-Enzymatic Esterification of long Polyunsaturated Fatty Acids and Lysophosphatidylcholine in Isooctane

Phosphatidylcholine containing large amounts of long polyunsaturated fatty acid, eicosapentaenoic acid (C20:5) and docosahexaenoic acid (C22:6), was synthesized in isooctane. Immobilized phospholipase A₂ was used as a catalyst. A parallel non-enzymatic esterification reaction was investigated in separate experiments.

The concentrations of lyso-phosphatidylcholine, polyunsaturated fatty acids, water and the enzyme were varied over wide ranges as were the temperature and the reaction time. The type of enzyme, carrier and immobilization procedure were held constant.

The yield of phosphatidylcholine was relatively high (about 21%) when the concentration of polyunsaturated fatty acids was high (300 mg/g of reaction mixture) and the water content was low (below 30% of the dry immobilized enzyme). The highest yield of phosphatidylcholine was found at 80 hours and 75°C. However, at this temperature an extensive non-enzymatic reaction between polyunsaturated fatty acids and lyso-phosphatidylcholine occurred. At 80°C the polyunsaturated fatty acids were partly oxidized. Therefore, a temperature of 45°C to 65°C is probably the optimum temperature for the reaction.