In vitro rates

It should be noted that fast inactivation of receptor signaling not only involves the desensitization of the receptor but also the components of the downstream signaling cascade. The deactivation of active Ga subunits is controlled by the intramolecular hydrolysis of bound GTP, allowing it to reform the inactive heterotrimer. Termination of G protein-mediated signaling in vivo is 10- to 100-fold faster than the in vitro rate of GTP hydrolysis by Ga subunits, suggesting... 

FIGURE 10 In vitro rates of release of progesterone from PCL films, illustrating their dependence on the film thickness and drug load. The deviation from (time)l/2 kinetics reflects the contribution of an aqueous boundary layer. The solid lines were calculated assuming an aqueous boundary layer thickness of 19 ym. (From Ref. 68.)... 

FIGURE 14 In vitro rate of release of testosterone from a PCL capsule (reservoir device), illustrating rate control by drug dissolution when the polymer membrane thickness is small. (From Ref. 68.)... 

FIGURE 21 Semilog plot of the in vitro rate of hydrolytic chain scission of various copolymers of e-caprolactone, measured under in vitro conditions. (From Ref. 95.)... 

In vivo vs. In vitro rates of desulfurization The rate of desulfurization in whole cells was reported to be limited by the rate at which the reduced flavin is provided,... 

Lee, K.-D., Nir, S. and Papahadjopoulos, D. (1993). Quantitative analysis of liposome-cell interactions in vitro rate constants of binding and endocytosis with suspension and adherent J774 cells and human monocytes, Biochemistry, 32, 889-899. 

Wolf, W. B., Bauer, L. L., Fahey, G. C. Jr. (1999). Effects of chemical modification in vitro rate and extent of food starch digestion An attempt to discover a slowly digested starch. J. FoodAgric. Chem., 47, 4178 183. 

Schlesinger et al. 20) concluded, on the basis of in vitro rates of dimerization, that the dimerization of enzyme subunits in vivo would not be as rapid as observed unless the subunits were compartmentalized in the cell. The in vitro rate of dimerization seemed to be based upon reoxidation and dimerization of reduced monomers and showed a maximum at 65 /ig/ml with respect to protein concentration. The in vivo process may be rather different, however, and later studies by Schlesinger and Barrett 21) with unreduced monomers would seem to change this conclusion because their rates did not have a maximum with respect to protein concentration. 

Similarly, the antioxidant activity of vitamin E is centreed on its chainbreaking donor activity in-vitro rate studies on a-tocopherol have shown that it is one of the most efficient alkylperoxyl radical traps, far better than commercial hindered phenols such as BHT, 2,6-di- ferf.butyl-4-methylphe-nol. Its efficiency was attributed [30, 31] to the highly stabilised structure of tocopheroxyl radical (which is formed during the rate-limiting step, reaction 3) because of favourable overlap between the p-orbitals on the two oxygen atoms. 

FIGURE 6 Summary of measurements of in situ rates of bacterial DOC consumption, calculated as the sum of bacterial production and respiration, and in vitro rates of DOC consumption, calculated from declines in DOC during batch incubations. Box-and-whisker plots show median, and upper/lower quartiles (box), and the range of values (bars). Extreme outliers are denoted by open circles. The in situ consumption rates are from the global dataset of simultaneous measurements of bacterial production and respiration collected by del Giorgio and Cole (1998), with the addition of unpublished data (see text). Because the in situ rates have been measured under a range of temperature, for this comparison the bioassay rates have not been corrected for temperature. 

In vitro rates and identity testing of all plastic components. If applicable, determine sterility and measure levels of residual ethylene oxide and its decomposition products. 

Talbot, B.G., Anderson, D.R., Harris, L.W., Yarbrough, L.W., Lermox, W.J. (1988). A comparison of in vivo and in vitro rates of aging of soman-inhibited erythrocyte AChE in different animal species. Drug Chem. Toxicol. 11(3) 289-305. 

Gerson, T., John, A., and King, A.S.D. 1985. The effects of dietary starch and fibre on the in vitro rates of lipolysis and hydrogenation by sheep rumen digesta. J. Agric. Sci. Camb. 105, 27-30. 

Hawke, J.C. and Silcock, W.R. 1970. The in vitro rates of lipolysis and biohydrogenation in rumen contents. Biochim. Biophys. Acta 218, 201-212. 

Oxidative Biotransformation in Microsomes The rapid determination of pharmacokinetic parameters, solubility, permeability, and in vitro stability in plasma or liver tissue can often provide a reasonable explanation of the mechanisms limiting oral bioavailability. An approach that is often used is to extrapolate the in vitro rate of metabolism to estimate the hepatic clearance using in vitro-in vivo correlation methods.82-86 These methods use in vitro kinetic parameters, usually Vmllx/Km or in vitro t ji, to determine the intrinsic clearance, which is then scaled to hepatic clearance using the amount of tissue in the in vitro incubation, the weight of the liver, and the well-stirred model for hepatic clearance. 

Pew (26) found digestibility of hardwoods by cellulases improved markedly by pretreatment with aqueous NaOH the effect was considerably more pronounced with hardwoods than with softwoods. Stranks (35) reported that the in vitro rate of digestion of hardwoods by rumen-inhabiting bacteria, measured by succinic acid production, was markedly increased by pretreatment with 1-5% NaOH, whereas softwoods were unaffected by the treatment. The effect of NaOH in improving the digestibility of straw has long been known (5). 

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