Inhibition rate constants

In order to observe the chiral amplification given in Fig. 3, two considerations have to be regarded for the choice of the rate parameters (i) the rate constant ko has to be adequately small. For instance, chiral amplification does not occur if ko > 0.2 M 1 s It is apparent that if the chirally unspecific process A + Z R or S proceeds too fast it generates a high amount of racemic matter that can overwhelm the enantiospecific amplification process. (ii) The mutual inhibition rate constant k2 (R + S->-RS) must be higher than k, (R + RR, or it must occur faster than the homodimerization. Moreover, taking into account the equilibrium constants Ahetero = fe/fa and Ana,via = h/ks, it is vital that Ahetero > Aromo. i.e., the heterochiral dimer has to be thermodynamically more stable than its homochiral coun-... 

The bibenzyls 168-172 from the leaves of Glycyrrhiza glabra were tested using a new methodology which allows measuring the absolute inhibition rate constants of the oxidation process. Compounds 169 and 172 (Ainh =... 

TO and 9T0 M s, respectively) showed relatively higher inhibition rate constants [100]. Phenolics from Tragopogon porrifolius L. subsp. porrifolius showed moderate radical scavenging activity in a DHHP assay [96]. 

Antioxidant activity 842-845 practical Unlit to 899, 900 Antioxidants—see also Co-antioxidants analysis of 941, 947, 949, 955, 956, 960, 961, 981, 982 as food preservatives 982 biologicaUy active 913 calculations on 895-899 chain-breaking 840, 874 efficiency of 850-895, 900 media effects on 876-895 structural effects on 859-876 future prospects for 899-901 hydrogen atom donating abiUty of 865-867 in aircraft fuel 990 in alcohoUc beverages 973 in drinking water 963 induction period for 843 in foodstuffs 925 inhibition rate constants of 992 in Upid membranes 884-895... 

The lower part of Figure 2 deserves additional comment with regard to reaction (2). This reaction is in fact reversible and the free phosphyloxime (POX) is in itself a powerful phosphylating agent. Meanwhile, several phosphyloximes have been prepared by synthetic means (Green and Saville, 1956 Hackley Jr et al., 1959 Portmann et al., 1991 Becker et al., 1997 Leader et al., 1999). The inhibition rate constants of some phosphonyloximes can be compared with those of the parent OPs (Table 1). 

The biomolecular inhibition rate constant (ifj) describes both the affinity and the rate of cholinesterase phosphorylation and is an indicator of inhibitory potency (Kousba et al 2004 Kardos and Sultatos, 2000 Amitai et al., 1998 Carr and Chambers, 1996). A typical determination is illustrated in Fig. 10 for the in vitro inhibition of rat BuChE with chlorpyrifos-oxon. In this example, the Kj was determined by incubating BuChE with varying concentrations of ehloropyrifos-oxon (0.25-5 nAf) the maximum inhibition ranged from 10 to 90% during a 7- to 30-min incubation period (Kousba et al., 2003). The slopes obtained from this analy.sis were then analyzed by linear regression to calculate a K (Fig. lOB). Similar in vitro approaches have been used to calculate the spontaneous first-order reactivation... 

Beginning with the Ordered Uni Bi kinetic reaction scheme, Main (1964) derived a bimoleciilar inhibition rate constant, A,-, which quantiftes the inhibitory power of an OP toward AChE (the concept of ki can also be extended to BuChE). The A,- is a function of both Kp and k-> (Fig, 5) and has been considered the best estimate of inhibitory capacity of an OP (Fukuto, 1990), The larger the kj, the greater is the capacity of an individual molecule of OP to inhibit an individual molecule of enzyme. Although k, was derived based on OP interactions with AChE, the term kj can be applied with the same meaning to the inhibition of enzyme by the CMs as well (O Brien, 1968). 

Liposome (charge) pH Inhibition period, min Inhibition rate constant,... 

Inhibition rate constants calculated from plots of oxygen uptake, in M" s x 10. 6-Hydroxy-2,5,7,8-tetramethyl-2-N,N,N-trimethylethanaminiummethyl-benzenesulfonate. 

Figure 5.1. a) Increases in the concentration of inhibited enzyme as a function of time for simple irreversible enzyme inhibition, b) Semilogarithmic plot used in determination of the inhibition rate constant for the case of simple irreversible inhibition. 

Since the initial inhibitor concentration is known, the experimentally determined peudo-first-order inhibition rate constant, k (s ), can be used to... 

Figure 5.3. Initial inhibitor concentration dependence of the inhibition rate constant for time-dependent irreversible enzyme inhibition.

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