Solvent-enzyme complexes

In the earlier scheme, I represents a product formed by metabolism of the inhibitor by the enzyme. This product may be released into bulk solvent, or may interact (often covalently) with a suitably reactive component of the enzyme within the active site. This irreversibly inactivated enzyme complex is shown as El". There are two kinetic constants that can be obtained from relatively straightforward experiments with a suicide inhibitor. The Ki value is an equilibrium constant for the initial reversible step, and all the rate constants from the above scheme contribute to its value. The rate of irreversible inactivation of enzyme at a saturating concentration of the suicide inhibitor is given by fcinact. to which only k2> h, and k contribute (Silverman, 1995). At infinitely high concentrations of the inhibitor, the half-Ufe for inactivation is equal to ln2/ l inact ... 

Solvent-accessible surface representation of the GlnRS enzyme complexed with tRNA and ATP. The region of contact between tRNA and protein extends across one side of the entire enzyme surface and includes interactions from all four protein domains. The acceptor end of the tRNA and the ATP are seen in the bottom of the deep cleft. Protein is inserted between the 5 and 3 ends of the tRNA and disrupts the expected base pair between Ul and A72. (From M. G. Rould, J. J. Persona, D. Soil, and T. Steitz, Structure of E. coli glutamyl-tRNA synthetics complexed with tRNA ln and ATP at 2.8-A resolution, implications for tRNA discrimination, Science 246 1135-1142, 1989, 1989 by the AAAS.)... 

Figure 7.7. Schematic representation of a D-hydron washout perturbation. The upper panel describes the washout of deuterated D-alanine in H2O (equal starting concentrations of[ H]-D-alanine and H]-L-alanine). Upon initiation of the perturbation, H]-D-alanine-enzyme complex (lower manifold) and the H]-l-alanine-enzyme complex (upper manifold) dominate, with transient accumulation of the former, due to its slower racemization. Upon racemization of the [ H]-D-alanine-enzyme complex, the deuteron is washed out into the solvent pool. At equilibrium only the upper manifold exists, in which forward and reverse racemization rates are equivalent. The...

The solid substrates were introduced into the laccase-LD complex solutions placed in a 50 mL round bottom flasks and the mixtures were magnetically stirred at room temperature. After the end of the process the reaction products were separated and purified by the following procedure initially the mixtures were centrifuged at 2800 G force for 60 min, the clear aqueous solution of polymer-enzyme complex was filtered through 0.45 pm Whatman cellulose filter and kept at 4 C for fiirther oxidations. The yellow to brown precipitate was collected, washed twice with DI water and dried at room temperatiu e under vacuum. It was analyzed by SEC in THE. The separation of the oxidation product(s) was achieved by preparative fractionation on the same SEC system. The THE solvent in each fraction was evaporated and the dry contents were analyzed spectroscopically. The general sequence of procedures is depicted on the flow chart in Scheme 1. 

When applying EA-VTST to enzyme reactions, another kind of system/ environment separation is made. Here the reactive system is considered to be the substrate and perhaps part of the enzyme or coenzyme (and perhaps including one or two closely coupled water molecules), and the environment is the rest of the substrate-coenzyme-enzyme complex plus the (rest of the) surrounding water. In what follows we will sometimes call the reactive system the primary subsystem and the environment as the secondary subsystem. For the treatment of reactions in liquids that was presented earlier, the solvent was replaced by a homogeneous dielectric medium, which greatly simplifies the calculation. For enzyme-catalyzed reactions, we treat the environment explicitly at the atomic level of detail. 

Fatty acid synthetase (Section 26 3) Complex of enzymes that catalyzes the biosynthesis of fatty acids from acetate Field effect (Section 19 6) An electronic effect in a molecule that IS transmitted from a substituent to a reaction site via the medium (e g solvent)... 

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