Mechanisms of activation

In rats, the oxidative and reductive metaboHsm products have been identified as the 4-hydroxylated furan and [(3-cyano-l-oxopropyl)methyleneamino]-2-4-imidazohdinedione, respectively (27,42). In addition, the ease of electron transfer as a mechanism of activity with nitrofurantoin and nitrofurazone has been studied (43). 

Reserve batteries have been developed for appHcations that require a long inactive shelf period foUowed by intense discharge during which high energy and power, and sometimes operation at low ambient temperature, are required. These batteries are usually classified by the mechanism of activation which is employed. There are water-activated batteries that utilize fresh or seawater electrolyte-activated batteries, some using the complete electrolyte, some only the solvent gas-activated batteries where the gas is used as either an active cathode material or part of the electrolyte and heat-activated or thermal batteries which use a soHd salt electrolyte activated by melting on appHcation of heat. 

With regard to the anodic dissolution under film-free conditions in which the metal does not exhibit passivity, and neglecting the accompanying cathodic process, it is now generally accepted that the mechanism of active dissolution for many metals results from hydroxyl ion adsorption " , and the sequence of steps for iron are as follows ... 

In general the relevance of predictions of structure-function relationships based on molecular modeling and structural bioinformatics are threefold. First they can be used to answer the question of which partners (proteins) could interact. Second, predictions generate new hypotheses about binding site, about molecular mechanisms of activation and interaction between two partners, and can lead to new ideas for pharmacological intervention. The third aim is to use the predictions for structure-based drug design. 

Proteases (proteinases, peptidases, or proteolytic enzymes) are enzymes that break peptide bonds between amino acids of proteins. The process is called peptide cleavage, a common mechanism of activation or inactivation of enzymes. They use a molecule of water for this, and are thus classified as hydrolases. 

Activation methods can be divided into two groups. Activation by addition of selected metals (a few wt%), mainly transition metals, e.g., fine powders of Fe, Ni, Co, Cr, Pt, Pd, etc. ", or chlorides of these metals when these are reducible to the metal by hydrogen during presintering. The mechanism of activation is not understood (surface tension, surface diffusion, etc.) but is related to the electronic structure of the metal additive. Activation by carbon is also effective. Alternatively, activation utilizes powders in a specially activated state, e.g., very fine (submicronic) powders. ... 

Murakami E, Bao H, Ramesh M, McBrayer TR, Whitaker T, Micolochick Steuer HM, Schinazi RF, Stuyver LJ, Obikhod A, Otto MJ, Furman PA (2007) Mechanism of activation of beta-D-2 -deoxy-2 -fluoro-2-c-methylcytidine and inhibition of hepatitis C vims NS5B RNA polymerase. Antimicrob Agents Chemother 51 503-509... 

Mandle RJ, Kaplan A Hageman factor substrates. Human plasma prekallikrein mechanism of activation by Hageman factor and participation in Hageman factor-dependent fibrinolysis. J Biol Chem 1977 252 6097-6104. 

Kaplan A Mechanisms of activation of the classical pathway of complement by Hageman factor frag- 91 ment. J Chn Invest 1983 71 1450-1456. 

If a-hydroxylation of NPYR is its mechanism of activation, one would expect the formation of carcinogen-DNA adducts containing a 4-oxobutyl- or related residue. Adducts have been isolated from the liver RNA of NPYR treated rats, but their structures have not been determined (25). Carcinogen DNA adducts have also been isolated from cultured human esophagus, colon, and bronchus (26, 27, 28). 

Several mechanisms have been proposed to explain the activation of carbon surfaces. These have Included the removal of surface contaminants that hinder electron transfer, an Increase In surface area due to ralcro-roughenlng or bulld-up of a thin porous layer, and an Increase In the concentrations of surface functional groups that mediate electron transfer. Electrode deactivation has been correlated with an unintentional Introduction of surface contaminants (15). Improved electrode responses have been observed to follow treatments which Increase the concentration of carbon-oxygen functional groups on the surface (7-8,16). In some cases, the latter were correlated with the presence of electrochemical surface waves (16-17). However, none of the above reports discuss other possible mechanisms of activation which could be responsible for the effects observed. 

Mechanisms of active and passive transport in a family of homologous sugar transporters found in both prokaryotes and eukaryotes... 

Based on the above observation, it can conceivably be concluded that the presence of Fe-WEHS-type complexes can be of relevance to the Fe nutrition of both strategy I and strategy II plants (Fig. 1). In the case of strategy I plants, an effect on the mechanisms of active proton extrusion should also be considered (see Sect. V). 

Bonotto DM, Andrews JN (1993) The mechanism of activity ratio enhancement in karstic... 

Seger, R., Ahn, N. G., Boulton, T. G., Yanopoulos, G., Panayotatos, N., Radzziejewska, E., Ericsson, L., Bratlien, R. L., Cobb, M. H., and Krebs, E. G. (1991). Microtubule-associated protein 2 kinases, ERK1 and ERK2, undergo autophosphorylation on both tyrosine and threonine residues implications for their mechanism of activation. Proc. Natl. Acad. Sci. USASS 6142-6146. 

Receptors Linked to Ion Channels Mechanisms of Activation and Block... 

Edmonds, B., Gibb, A. J., and Colquhoun, D., Mechanisms of activation of muscle nicotinic acetylcholine receptors and the time course of endplate currents, Annu. Rev. Physiol., 57, 469-493, 1995. 

FIGURE 8.8 Mechanism of activation of protein kinase B (PKB). PI3-kinase is recruited to the membrane via direct association with the receptor PTK or via association with the docking protein Gab-1. It catalyzes the generation of phosphatidyl-3,4,5-inositolphosphate, which serves as a membrane-recruitment signal for PKB. Associated with the membrane, it is first phosphorylated in its catalytic domain by PDK1 and then by PDK2 in the hydrophobic motif. The activated PKB then detaches from the membrane. 

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