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PubMedDate not supplied

Comparative fatty acid selectivity of lipases in esterification reactions with glycerol and diol analogues in organic media.

Reaction selectivity of Pseudomonas cepacia, Rhizomucor miehei, and Candida antarctica B lipases was assessed in multicompetitive esterification reaction mixtures containing an homologous series of n-chain even carbon number fatty acid (FA; C4-C18) substrates and a single alcohol cosubstrate (glycerol, 1,2-propanediol (1,2-PD), or 1, 3-propanediol (1,3-PD)) in tert-butyl methyl ether at water activity of 0.69 or 0.90 and a reaction temperature of 35 degrees C. For P. cepacia lipase, the ordinal patterns of FA selectivities observed were, with glycerol, C8 > C10, C6, C16 > other FA; with 1,2-PD and 1, 3-PD, C16 > C8 > C14 > other FA. For R. miehei lipase, the ordinal patterns of FA selectivities observed were, with glycerol, C8 > C12 > C10, C14 > other FA; with 1,2-PD and 1,3-PD, C8 > C12 > other FA. For C. antarctica B lipase, the ordinal patterns of FA selectivities observed were, with glycerol, C8 > C10, C6, C12 > other FA; with 1, 2-PD, C8 > C10, C6 > other FA; and with 1,3-PD, C8 > C10 > C6 > other FA. The differences in selectivity among FA ranged up to 16-fold, depending upon the lipase and alcohol cosubstrate used. These findings represent intrinsic and substrate-modulated features of FA selectivities that are of particular relevance to the use of lipases for acylglycerol synthesis reactions.

Burkholderia cepacia↗
PubMedDate not supplied

Regioselective enzymatic diol esterification in batch and fixed-Bed adsorptive reactors: experiments and modeling.

The dynamic behavior of batch and fixed-bed adsorptive reactors is studied for the enzyme-catalyzed regioselective esterification of propionic acid and 2-ethyl-1,3-hexanediol in hexane. The reaction is equilibrium-limited with an apparent equilibrium constant of 0.6 +/- 0.1 at 22 degrees C. Moreover, accumulation of water produced in the reaction onto the biocatalyst causes a decrease in the catalytic activity. As a result, improvements in both reaction rate and final conversion can be achieved by operating in an adsorptive-reactor mode. Control of water in the reactor is achieved with a catalytically inert ion-exchange resin in Na-form. The resin prevents an excessive accumulation of water on the biocatalyst and reduces equilibrium limitations. The thermodynamic activity of water is identified as a key parameter for the design of such reactors. A mathematical model capable of predicting the water activity as a function of the varying concentrations of reactants and products is thus developed and found to successfully predict the experimental behavior observed in laboratory reactors. Substantial improvements in performance predicted by the model are seen experimentally in batch reactions and during the transient operation of continuous-flow fixed-bed reactors combining adsorptive and catalytic functions.

Adsorption↗
PubMedDate not supplied

Characteristics of immobilized lipase on hydrophobic superparamagnetic microspheres to catalyze esterification.

A novel immobilized lipase (from Candida rugosa) on hydrophobic and superparamagnetic microspheres was prepared and used as a biocatalyst to catalyze esterification reactions in diverse solvents and reaction systems. The results showed that the immobilized lipase had over 2-fold higher activities in higher log P value solvents. An exponential increase of lipase activity against log P of two miscible solvent mixtures was observed for the first time. Both free and immobilized lipase achieved its maximum activity at the range of water activity (a(w)) 0.5-0.8 or higher. At a(w) 0.6, the immobilized lipase exhibited markedly higher activities in heptane and a solvent-free system than did the native lipase. In multicompetitive reactions, the alcohol specificity of the lipase showed a strong chain-length dependency, and the immobilized enzyme exhibited more preference for a longer-chain alcohol, which is different from previous reports. The immobilized lipase showed higher specificities for butyric acid and the medium-chain-length fatty acids (C(8)-C(12)). Then, the immobilized lipase was extended to solvent-free synthesis of glycerides from glycerol and fatty acids. Recovered by magnetic separation, the immobilized lipase exhibited good reusability in repeated batch reaction, indicating its promising feature for biotechnology application.

Adsorption↗
PubMed2001

Improved method for determination of pectin degree of esterification by diffuse reflectance Fourier transform infrared spectroscopy.

An improved method for the determination of pectin degree of esterification (DE) by diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) was developed. Pectin samples with a range of DE as determined by gas chromatography were used for developing a calibration curve by DRIFTS. A linear relationship between the DE of pectin standards and FTIR peak ratio for ester carboxyl peak area to total carboxyl peak area was found (R(2) = 0.97). Pectin DE of various samples was calculated from the linear fit equation developed by DRIFTS. Accuracy of the DRIFTS method was determined by comparing the DE values of four commercial pectins obtained by DRIFTS methods to the values obtained by the gas chromatography method. Greater precision was obtained for the FTIR measurement of test pectin samples when the ester peak ratio was used relative to the ester peak area.

Calibration↗
PubMed2001

Steryl and stanyl esters of fatty acids by solvent-free esterification and transesterification in vacuo using lipases from Rhizomucor miehei, Candida antarctica, and Carica papaya.

Sitostanol has been converted in high to near-quantitative extent to the corresponding long-chain acyl esters via esterification with oleic acid or transesterification with methyl oleate or trioleoylglycerol using immobilized lipases from Rhizomucor miehei (Lipozyme IM) and Candida antarctica (lipase B, Novozym 435) as biocatalysts in vacuo (20-40 mbar) at 80 degrees C, whereas the conversion was markedly lower at 60 and 40 degrees C. Corresponding conversions observed with papaya (Carica papaya) latex lipase were generally lower. High conversion rates observed in transesterification of sitostanol with methyl oleate at 80 degrees C using Lipozyme IM were retained even after 10 repeated uses of the biocatalyst. Saturated sterols such as sitostanol and 5alpha-cholestan-3beta-ol were the preferred substrates as compared to Delta(5)-unsaturated cholesterol in transesterification reactions with methyl oleate using Lipozyme IM. Transesterification of cholesterol with dimethyl 1,8-octanedioate using Lipozyme IM in vacuo yielded methylcholesteryl 1,8-octanedioate (75%) and dicholesteryl 1,8-octanedioate (5%). However, transesterification of cholesterol with diethyl carbonate and that of oleyl alcohol with ethylcholesteryl carbonate, both catalyzed by Lipozyme IM, gave ethylcholesteryl carbonate and oleylcholesteryl carbonate, respectively, in low yield (20%). Moreover, cholesterol was transesterified with ethyl dihydrocinnamate using Lipozyme IM to give cholesteryl dihydrocinnamate in moderate yield (56%), whereas the corresponding reaction of lanosterol gave lanosteryl oleate in low yield (14%).

Candida↗
PubMed2006

Dialkyl 3,3'-thiodipropionate and dialkyl 2,2'-thiodiacetate antioxidants by lipase-catalyzed esterification and transesterification.

Medium- and long-chain dialkyl 3,3'-thiodipropionate antioxidants such as dioctyl 3,3'-thiodipropionate, didodecyl 3,3'-thiodipropionate, dihexadecyl 3,3'-thiodipropionate, and di-(cis-9-octadecenyl) 3,3'-thiodipropionate were prepared in high yield by lipase-catalyzed esterification and transesterification of 3,3'-thiodipropionic acid and its dimethyl ester, respectively, with the corresponding medium- or long-chain 1-alkanols, i.e., 1-octanol, 1-dodecanol, 1-hexadecanol, and cis-9-octadecen-1-ol, in vacuo (80 kPa) at moderate temperatures (60-80 degrees C) without solvents. Immobilized lipase B from Candida antarctica (Novozym 435) was the most active biocatalyst for the preparation of medium- and long-chain dialkyl 3,3'-thiodipropionates showing enzyme activities up to 1489 units/g, whereas the immobilized lipases from Rhizomucor miehei (Lipozyme RM IM) and Thermomyces lanuginosus (Lipozyme TL IM) were by far less active ( approximately 10 enzyme units/g). Maximum conversions to dialkyl 3,3'-thiodipropionates were as high as 92-98% after 4 h of reaction time. Similarly, dihexadecyl 2,2'-thiodiacetate was prepared in high yield using 2,2'-thiodiacetic acid or diethyl 2,2'-thiodiacetate and 1-hexadecanol as the starting materials and Novozym 435 as the biocatalyst.

Antioxidants↗
PubMed2006

Acidolysis reactions lead to esterification of endogenous tocopherols and compromised oxidative stability of modified oils.

For the first time, a possible mechanism responsible, in part, for the removal of endogenous antioxidants through the formation of tocopheryl esters during acidolysis reactions is proposed and confirmed. Tocopherols in the oils were found to react with carboxylic acids present in the medium, thus leading to the formation of tocopheryl esters that do not render any stability to the resultant modified oils as they lack any free hydroxyl groups on the phenolic ring of the molecule. Tocopheryl oleate, used as a standard, was synthesized through the reaction of acyl chloride of oleic acid with alpha-tocopherol (m/z 695.5 as evidenced by mass spectrometry). Subsequently, lipase-assisted esterification of alpha-, gamma-, and delta-tocopherols with oleic acid was carried out, and corresponding tocopheryl esters were isolated. In a real acidolysis reaction system involving docosahexaenoic acid single-cell oil and capric acid, high-performance liquid chromatography-mass spectrometry analysis demonstrated the presence of several tocopheryl esters. These included tocopheryl esters of myristic acid, namely, alpha-tocopheryl myristate, m/z 641.1, gamma-tocopheryl myristate, m/z 627.1, and delta-tocopheryl myristate, m/z 613.1, as well as those of palmitic acid, namely, alpha-tocopheryl palmitate, m/z 669.1, gamma-tocopheryl palmitate, m/z 655.1, and delta-tocopheryl palmitate, m/z 641.1. The mixture also contained different species of tocopheryl oleates, namely, alpha-tocopheryl oleate, m/z 695.5, gamma-tocopheryl oleate, m/z 681.1, and delta-tocopheryl oleate, m/z 667.2. Esters produced from reactions of docosahexaenoic acid and tocopherols were also detected, namely, alpha-tocopheryl docosahexaenoate, m/z 738.7, and delta-tocopheryl docosahexaenoate, m/z 710.7.

Acids↗
PubMed2000

Selectivity of Candida antarctica B lipase toward fatty acid and (Iso)propanol substrates in esterification reactions in organic media.

Fatty acid (FA) selectivity of immobilized Candida antarctica B lipase was assessed as influenced by various cosubstrate systems for ester synthesis. Reaction mixtures contained a homologous series of even-chain n-acyl donor (C(4)(-)(16)) substrates (FA or their methyl esters, FAME) and a single alcohol cosubstrate (propanol, 2-propanol, or their acetate derivatives) in hexane. Multiple FA optima were often observed, with preferences for C(6) (or C(4)) followed by C(14) and sometimes C(10). The degree of selectivity among acyl donors was modest (up to 1.28-2.60, based on ratios of selectivity constants) and was dependent on the choice of cosubstrate system. Acyl group selectivity ranged up to 1.31-1.36 for [FA + alcohol], 1. 48-2.60 for [FAME + alcohol], 1.30-1.72 for [FA + alcohol acetate], and 1.28-1.88 [FAME + alcohol acetate] reaction systems. General shifts in selectivity were observed between short-chain (C(4)(-)(8)) and long-chain (C(10)(-)(16)) FA as groups with propanol cosubstrate, whereas shifts in reaction selectivity were observed toward specific FA(s) for 2-propanol cosubstrate. Selectivity among a series of alcohol cosubstrates ranged up to 13-fold in esterification reactions with C(6) FA.

2-Propanol↗
PubMed2001

In vacuo esterification of carboxyl groups in lyophilized proteins.

A new method is described for the esterification of carboxyl groups in proteins by reaction of the lyophilized protein in vacuo with gaseous alcohol and HCI catalyst. Carboxyl groups are rapidly esterified with no protein degradation. 13C-Methyl or 13C-ethyl esters of the alpha-, gamma- and delta-carboxyl groups could be distinguished by the distinct chemical shifts of their resonances. Within the class of gamma- or delta-esters, the chemical shifts have little variation; however, the chemical shift of a C-terminal esterified alpha-carboxyl group shows a strong dependence on the nature of the C-terminal amino acid and sequence. Iodomethane reacts with deprotonated carboxyl groups in lyophilized proteins to form methyl esters, but unlike the reaction with gaseous methanol/HCI, it does not selectively methylate carboxyl groups. The procedure permits the cost-effective incorporation of isotopic labels and provides a new approach using 13C-NMR spectroscopy for determining the number of different C-termini present in a protein preparation.

Esterification↗
PubMed2004

Enzymatic esterification of lavandulol--a partial kinetic resolution of (S)-lavandulol and preparation of optically enriched (R)-lavandulyl acetate.

The asymmetric esterification of the racemic primary alcohol lavandulol was achieved using lipase B from Candida antarctica and acetic acid as acyl donor in 80% yield. The enantioselectivity of the process was characterised, and a preparative resolution of 25 mM racemic lavandulol, stopped at approx. 55% conversion, yielded (S)-lavandulol in 42% yield and 52% e.e. and (R)-lavandulyl acetate in 51% yield and 48% e.e.

Acetates↗
PubMed1986

Acinar cell carcinoma of rat pancreas: regulation of cholesterol esterification.

The regulation of cholesterol esterification during cell proliferation was studied. The serum free cholesterol, cholesterol esters and lecithin: cholesterol acyltransferase (LCAT) activity of nude mice with and without pancreatic acinar cell tumours and rats with proliferating tissues were determined. In addition, the apparent activity of acyl-CoA: cholesterol acyltransferase (ACAT) in homogenates of nude mouse tumours and proliferating rat tissues were determined and compared with those of normal nude mouse and rat tissues. Serum cholesterol ester levels were significantly lower in host nude mice with tumours and in rats with regenerating liver, and increased significantly in pregnant rats when compared with respective controls. Circulating LCAT activity levels decreased in host nude mice, in pregnant rats, and in rats with regenerating pancreas and regenerating liver. Apparent ACAT activity levels increased significantly in nude mouse tumours and in foetal and postnatal rat pancreata and also in postnatal liver. At the same time, apparent ACAT activity levels decreased in foetal and regenerating rat livers when compared with respective control tissues. These results suggest that serum cholesterol esters, circulating LCAT and cellular ACAT levels are modulated during cell proliferation.

Animals↗
PubMed2002

Immobilization, stability and esterification studies of a lipase from a Bacillus sp.

In the present paper a comparative account of the immobilization of a Bacillus lipase on different solid supports with different surface properties and their thermostability is presented. Immobilization enhanced the thermostability of lipase. At higher temperatures, lipase immobilized and cross-linked on a hydrophobic surface showed the maximum thermostability. The optimum temperature for immobilized lipase was 9 degrees C higher than for the free enzyme, while the pH optima were the same. The half-life of soluble lipase at 50 degrees C was calculated to be 4.5 h, while immobilized lipase did not lose any activity even after 8 h. The temperature stability (for 1 h) of immobilized enzyme was enhanced from 50 to 60 degrees C in comparison with non-immobilized enzyme. Applications of immobilized lipase for esterification are also presented.

Alcohol Oxidoreductases↗
PubMed1975

Palmitate activation and esterification in microsomal fractions of rat liver.

Palmitoyl-CoA synthetase activity in the microsomal fraction of rat liver was measured directly by palmitoyl-CoA production, and indirectly by converting the palmitoyl-CoA into palmitoylcarnitine under optimum conditions. Even in the latter system, palmitoyl-CoA accumulated. The rate of palmitoyl-CoA hydrolysis and the inhibition of palmitoyl-CoA synthetase by palmitoyl-CoA were each estimated to be less than 10% of the maximum rate of palmitoyl-CoA production. The concentration of palmitoyl-CoA present in the assay systems used for measuring palmitate esterification to glycerol phosphate and the activity of palmitoyl-CoA synthetase by using the carnitine-linked determination were measured. These concentrations were not altered by the addition of glycerol phosphate, or of carnitine plus carnitine palmitoyltransferase. The relationship between the activity of palmitoyl-CoA synthetase and the rate of glycerolipid synthesis was investigated. The latter activity was measured by using palmitoyl-CoA generated from palmitate, palmitoyl--AMP or palmitoylcarnitine. It is concluded that, at optimum substrate concentrations, the activity of glycerol phosphate acyltransferase is rate-limiting in the synthesis of phosphatidate by rat liver microsomal fractions. The implications of these results in the measurement of palmitoyl-CoA synthetase and in the control of glycerolipid synthesis are discussed.

Adenosine Triphosphate↗
PubMed1978

Reversal by triton WR-1339 of ethynyloestradiol-induced hepatic cholesterol esterification.

RATS TREATED WITH ETHYNYLOESTRADIOL HAVE MARKED HYPOLIPIDAEMIA: serum cholesterol is decreased to 5%, triacylglycerol to 10% and phospholipid to 70% of control concentrations. Loss of serum cholesterol follows an exponential decay, with a half-life of 1.13+/-0.09 days. After 4 days of treatment, serum cholesterol concentrations remain relatively constant (ranging from 1 to 20mg/100ml) for at least 30 days. There is a concomitant 20-fold decrease in the d<1.21 fraction of serum proteins and a similar decrease in serum apolipoproteins as measured by sodium dodecyl sulphate/10%-polyacrylamide-gel electrophoresis. The activity of hepatic microsomal acyl-CoA-cholesterol O-acetyltransferase (EC 2.3.1.26) was significantly increased by ethynyloestradiol treatment (P<0.05). This activation caused hepatic cholesteryl esters containing mainly C(18:1) fatty acids to increase linearly as serum cholesterol concentrations decreased (r=0.9675, P<0.001). Triton WR-1339, a non-ionic detergent that inhibits lipoprotein catabolism, was used to estimate hepatic lipid secretion by measuring the increment in serum lipids after its administration. At 15h after Triton WR-1339 administration, serum cholesterol concentrations were increased equally in both control and ethynyloestradiol-treated rats. In contrast, the increment of serum triacylglycerol of treated rats was 40% of that found in control rats, indicating that ethynyloestradiol inhibits hepatic triacylglycerol secretion. Triton WR-1339 inhibited the oestrogen activation of hepatic microsomal acyl-CoA-cholesterol O-acyltransferase and restored hepatic cholesteryl ester concentrations to normal values. These data suggest that ethynyloestradiol and its pharmacological ;antagonist' Triton WR-1339 alter hepatic triacylglycerol secretion via a mechanism associated with changes in hepatic cholesterol esterification.

Animals↗