Adipose tissue albumin

Triacylglycerols must be hydrolyzed by a lipase to their constiment fatty acids and glycerol before further catab-ohsm can proceed. Much of this hydrolysis (hpolysis) occurs in adipose tissue with release of free fatty acids into the plasma, where they are found combined with semm albumin. This is followed by free fatty acid uptake into tissues (including hver, heart, kidney, muscle, lung, testis, and adipose tissue, but not readily by brain), where they are oxidized or reesterified. The uti-hzation of glycerol depends upon whether such tissues... 

Albumin/free fatty acids Adipose tissue >1.281 99 1 Free fatty acids ... 

The free fatty acids (FFA, nonesterified fatty acids, im-esterified fatty acids) arise in the plasma from hpolysis of triacylglycerol in adipose tissue or as a result of the action of hpoprotein hpase during uptake of plasma tri-acylglycerols into tissues. They are found in combination with albumin, a very effective solubilizer, in concentrations varying between 0.1 and 2.0 ieq/mL of plasma. Levels are low in the ftiUy fed condition and rise to 0.7-0.8 leq/mL in the starved state. In uncontrolled diabetes mellitus, the level may rise to as much as 2 Ieq/mL. 

The free fatty acid uptake by tissues is related directly to the plasma free fatty acid concentration, which in turn is determined by the rate of lipolysis in adipose tissue. After dissociation of the fatty acid-albumin complex at the plasma membrane, fatty acids bind to a membrane tty acid transport protein that acts as a transmembrane cotransporter with Na. On entering the cytosol, free fatty acids are bound by intracellular fatty acid-binding proteins. The role of these proteins in intracellular transport is thought to be similar to that of serum albumin in extracellular transport of long-chain fatty acids. 

Albumin and amino acid loss Muscle wasting Increased adipose tissue Fibrin formation in dialysate... 

Fatty acid utilized by muscle may arise from storage triglycerides from either adipose tissue depot or from lipid stores within the muscle itself. Lipolysis of adipose triglyceride in response to hormonal stimulation liberates free fatty acids (see Section 9.6.2) which are transported through the bloodstream to the muscle bound to albumin. Because the enzymes of fatty acid oxidation are located within subcellular organelles (peroxisomes and mitochondria), there is also need for transport of the fatty acid within the muscle cell this is achieved by fatty acid binding proteins (FABPs). Finally, the fatty acid molecules must be translocated across the mitochondrial membranes into the matrix where their catabolism occurs. To achieve this transfer, the fatty acids must first be activated by formation of a coenzyme A derivative, fatty acyl CoA, in a reaction catalysed by acyl CoA synthetase. 

Long-chain fatty acid albumin bound adipose tissue liver, skeletal muscle, kidney. 

Lipid metabolism in the liver is closely linked to the carbohydrate and amino acid metabolism. When there is a good supply of nutrients in the resorptive (wellfed) state (see p. 308), the liver converts glucose via acetyl CoA into fatty acids. The liver can also take up fatty acids from chylomicrons, which are supplied by the intestine, or from fatty acid-albumin complexes (see p. 162). Fatty acids from both sources are converted into fats and phospholipids. Together with apoproteins, they are packed into very-low-density lipoproteins (VLDLs see p.278) and then released into the blood by exocytosis. The VLDLs supply extrahepatic tissue, particularly adipose tissue and muscle. 

Chylomicrons deliver tiiacylglycerols to tissues, where lipoprotein lipase releases free fatty acids for entry into cells. Triacylglycerols stored in adipose tissue are mobilized by a hormone-sensitive triacylglycerol lipase. The released fatty acids bind to serum albumin and are carried in the blood to the heart, skeletal muscle, and other tissues that use fatty acids for fuel. 

Correct answer = C. Free fatty acids bound to albumin are increased as a result of an increased activity of hormone-sensitive lipase in adipose tissue. Hepatic ketogenesis is stimu lated by elevated levels of glucagon. The forma tion of acetyl CoA is inc reased. 

CM and VLDL secreted by intestinal cells and VLDL synthesized and secreted in the liver have similar metabolic fates. After secretion into the blood, newly formed CM and VLDL take up apoprotein (apo-C) from HDL and are subsequently removed from the blood (plasma half-life of less than 1 h in humans [137]) primarily by the action of lipoprotein lipase (LPL). Lipoprotein lipase is situated mainly in the vascular bed of the heart, skeletal muscle, and adipose tissue and catalyzes the breakdown of core TG to monoglycerides and free fatty acids, which are taken up into adjacent cells or recirculated in blood bound to albumin. The activity of LPL in the heart and skeletal muscle is inversely correlated with its activity in adipose tissue and is regulated by various hormones. Thus, in the fasted state, TG in CM and VLDL is preferentially delivered to the heart and skeletal muscle under the influence of adrenaline and glucagon, whereas in the fed state, insulin enhances LPL activity in adipose tissue, resulting in preferential uptake of TG into adipose tissue for storage as fat. 

Abbreviations BAT, brown adipose tissue BrAc, /V-bromoacetyl- BSA, bovine serum albumin CNS, central nervous system DEP, diethylpyrocarbonatc DIT, diiodotyrosine DTT, dithiothreitol G, glu-curonide Grx, glutaredoxin GSH, reduced glutathione GSSG, oxidized glutathione IRD. inner ring deiodination MIT, monoiodotyrosine ORD, outer ring deiodination PTU, propylthiouracil S, sulfate rT3, 3,3, 5 -triiodothyronine (reverse T,) Trx, thioredoxin T2, diiodothyronine T3, 3,3, 5-triiodothyronine T4, 3,3, 5,5 -tetraiodothyronine (thyroxine). 

The initial event in the utilization of fat as an energy source is the hydrolysis of triacylglycerols by lipases, an event referred to as lipolysis. The lipase of adipose tissue are activated on treatment of these cells with the hormones epinephrine, norepinephrine, glucagon, and adrenocorticotropic hormone. In adipose cells, these hormones trigger 7TM receptors that activate adenylate cyclase (Section 15,1.3 ). The increased level of cyclic AMP then stimulates protein kinase A, -which activates the lipases by phosphorylating them. Thus, epinephrine, norepinephrine, glucagon, and adrenocorticotropic hormone induce lipolysis (Figure 22.6). In contrast, insulin inhibits lipolysis. The released fatty acids are not soluble in blood plasma, and so, on release, serum albumin binds the fatty acids and serves as a carrier. By these means, free fatty acids are made accessible as a fuel in other tissues. 

Partially purified lipase from rat adipose tissue has been incubated with [ C]triolein as a substrate in sodium phosphate buffer, pH 6.8, in the presence of 1 mM NaCl and 20mg/ml of bovine serum albumin [170]. Fatty acids were isolated by adsorption on Amberlite IRA 400 in a scintillation vial, excess solvent was removed, the resin washed, and the fatty acids were displaced from the resin with NCS solubiliser and counted. 

The activity of the lipase has also been assayed with the ultramicro method of Novak [171] to determine net free fatty acid release from endogenous substrate [172]. Incubation of rat adipose tissue homogenate was carried out in 40 mM phosphate buffer, pH 6.8, in the presence of 30 mM EDTA and 2% bovine serum albumin. 

Malnutrition Albumin loss Loss of amino acids Muscle wasting Increased adipose tissue Dietary changes, parenteral nutrition, discontinue PD... 

Marasmus is a chronic condition resulting from a prolonged deficiency in total intake and/or nutrient utilization. Somatic protein (skeletal muscle) and adipose tissue (subcutaneous fat) wasting occurs, but visceral protein production (e.g., albumin and transferrin) is... 

The P-oxidation of fatty acids that occurs in the mitochondrial matrix provides the energy for gluconeogenesis in the liver. Fatty acids transported from adipose tissues by blood albumin cross the hepatic plasma membrane and... 

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