Lipid kinetic studies

Absorption kinetic studies on fasted rats dosed by lipid-emulsion gavage revealed rapid appearance of triehloroethylene in the blood (typieally peaking at 15 minutes post-exposure) followed by rapid disappearance (Templin et al. 1993). Rats similarly dosed with radiolabelled trichloroethylene showed rapid serum albumin adduction which peaked at 4-8 hours, then decayed with a half-life consistent with that of albumin itself (Stevens et al. 1992). However, some of the detected radioactivity may have been due to trichloroethylene metabolites rather than the parent compound. 

The lipases demonstrated very high stability in media partially or totally composed of organic solvent. In such media, the lipases catalyze esterification, transesterification, and resolution of enantiomers [19,45,75,97-100]. Nevertheless, several biphasic systems (organic-aqueous) are used for hydrolysis of lipid and fats [7,34,101]. Kinetic studies in biphase media or in inverted micelles demonstrate that the lipase behavior is different... 

A substance (1,2,3-propanetriol HOCH2CH(OH) CH2OH) that is a component and metabolite of many lipids and is commonly used in enzyme kinetic studies, serving as a cryoprotectant and stabilizing agent for pro-teins Glycerol has also been utilized as a cryosolvent in a number of cryoenzymology studies e.g., catalase. ... 

The transfer of bromine across liquid-liquid and gas-liquid interfaces is of considerable interest, for example, for sensor systems or for fundamental insights in the effects of bromine in the environment. A new methodology for kinetic studies at a lipid layer has been reported by Zhang etal. ]138]. A microelectrode immersed in the aqueous phase is placed in close distance to a lipid surface layer in contact with a gas phase. The oxidation of bromide at the electrode causes the formation of bromine, which in part escapes through the lipid layer into the gas phase (see Scheme 4). 

The kinetic studies indicated that the rate of equilibrium between large monoolein-bile salt aggregates and small monolein-bile salt aggregates was very fast. Information is needed on the rate of exchange of polar lipids between micelles since these aggregates have different structures than soap micelles, where the exchange rates are believed to be rapid (15, 21). 

B13. Barter, P. J., and Jones, M. E., Kinetic studies of the transfer of esterified cholesterol between human plasma low and high density lipoproteins. /. Lipid Res. 21, 238-249 (1980). 

In in vivo experiments, the correlation between the radioprotecting activity and antiradical properties of synthetic antioxidants was determined [14, 15]. Kinetic studies on natural antioxidants - vitamins were carried out their constants as inhibitors of radical processes were determined [16, 17]. In the works by Khrapova et al., the chemiluminescence method adapted to studies on bioantioxidants in lipids was used with this method, the problems of synergism and anthagonism of synthetic and natural antioxidants were studied and the antioxidant system in membrane lipids was characterized as a whole [18]. 

Dueker, S.R. Lin, Y. Buchholz, B.A. Schneider, P.D. Lame, M.W. Segall, H.J. Vogel, J.S. Clifford, A.J. 2000. Long-term kinetic study of P-carotene, using accelerator mass spectrometry in an adult volunteer. J. Lipid Res. 41 1790-1800. 

An assay which is based on the increase in absorption at 234 nm depends on the fact that the linoleic acid hydroperoxide formed by the action of the enzyme possesses two double bonds in a conjugated system. When arachidonic acid is used as substrate, the maximum is at 238 nm 105). The diene conjugation method, introduced by Theorell et al 91), is sensitive and convenient for kinetic studies, especially when used with a recording spectrophotometer. When preparations of low speciflc activity are used, interference from protein absorption can be a problem. In this case the lipid products can be extracted with hexane. For routine work it is convenient to use Surreys substrate mixture 106). 

We have speculated on but do not understand the mechanism causing the lytic activity of laetisaric acid. The active twelve carbon metabolite of laetisaric acid may poison a key enzyme in lipid metabolism or disrupt the integrity of the fungal cell membrane by insertion or dissolution as has been shown in Escherichia coli with sodium dodecyl sulfate and Triton X-100 (24 r 25). Why the C-12 molecule is most active remains to be determined. Kinetic studies of lipid metabolism and physicochemical and ultrastructural investigations of membranes treated with the putative active metabolite may answer these questions. 

Another milestone in the 1980s was the discovery that either water-soluble or hpid-soluble initiators with water-soluble or hpid-soluble phenolic antioxidants can be used for quantitative kinetic studies in micelles and lipid membranes . This made measurements in these systems less difficult than before when the initiators were included in high concentrations in lipid membranes due to low initiator efficiency. ... 

Kinetic studies have demonstrated that uptake of compounds into leaves is best represented by a two-compartment process a rapid distribution into the outer leaf surface, followed by a slower diffusion into the interior of the leaf. This is illustrated by studies of the uptake of DDE in spmce needles." A 10-year old spruce tree was placed in a chamber and exposed to air containing 50 ng m of DDE. It can be seen from Eigure 3.25 that DDE concentration increased more rapidly in a soluble cuticular lipid fraction than in the needle remaining after extraction. The former was obtained by extraction with dichloromethane and was considered to be representative of the lipophylic needle surface. Note that introducing the tree into the exposure chamber reduced the concentration of the DDE in the air. When the tree was transferred to a clearance chamber , DDE was lost rapidly from the extracted lipid fraction and only slowly from the remaining needle. A two-compartment model has been developed to simulate DDE uptake and release. Based on this response, if needles were to be used for monitoring, it is important to recognize that one portion of the needle reacts within hours to atmospheric concentrations, whereas the needle as a whole could take months to achieve some steady state. 

These kinetic studies suggest that it may indeed be possible to inhibit P-oxidation with minimal effect on the lipid recycling reactions in the rest of the cell. 

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