| 1. |
- Chen, Q, et al.
(författare)
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Desaturation and chain elongation of n - 3 and n - 6 polyunsaturated fatty acids in the human CaCo-2 cell line
- 1993
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002. ; 1166:2-3, s. 193-201
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Tidskriftsartikel (refereegranskat)abstract
- Human CaCo-2 cells were incubated with [14C]linoleic (18:2(n - 6)), [14C]linolenic (18:3(n - 3)) and [3H]eicosapentaenoic acid (20:5(n - 3)), and the interconversion of the radioactive fatty acids to higher homologues and their acylation into triacylglycerols (TG) and phospholipids were examined. An active conversion of [14C]18:3 to [14C]20:5 and [14C]docosapentaenoic acid (22:5(n - 3)) and of [3H]20:5 to [3H]22:5, but not to [3H]docosahexaenoic acid (22:6(n - 3)) was observed. In relation to the amounts that had been incorporated into cellular phospholipids and TG, the interconversion of [14C]18:3 clearly exceeded that of [14C]18:2. Addition of 10-100 microM 18:2 or 10-50 microM arachidonic acid (20:4(n - 6)) increased the percent interconversion of [14C]18:2 to [14C]20:4. E.g., addition of 50 microM 20:4 increased the formation of [14C]20:4 from 4.4 +/- 0.1% to 5.9 +/- 0.8%, decreased the incorporation into phospholipids from 64.8 +/- 6.3% to 31.4 +/- 1.2% and increased the incorporation into TG from 8.8 +/- 0.4% to 28.8 +/- 1.1%. In contrast, addition of 10-100 microM 18:3 or 20:5 significantly decreased the interconversion of both [14C]18:2 and [14C]18:3. E.g., addition of 50 microM 20:5 decreased the formation of [14C]20:4 from [14C]18:2 from 4.4 +/- 0.1% to 0.9 +/- 0.1%, whereas the effects on the acylation reactions were very similar to those of 20:4. 20:5 also decreased the formation of interconversion products from [14C]18:3. 18:2 and 20:4 caused a smaller decrease in the formation of [14C]20:5 and actually increased percent conversion to [14C]22:5. The percent conversion of [3H]20:5 to [3H]22:5 was also increased by the addition of 50-100 microM unlabeled 20:5. [14C]18:2 and [14C]18:3 were predominantly incorporated into phosphatidylcholine (PC) whereas more of the radioactive 20:4, 20:5 and 22:5 was incorporated into phosphatidylethanolamine (PE). An active fatty acid interconversion catalyzed by delta 6 and delta 5 desaturases thus occurs in the human CaCo-2 cell line, whereas conversion of 20:5(n - 3) to 22:6(n - 3) could not be demonstrated. The desaturation-elongation pathway has a preference for 18:3(n - 3) and is subjected to an efficient feedback regulation by 20:5(n - 3). Formation of 22:5 increases with available 20:5 mass and by the presence of other polyunsaturated fatty acids competing with 20:5 for acylation into phospholipids.
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| 2. |
- Chen, Qi, et al.
(författare)
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Digestion of triacylgycerols containing longchain polyenoic fatty acids in vitro by colipase dependent lipase and human milk bile salt stimulated lipase
- 1994
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002. ; 121:2, s. 239-243
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Tidskriftsartikel (refereegranskat)abstract
- To assess the role of human milk bile salt-stimulated lipase (BSSL) in the digestion of polyunsaturated ester bonds of triacylglycerols, hydrolysis of docosahexaenoic acid (22:6(n − 3)) ester bonds was compared to that of oleic acid (18:1(n − 9)) or arachidonic acid (20:4(n − 6)) esters. As model substrates, we used rat chylomicrons obtained after feeding human milk fat globules and radiolabeled fatty acids. Radiolabeled chylomicrons were incubated with colipase-dependent pancreatic lipase, with BSSL, or with both enzymes in combination. Both enzymes hydrolyzed 18:1 more efficiently than 22:6 esters. With colipase-dependent lipase there was a large accumulation of 22:6 in diacylglycerol whereas with BSSL it accumulated mainly in monoacylglycerol. Esters containing 20:4 were hydrolyzed by BSSL as efficiently as 18:1 but this fatty acid also accumulated as diacylglycerol with colipase-dependent lipase. At low bile salt concentrations, as found in duodenal contents of newborns, colipase-dependent lipase was virtually unable to hydrolyze esters of 20:4 and 22:6 whereas BSSL hydrolyzed these esters at appreciable rates. Combining the two enzymes gave the most efficient hydrolysis of all fatty acids tested regardless of bile salt concentrations. BSSL may thus have a physiological role in completing duodenal hydrolysis of milk triacylglycerols containing 22:6- or 20:4-esters to free fatty acids and monoacylglycerol.
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| 3. |
- Duan, Rui-Dong, et al.
(författare)
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Is there a specific lysophospholipase in human pancreatic juice?
- 1993
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Ingår i: Biochimica et Biophysica Acta. - : Elsevier BV. - 0006-3002. ; 1167:3, s. 326-330
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Tidskriftsartikel (refereegranskat)abstract
- The existence of a specific lysophospholipase in human pancreatic juice was evaluated. The proteins were separated by a series of chromatographic steps including Sephacryl S-200, cholate-Sepharose 4B, Sephadex G-100 and CM-Sephadex G-50. The enzyme activities against 1-palmitoyl lysolecithin (LL) as well as tributyrin (TB) and p-nitrophenyl butyrate (PNPB) were determined in all the fractions of these purification procedures. Enzyme activity against LL was always eluted in parallel with activities against TB and PNPB, and no unique activity against LL could be found. The specific activity against LL was 40-times lower than that against PNPB and 200-times lower than that against TB. It is concluded that there is no unique lysophospholipase in human pancreatic juice and that the hydrolysis of lysolecithin is most likely performed by carboxyl ester lipase.
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