Partial purification of a triacylglycerol lipase isolated from steelhead trout (Salmo gairdneri) adipose tissue

The substrate specificity of hormone-sensitive lipase from adipose tissue of the Antarctic fish Trematomus newnesi

Antarctic fishes of the suborder Notothenioidei characteristically possess large stores of neutral lipids that have been shown to be important both in conferring buoyant lift and as a caloric resource for energy metabolism. Previous work has established that the aerobic energy metabolism of Antarctic fish is fueled predominantly by the catabolism of fatty acids, with the catabolic machinery displaying a preference for the oxidation of unsaturated fatty acids. The composition of the fatty acids released from adipose tissue of Antarctic fish during lipolysis, however, has not previously been demonstrated. Employing a substrate competition assay, we have characterized the substrate specificity of hormone-sensitive lipase (HSL) from adipose tissue of the Antarctic fish Trematomus newnesi. Rates of oleic acid release from radiolabeled triolein were quantified in the presence and absence of a nonradiolabeled cosubstrate. Polyunsaturated species of triacylglycerols(TAGs) containing 18:2 or 20:4 depressed rates of oleate release by 70–75% below control values. Most of the molecular species of TAG containing monoenoic fatty acids (i.e. those containing 14:1, 16:1 or 20:1)had no significant effect on rates of oleate release. By contrast, oleate release from triolein was actually stimulated (by 2–4-fold) by both saturated species of TAG (i.e. those containing 14:0, 16:0 and 18:0) and those possessing long-chain (22:1 and 24:1) monoenes (by 1.2–1.5-fold). Thus,the rank order of substrate preference for adipose tissue HSL was:polyunsaturates > monoenes > saturates. Degree of fatty acid unsaturation had a more marked effect on rates of hydrolysis than did fatty acid chain length. In addition, the enzyme displayed a preference for the hydrolysis of sn-1,2 rather than sn-1,3 diacylglycerols. These data indicate that the substrate specificity of adipose tissue HSL may be an important factor in determining which fatty acids are mobilized during stimulated lipolysis and which are made available for catabolism by other tissues of Antarctic fishes. Our data further suggest that TAGs containing some saturated fatty acids may be sufficiently poor substrates for catabolism by HSL to explain their disproportionate accumulation in adipose tissue. Such a mechanism could also contribute to the ontogenetic accumulation of fats that has been reported as an underlying basis for the positive correlation of buoyancy with increasing body mass in this group.

Seasonal variation in carbohydrate and lipid metabolism of yellow perch (Perca flavescens) chronically exposed to metals in the field

The effects of heavy metals on growth, intermediary metabolism and enzyme activities were investigated in yellow perch (Perca flavescens), sampled in summer and fall from lakes situated along a contamination gradient of Cd, Zn and Cu in the mining region of Rouyn-Noranda, Québec. An exposure-dependent decrease in condition factor was observed in both seasons. Liver glycogen and triglyceride reserves were higher in summer than in fall in fish from the reference lake, while the seasonal pattern was different in fish from the contaminated lakes. Plasma free fatty acids (FFA) levels were also influenced by season and contamination. Activities of malic enzyme (ME) and glucose 6-phosphate dehydrogenase (G6PDH) in the liver were higher in the summer than in the fall in reference lakes whereas no seasonal variations were detected in fish from contaminated lakes. Activities of pyruvate kinase (PyK), aspartate transaminase (AST), phosphoenolpyruvate carboxykinase (PEPCK) and malate dehydrogenase (MDH), were higher in fish from contaminated lakes in fall but not in summer. Chronic exposure of yellow perch to sublethal levels of heavy metals impairs growth and alters the seasonal cycling of liver glycogen and triglycerides as well as the activities of metabolic enzymes.

Purification of lipases

Interest on lipases from different sources (microorganisms, animals and plants) has markedly increased in the last decade due to the potential applications of lipases in industry and in medicine. Microbial and mammalian lipases have been purified to homogeneity, allowing the successful determination of their primary aminoacid sequence and, more recently, of the three-dimensional structure. The X-ray studies of pure lipases will enable the establishment of the structure-function relationships and contribute for a better understanding of the kinetic mechanisms of lipase action on hydrolysis, synthesis and group exchange of esters. This article reviews the separation and purification techniques that were used in the recovery of microbial, mammalian and plant lipases. Several purification procedures are analysed taking into account the sequence of the methods and the number of times each method is used. Novel purification methods based on liquid-liquid extraction, membrane processes and immunopurification are also reviewed.

Purification and characterization of hepatic triacylglycerol lipase isolated from rainbow trout,Oncorhynchus mykiss

Trialcylglycerol (TG) lipase was isolated and partially purified from rainbow trout liver. Triacylglycerol lipase activity was assayed by measuring(14)C-oleic acid release from(14)C-triolein.(14)C-oleic acid release was linear for up to two hours. Optimal activity occurred at pH 7.0 and 15°C. Most of the lipase activity was recovered in the cytosolic fraction. A 27,000-fold purification was achieved after Sepharose (Bio-gel A 0.5 M, 200-400 mesh) chromatography of a resuspended 20% ammonium sulfate fraction. The molecular weight of the trout hepatic lipase as determined by size-exclusion chromatography and by SDS-polyacrylamide gel electrophoresis was 40-43 kD. Lipase-mediated hydrolysis of TG resulted in the production of diacylglycerols, monoacylglycerols, and fatty acids. Kinetic analysis indicated that Vmax=0.016 nmol/h/mg protein and that Km=0.28 mM triolein. Lipolytic activity was enhanced in the presence of cAMP/ATP-Mg(2+). These results suggest that the liver of trout possesses a neutral TG lipase that is responsible for mobilizing stored TG and is catalytically activated by phosphorylation.

Exposure to seawater stimulates lipid mobilization from depot tissues of juvenile coho (Oncorhynchus kisutch) and chinook (O. tshawytscha) salmon

Tissue lipid content and lipolytic enzyme activity was determined in selected tissues of coho salmon,Oncorhynchus kisutch, at various developmental stages (freshwater parr, freshwater smolt, seawater smolt, and seawater stunt) and in tissues of coho salmon and chinook salmon,O. tshawytscha, exposed to seawater periodically during smoltification. Among developmental groups, total lipid concentration of liver and dark muscle was highest in freshwater (FW) parr. Lipid concentration in both liver and dark muscle was significantly lower in FW smolts, seawater (SW) smolts and SW stunts; no difference was observed among these groups. Alterations in lipid composition were reflected in depot triacylglycerol lipase activity. FW smolts, SW smolts and SW stunts displayed significantly higher lipase activity than FW parr in each of the tissues examined (live, dark muscle and mesenteric fat). Early in smoltification (March, April), exposure to seawater results in enhanced lipid depletion from liver, dark muscle and mesenteric fat, both 30 and 60 days after exposure, compared to FW controls. This depletion was accompanied by increased liver (March and April) dark muscle (March) and mesenteric fat (March) lipase activity. Later in smoltification (May), salinity-induced alterations in lipid metabolism were not observed. These results indicate that exposure to seawater stimulates lipid depletion in juvenile salmon and that the depletion can be explained, in part, by increased depot lipase activity. Furthermore, these data confirm that metabolic dysfunction is associated with stunting.

Lipid dynamics in fish: aspects of absorption, transportation, deposition and mobilization

1. Aspects of lipid metabolism, including absorption and depositional processes, appear quite different in fish as compared to homeothermic vertebrates. 2. Dietary lipids in fish are absorbed as fatty acids and as triacylglycerols aggregated into chylomicra particles. 3. Interorgan transport of lipids, like that of mammals, consists of an exogenous (dietary) loop and an endogenous loop. 4. Fish store lipids among several depot organs, including mesenteric membranes, liver and muscle. 5. Several fast-acting and slow-acting agents modulate depot lipid mobilization. 6. Mobilized lipids may be transported in the serum as free fatty acids bound to specific carrier proteins.

Effects of somatostatin-25 and urotensin II on lipid and carbohydrate metabolism of coho salmon, Oncorhynchus kisutch

Salmon (Oncorhynchus kisutch) somatostatin (sSS; 4 or 8 ng/g body wt) or synthetic Gillichthys urotensin II (UII; 2 or 4 ng/g body wt) were injected intraperitoneally into juvenile freshwater coho salmon. Both sSS and UII caused a dose-dependent increase in plasma free fatty acids (FFA) which diminished with time. sSS induced an initial (1 hr) transient hyperglycemia. By contrast, UII tended to induce hypoglycemia, this effect being significant 5 hr after injection of the higher dose. Both sSS and UII depressed plasma insulin titers 1 hr after injection. By 3 hr, the sSS-associated insulin depression was no longer observed. UII treatment induced a hyperinsulinemia which was present 3 and 5 hr after peptide administration. Although no decreases in liver total lipid concentration or in mesenteric fat total tissue mass were observed, lipolytic enzyme activity within each depot was significantly enhanced by both peptides. Neither sSS nor UII altered 3H2O incorporation into fatty acids or neutral lipids. However, enhanced lipogenesis, particularly by UII, was indicated by increased NADPH production resulting from glucose-6-phosphate dehydrogenase activity. Both sSS and UII enhanced glucose mobilization, as indicated by decreased liver glycogen content and increased liver glucose-6-phosphatase activity. UII, but not sSS, stimulated glycogen synthetase activity. These results suggest that both sSS and UII stimulate hyperlipidemia by enhancing depot lipase activity and that although both factors are potentially gluconeogenetic, sSS seems to be glycogenolytic and hyperglycemic, whereas UII may channel glucose to FFA synthesis.

Both somatostatin and the caudal neuropeptide, urotensin II, stimulate lipid mobilization from coho salmon liver incubated in vitro

The direct effects of somatostatin-14 (SRIF; synthetic ovine) and the fish caudal neuropeptide, urotensin II (UII; synthetic Gillichthys), on fatty acid (FA) release and on lipolytic enzyme (triacylglycerol lipase) activity were determined on coho salmon liver slices incubated in vitro. FA release was continuously measured by pH-stat titration. Additionally, gas chromatographic analysis of the incubation medium was performed to determine the type and relative composition of medium fatty acid constituents. SRIF and UII both stimulated FA release in a dose-dependent manner; the two peptides appeared to stimulate FA release in an equimolar manner. Maximal response was obtained at 1 X 10(-5) M; ED50 was approximately 2 X 10(-7) M. SRIF-stimulated FA release did not result in differential secretion of any particular FA type. Tissue triacylglycerol lipase activity was significantly enhanced by addition of UII or SRIF (2 X 10(-6) M). Dibutyryl cAMP and IBMX both stimulated FA release and lipase activity; dbcAMP stimulated FA release in dose-dependent manner. These results indicate that SRIF and UII directly enhance lipid mobilization from salmon liver slices and suggest that SRIF- and UII-stimulated lipid mobilization from salmon liver slices is mediated through cAMP.

Changes in the rates of glycogenesis, glycogenolysis, lipogenesis, and lipolysis in selected tissues of the coho salmon (Oncorhynchus kisutch) associated with parr-smolt transformation

The rates of glycogenesis, glycogenolysis, lipogenesis and lipolysis were determined in selected tissues of the coho salmon, Oncorhynchus kisutch, during the period of parr-smolt transformation between February 1983 and June 1983. Glycogen synthesis in the liver, measured by uridine diphosphate formation, decreased 54% from initial levels. Liver glycogen phosphorylase a activity increased by 66%. Neutral lipid (sterol) and fatty acid synthesis in the liver and mesenteric fat was measured by tritium incorporation. Fatty acid synthesis in the liver and mesenteric fat decreased by 88% and 81%, respectively, between late February (parrs) and early June (smolts). There was no significant change in the rate of tritium incorporation into liver or mesenteric fat neutral lipids during the sampling period. Lipolytic rates were assessed by measuring the release of 14C-oleic acid from 14C-triolein in the presence of partially purified triacylglycerol lipase enzyme preparations from the liver, dark muscle and mesenteric fat. Liver, dark muscle and mesenteric fat lipase activity increased by 86%, 146% and 289%, respectively, during the sampling period. Increased glycogen and lipid breakdown, and concomitant decreased glycogen and fatty acid synthesis would contribute to the lipid and glycogen depletion observed in salmonid species undergoing parr-smolt transformation.