Lipid mobilization

Beta-1, beta-2, and beta-3 adrenergic receptors are G-protein-coupled receptors. Beta-1 and beta-2 receptors mediate the positive inotropic, chronotropic, and dro-motropic effects of the endogenous catecholamines epinephrine and norepinephrine. The beta-3 subtype seems to play a role in regulating thermogenesis and lipid mobilization in brown and white adipose tissue. Several coding and promoter polymorphisms of these receptors have been identified. Clinical studies in asthma... 

Figure 9.11 Lipid mobilization by hormone sensitive lipase (HSL)...

To detect dynamic featnres of colloidal preparations, additional methods are required. Nuclear magnetic resonance spectroscopy allows a rapid, repeatable, and noninvasive measurement of the physical parameters of lipid matrices withont sample preparation (e.g., dilution of the probe) [26,27]. Decreased lipid mobility resnlts in a remarkable broadening of the signals of lipid protons, which allows the differentiation of SLN and supercooled melts. Because of the different chemical shifts, it is possible to attribute the nuclear magnetic resonance signal to particnlar molecnles or their segments. 

Wolfe has presented an excellent description of the systematic application of stable and radioactive isotope tracers in determining the kinetics of intestinal fat absorption, hepatic triglyceride synthesis, lipid mobilization, triglyceride-fatty acid recycling, and cholesterol turnover. 

LANGMUIR TROUGH AND BALANCE LIPOPROTEIN LIPASE MICELLES LIPID ACTIVATION Lipid mobilization kinetics,... 

Lipid Increase lipid mobilization from depots Facilitate actions of lipolytic hormones... 

Feussner, I., Wastemack, C., Kindi, K., and Kuhn, H. 1995. Lipoxygenase-catalyzed oxygenation of storage lipids is implicated in lipid mobilization during germination. Proc. Natl. Acad. Sci. USA 92, 11849-11855. 

Thermally induced permeability enhancement of the more lipophilic solutes (butanol, octanol and hydrocortisone) through hairless mouse stratum corneum occurred in the temperature range also associated with lipid transitions in the calorimetry studies. Therefore, it seems likely enhanced permeabilities and lipid mobility within the stratum corneum are correlated. However, these macroscopic studies are unable to provide more specific information concerning the molecular origins of the thermal transitions. The studies provide even less information concerning possible irreversible alterations of the keratinized protein components of the stratum corneum. 

Hirai, K., Nishida, H., Shiwaku, K. Okuda, H. (1978). Studies on the plerocercoid growth factor of Spirometra erinacei (Rudolphi, 1819) with special reference to the effect on lipid mobilization in vitro. Japanese Journal of Parasitology, 27 527-33. 

The existence of adipokinetic neuropeptides was identified in locusts based upon the elevation of hemolymph lipids by CC extracts (4,5). Subsequent isolation and structural definition of Lom-AKH-I ( provided the basis for defined studies on fat body lipid mobilization using synthetic peptide. 

Lom-AKH-I suppresses fat body protein synthesis in locusts. Administration of glandular lobe extracts or synthetic Lom-AKH-I inhibits protein synthesis by 60% in immature and adult locusts (63). Lom-AKH-I does not mobilize lipids in larval locusts (36), and it is speculated that the major action of Lom-AKH-I in immatures is to regulate protein synthesis. The inhibitory effect of Lom-AKH-I on protein synthesis is observed for adult locusts in vivo at doses that are lower than those needed for lipid mobilization (64), and both arylphorin and vitellogenin synthesis are suppressed. TTie inhibitory action of Lom-AKH-I is also confirmed for in vitro protein synthesis by the muscle and gut, as well as the fat body. In preparations of dispersed fat body cells, synthetic Lom-AKH-I stimulated cAMP synthesis and lipid release but inhibited protein synthesis by 70% (38). 

Glucagon is a 29-residue polypeptide secreted by pancreas a-cells. It increases lipid mobilization and glycogenolysis to increase blood glucose levels. It was first discovered by Kimball and Murlin in 1923 (82) when studying pancreatic extracts, but the sequence was not determined until 1957 (83). 

Lipid mobilization can occur so rapidly that it exceeds the ability of the liver to oxidize the lipids or convert them into ketone bodies. The excess is reesterified and released into the blood as VLDL. 

Studies of lipid mobility have shown that the molecules close to membrane proteins are more disordered than those lipids further removed. In a lipid bilayer with variation in lateral disorder, the proteins should therefore be expected to go into positions of highest disorder. Thus, there is a driving force for proteins to locate in the "holes" in the bilayer structure, which are surroimded by maximally curved membrane. There is also a lateral packing pressure to adopt the protein according to the average hydrocarbon chain direction. Ideally, the proteins filling the "hole" of the lipid bilayer should be wedge-shaped (see Fig. 5.7). 

Oghalai JS, Zhao HB, Kutz JW, Brownell WE. 2000. Voltage-and tension-dependent lipid mobility in the outer hair cell plasma membrane. Science 287 658-661. 

Glucagon and epinephrine acutely stimulate gluconeogenesis in perfused rat liver, probably through 3, 5 -AjIP. The hormone sensitive step is apparently before the formation of three carbon intermediates, since gluconeogenesis from fructose is unaffected. 5 xhe effect of catecholamines and other hormones on lipid mobilization has been well reviewed... 

Finally, we note that a growing body of evidence shows that the stability of a planar membrane can be enhanced by spreading it across a small aperture [97], For example, a DiPhyPC bilayer suspended across a 150nm radius orifice in a glass pipet remains intact when removed from buffer [150], This suggests that it may be possible to form arrays in which fluid, stable bilayer patches are surrounded by a patterned substrate that anchors the membrane. Air stability can also be achieved by coating a PSLB with a hydrophilic polymer film (e.g., a biospecifically adsorbed protein layer [23,149]). Both of these approaches maintain some degree of lateral lipid mobility in the membrane. 

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