Saturation-type kinetics

Furthermore, Cordes etal995 observed the saturation-type kinetics, strongly suggesting the formation of a complex between the polyelectrolyte and ester preceding bond cleavage reactions, as has been found for micellar catalysis11,1015. 

The kinetics show two regimes a low-concentration regime that is zero order in [CPOH], and a second regime at higher concentrations where the rate displays saturation-type kinetics reminiscent of Langmuir-type behavior in solid/gas systems. It suggests that the reaction takes place in the solution bulk at low concentrations of chlorophenol, while at the higher concentrations the reaction occurs predominantly at the gas bubble-liquid interface. Chlorophenols are decomposed and dechlorinated almost quantitatively to form hydroxylated aromatic intermediate products subsequently, species with fewer carbon atoms remained undetectable under these conditions. 

The kinetics of the ribozyme-catalyzed reactions were determined by measuring the initial rates of the catalyzed reaction. For reasons of solubility, anthracene-hexaethyleneglycol, and maleimidocaproic acid were used for these measurements. The initial velocities were determined by monitoring the decrease of anthracene absorbance at 365 nm over 5% conversion. The initial rate of the ribozyme-catalyzed reaction was found to be proportional to the ribozyme concentration. The reaction shows saturation-type kinetics with respect to both substrates. Catalysis was examined as a completely random bireactant system. 

The base hydrolyses of these substrates were enhanced by the addition of cationic polyelectrolyte and polysoap. Saturation type kinetics were observed and the values of rate constants for the uncatalyzed and catalyzed reactions are given as well as the values for the association constant. The results suggest that the hydrophobic interactions play a major role in the hydrolysis enhancements of the neutral and charged substrates, and that these polymeric micelles can provide both the characteristics of polyelectrolytes and micelles and thus give higher rate enchancements. 

The reaction sequence depicted in Scheme 4.4 fits both observations (second-order and saturation-type kinetics) as is evident from the following. From a kinetic viewpoint this sequence is a simple consecutive reaction with a reversible first step once the enzyme is either reduced or oxidized and the product is released the enzyme is in a different form. Due to the absence of the second substrate it cannot re-launch into the catalytic cycle. In other words this is not a catalytic reaction and the enzyme responds as a normal reactant ... 

Figure 4.27. Parameter estimation without model identification of saturation-type kinetics (enzyme and Monod kinetics) using the direct linear plot (Eisenthal and Cornish-Bowden, 1974) of r versus s or versus (a) according to Equ. 4.46. The right-side graph (b) shows the conventional plot of saturation-type kinetics, for better comprehensiveness. (Reprinted by permission from Biochem. Journal vol. 139, p. 715, copyright (c) 1974. The Biochemical Society, London.)...

For simple saturation-type kinetics, Equ. 2.54, at steady state one has... 

Figure 4.35. Plots of normalized overall reaction rate Teff/r x versus dimensionless substrate concentration s/K for different values of the modulus in case of internal transport limitation with saturation-type kinetics. (From Horvath and Engasser, 1974.)...

A combination of the concepts behind Equations (2.28) and (2.29) is applied in the activated sludge model for the kinetics of the hydrolysis processes (Henze et al., 1987). This combined concept, originally proposed by Dold et al. (1980), includes a saturation type of expression and a heterotrophic biomass with a maximum capacity for hydrolysis ... 

Equation (4) corresponds to saturation-type (Michaelis-Menten) kinetics and rate constants obtained over a suitable range of [CD], sufficient to reflect the hyperbolic curvature, can be analysed to provide the limiting rate constant, kc, and the dissociation constant, Ks (VanEtten et al., 1967a Bender and Komiyama, 1978 Szejtli, 1982 Sirlin, 1984 Tee and Takasaki, 1985). The rate constant ku is normally determined directly (at zero [CD]), and sometimes Ks can be corroborated by other means (Connors, 1987). 

The Kq saturation coefficient of oxygen in the Monod-type kinetic equation is an important parameter, too. Its value strongly influences the specific growth rate, especially when the value of oxygen concentration is of the same order of magnitude as or lower than the Kq value. Its effect is illustrated in Fig. 10 in the presence of a dispersed organic phase, e = 0.2. The increasing value of Kq (Kq was chosen to be equal to 0.64 x 10 0.16 x 10 and 0.016 x 10 kg m ) has a... 

Adsorption of FeCp-PrOH on the droplet/water interface influences the MT processes. If the MT rate of FeCp-PrOH is determined by the saturated amount of the adsorbed molecules on the interface and successive desorption to the droplet interior, the rate is given by a sum of two exponentials with the fast and slow components corresponding to the adsorption and desorption rates, respectively. Using rcc = 2 x 10 11 mol cm-2, however, the amount of FeCp-PrOH adsorbed on the droplet surface (r = 4.3 /im and C0 = 0.047 M) is calculated to be 4.6 x 10 17 mol, and this corresponds to 4.5 pC as electric charge. The calculated electric charge is 170 times smaller than the observed saturated Q t) value (750 pC), indicating that the consecutive-reaction-type kinetics cannot explain the present results. Therefore, Q(t) should be analyzed on the basis of simultaneous-reaction-type kinetics. 

In situ methods involve the external perfusion of an isolated segment of intestinal tissne." The rat has been shown to be an excellent model for human intestinal permeability." One of the principle advantages of the in situ method is that the intact rat intestinal tissne maintains a normal complement of influx and efQux transporters. Cephalosporins and beta-lactam antibiotics are known to be absorbed by oligopeptide transporters in the GI tract. The rat in situ permeability method was used to determine the saturable Michaelis-Menten-type kinetics for this class of drug molecules. In like fashion, the permeabilities of thymidine anti-viral drugs, like AZT, involving the nncleoside transporter were determined in situ. ... 

Fe concentrations measured at the start of the bioassays, and based on the estimated half-saturation constant fQ of 0.09 nM Fe (by employing MichaeHs—Menten type kinetics), the availability of Fe during that time (ambient dissolved Fe concentration of 0.03—0.04 nM) would appear to limit NO uptake by phytoplankton. These studies aU demonstrate a clear enhancement of specific and absolute NO3 uptake rates by Fe during short-term incubations, and are supported by similar results conducted in other HNLC regions including the equatorial Pacific Ocean (Coale et al., 1996 Cochlan, 2001 Price et al., 1991, 1994) and the eastern (Boyd et al., 1996, 1998 Marchetti et al., 2006) and western (Kudo et al., 2005, in review) subarctic Pacific Ocean. 

Furthermore, the initial rate of the oxidation showed a saturation at high substrate ccMicentration (Fig. 4), characteristic of Michaelis — Menten type kinetics. Using the plot of the reciprocal initial rate versus the reciprocal substrate concentration (Fig. 7), the Michaelis constant (corre nding to the dissociation constant)... 

Molybdenum and tungsten complexes as models for oxygen atom transfer enzymes have been deployed in the full catalytic cycle from Scheme 4.3 predominantly in the early days of this field of research. A selection of the respective determined Michaelis-Menten parameters were expertly reviewed by Holm et al. Since in some cases both forms of model complexes (M and M mimicking the fully reduced or fully oxidized active sites, respectively) are isolable and available in a sufficient amount, the isolated half-reactions are much more often investigated than the whole catalytic cycle. This means that either the reduced form of the enzyme model is oxidized by an oxygen donor substrate like TMAO or the oxidized form is reduced by an oxygen acceptor substrate like triphenylphosphine (PhgP). The observed kinetic behaviour is in some cases described to be of a saturation type. An observation which... 

Figure 3 presents the extent of repeated RNA transcript concentration in the preimplantation rabbit blastocyst. The kinetics of this saturation-type experiment indicate that somewhere in the neighborhood of 4%... 

Kinetic studies reveal first order dependence on both the catalyst concentration and dioxygen pressure. The dependence of the initial rate on the substrate concentration shows a saturation type behavior, indicating reversible initial coordination of the substrate to [CojLOi-OH)] (A), with subsequent coordination of Oj to the catalyst, pr ucing intermediate X, which is oxidized in the subsequent rate-determining step (Figure 48). 

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