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Rosalie Karam Salwa Karboune Richard St-Louis Selim Kermasha 《Process Biochemistry》2009,44(11):1193-1199
Lipase-catalyzed acidolysis reaction of fish liver oil with dihydroxyphenylacetic acid (DHPA) was investigated in terms of enzyme specificity as well as the effects of enzyme concentration, molar substrate ratio and organic solvent mixture on the bioconversion yield. The highest bioconversion yield of 83% was obtained when Novozym 435 was used as biocatalyst in a hexane:2-butanone mixture of 75:25 (v/v) at a fish liver oil to DHPA substrate molar ratio of 4:1; however, lower bioconversion yield (15%) was obtained when Lipozyme IM 20 was used. The bioconversion yield of phenolic monoacylglycerols (MAGs) increased from 11 to 70% when the ratio of the hexane/2-butanone reaction medium was changed from 85:15 to 75:25 (v/v), whereas that of phenolic diacylglycerols (DAGs) remained relatively unchanged (13–16%). The results also showed that the acidolysis reaction resulted in an increase of C20:5 ω-3 and C22:6 ω-3 proportions from 11.5 and 20.2% in the original fish liver oil to 22.6–27.1 and 22.8–23.1% in the phenolic lipids, respectively. The radical scavenging ability of phenolic lipids was determined to be about half-time lower than that of α-tocopherol. 相似文献
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Visual opsins bind 11-cis retinal at an orthosteric site to form rhodopsins but increasing evidence suggests that at least some are capable of binding an additional retinoid(s) at a separate, allosteric site(s). Microspectrophotometric measurements on isolated, dark-adapted, salamander photoreceptors indicated that the truncated retinal analog, β-ionone, partitioned into the membranes of green-sensitive rods; however, in blue-sensitive rod outer segments, there was an enhanced uptake of four or more β-ionones per rhodopsin. X-ray crystallography revealed binding of one β-ionone to bovine green-sensitive rod rhodopsin. Cocrystallization only succeeded with extremely high concentrations of β-ionone and binding did not alter the structure of rhodopsin from the inactive state. Salamander green-sensitive rod rhodopsin is also expected to bind β-ionone at sufficiently high concentrations because the binding site is present on its surface. Therefore, both blue- and green-sensitive rod rhodopsins have at least one allosteric binding site for retinoid, but β-ionone binds to the latter type of rhodopsin with low affinity and low efficacy. 相似文献
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Gauna C Kiewiet RM Janssen JA van de Zande B Delhanty PJ Ghigo E Hofland LJ Themmen AP van der Lely AJ 《American journal of physiology. Endocrinology and metabolism》2007,293(3):E697-E704
Acylated and unacylated ghrelin (AG and UAG) are gut hormones that exert pleiotropic actions, including regulation of insulin secretion and glucose metabolism. In this study, we investigated whether AG and UAG differentially regulate portal and systemic insulin levels after a glucose load. We studied the effects of the administration of AG (30 nmol/kg), UAG (3 and 30 nmol/kg), the ghrelin receptor antagonist [D-Lys(3)]GHRP-6 (1 micromol/kg), or various combinations of these compounds on portal and systemic levels of glucose and insulin after an intravenous glucose tolerance test (IVGTT, d-glucose 1 g/kg) in anesthetized fasted Wistar rats. UAG administration potently and dose-dependently enhanced the rise of insulin concentration induced by IVGTT in the portal and, to a lesser extent, the systemic circulation. This UAG-induced effect was completely blocked by the coadministration of exogenous AG at equimolar concentrations. Similarly to UAG, [D-Lys(3)]GHRP-6, alone or in combination with AG and UAG, strongly enhanced the portal insulin response to IVGTT, whereas exogenous AG alone did not exert any further effect. Our data demonstrate that, in glucose-stimulated conditions, exogenous UAG acts as a potent insulin secretagogue, whereas endogenous AG exerts a maximal tonic inhibition on glucose-induced insulin release. 相似文献
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Soluble guanylate cyclase (sGC) is the primary receptor for the signaling agent nitric oxide (NO). Electronic absorption and resonance Raman spectroscopy were used to show that nitrosoalkanes bind to the heme of sGC to form six-coordinate, low-spin complexes. In the sGC-nitrosopentane complex, a band assigned to an Fe-N stretching vibration is observed at 543 cm(-)(1) which is similar to values reported for other six-coordinate NO-bound hemoproteins. Nitrosoalkanes activate sGC 2-6-fold and synergize with YC-1, a synthetic benzylindazole derivative, to activate the enzyme 11-47-fold. In addition, the observed off-rates of nitrosoalkanes from sGC were found to be dependent on the alkyl chain length. A linear correlation was found between the observed off-rates and the alkyl chain length which suggests that the sGC heme has a large hydrophobic distal ligand-binding pocket. Together, these data show that nitrosoalkanes are a novel class of heme-based sGC activators and suggest that heme ligation is a general requirement for YC-1 synergism. 相似文献
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The interactions of rhodopsin and the alpha-subunit of transducin (G(t)) have been mapped using a surface modification "footprinting" approach in conjunction with mass spectrometric analysis employing a synthetic peptide corresponding to C-terminal residues 340-350 of the alpha-subunit of G(t), G(t)alpha(340-350). Membrane preparations of unactivated (Rh) and light-activated rhodopsin (Rh*), each in the presence or absence of G(t)alpha(340-350), were acetylated with the water-soluble reagent sulfosuccinimidyl acetate, and the extent of the acetylation was determined by mass spectrometry. By comparing the differences in acetylation among Rh, Rh*, and the Rh-G(t)alpha(340-350) and Rh*-G(t)alpha(340-350) complexes, we demonstrate that the surface exposure of the acetylation sites was reduced by the conformational change associated with light activation, and that binding of G(t)alpha(340-350) blocks acetylation sites on cytoplasmic loops 1, 2, and 4 of Rh*. In addition, we show evidence of interaction between the end of the C-terminal tail of rhodopsin and G(t)alpha in the unactivated state of rhodopsin. 相似文献
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Tsina E Chen C Koutalos Y Ala-Laurila P Tsacopoulos M Wiggert B Crouch RK Cornwall MC 《The Journal of general physiology》2004,124(4):429-443
The visual cycle comprises a sequence of reactions that regenerate the visual pigment in photoreceptors during dark adaptation, starting with the reduction of all-trans retinal to all-trans retinol and its clearance from photoreceptors. We have followed the reduction of retinal and clearance of retinol within bleached outer segments of red rods isolated from salamander retina by measuring its intrinsic fluorescence. Following exposure to a bright light (bleach), increasing fluorescence intensity was observed to propagate along the outer segments in a direction from the proximal region adjacent to the inner segment toward the distal tip. Peak retinol fluorescence was achieved after approximately 30 min, after which it declined very slowly. Clearance of retinol fluorescence is considerably accelerated by the presence of the exogenous lipophilic substances IRBP (interphotoreceptor retinoid binding protein) and serum albumin. We have used simultaneous fluorometric and electrophysiological measurements to compare the rate of reduction of all-trans retinal to all-trans retinol to the rate of recovery of flash response amplitude in these cells in the presence and absence of IRBP. We find that flash response recovery in rods is modestly accelerated in the presence of extracellular IRBP. These results suggest such substances may participate in the clearance of retinoids from rod photoreceptors, and that this clearance, at least in rods, may facilitate dark adaptation by accelerating the clearance of photoproducts of bleaching. 相似文献