Substrate concentration, dependence

Substrate concentration dependence of response current of the gold-black electrode was compared with that of gold disk electrode. The ferrocene-modified glucose oxidase which was used in this measurement had 11 ferrocenes per glucose oxidase. The electrode potential was controlled at 0.4 V vs. Ag/AgCl. The response current was recorded when the output reached at a steady state. The response current was enhanced when ferrocene-modified glucose oxidase was self-assembled on a porous gold-black electrode. 

How far a KM evolves relative to the substrate concentration depends on the change in structure when the substrate becomes the transition state. A limit must eventually be reached at this point, any increase in KM must be matched by a weakening of transition state binding. The problem will be most severe for large metabolites present at high concentrations. 

The substrate concentration dependence of the reaction rates was investigated kinetically to analyze the substrate binding effect. Figure 4 shows the relationships between the hydrolysis rate of amylose in the presence of the random copolymer catalyst and the concentration of the substrate at some reaction temperatures. The reaction rate clearly showed the saturation phenomenon at each reaction temperature. If the reaction proceeds via complex formation between catalyst and substrate, the elementary reaction could be described in the most simplified form as... 

The substrate concentration dependence of the cobalt carboxy-peptidase B reactions has also been studied (96). With most of the investigated substrates, the higher activity of the cobalt enzyme as compared to the zinc enzyme is essentially expressed in larger values of Vmax, while Km-values are similar. 

With the neutral [(RCN)2PdCl2] pro-catalyst system (Fig. 12.3, graph iv), computer simulation of the kinetic data acquired with various initial pro-catalyst concentrations and substrate concentrations resulted in the conclusion that the turnover rates are controlled by substrate-induced trickle feed catalyst generation, substrate concentration-dependent turnover and continuous catalyst termination. The active catalyst concentration is always low and, for a prolonged phase in the middle of the reaction, the net effect is to give rise to an apparent pseudo-zero-order kinetic profile. For both sets of data obtained with pro-catalysts of type B (Fig. 12.3), one could conceive that the kinetic product is 11, but (unlike with type A) the isomerisation to 12 is extremely rapid such that 11 does not accumulate appreciably. Of course, in this event, one needs to explain why the isomerisation of 11 now proceeds to give 12 rather than 13. With the [(phen)Pd(Me)(MeCN)]+ system, analysis of the relative concentrations of 11 and 13 as the conversion proceeds confirmed that the small amount of... 

I. Demeester, O. M, A wad, M. Bracke, and A. Lauwers. Kinetic dilution methodology for the vLKosimetric study of (he substrate concentration dependence of... 

To solve Equation 93 it is necessary to know the characteristic functions of the cellular physiology, that is, the growth rate r(m, S), the cellular division rate T(m, S), and the cell mass partition function p(m, m, S). Since these functions are substrate concentration- dependent, the substrate consumption rate must also be defined. These substrate concentration variations are calculated using the yield coefficient Yx/s, that establishes a relationship between the growth rates and the substrate consumption rate. The consumption rate is indicated by Equation 94. 

The LSV observables, the voltage sweep rate dependence (df /dlogv), the substrate concentration dependence (df /dlogCA), and the dependence of the peak potential upon the concentration of an additional reactant dlogCx) are given by eqns (60), (61) and (62), respectively. The symbols a, b,... 

The complex results observed during the reactions of AN" with phenol prompted a reinvestigation of the protonation of 9,10-diphenylanthracene radical anion (DPA ) under the same conditions (Parker, 1981J). Kinetic results summarized in Table 5 give a clear indication that this reaction is more complex than previously believed as well. In unbuffered solution, showed a definite dependence upon [DPA] indicative that Raib is greater than 1 and close to 2. In buffered solution the substrate concentration dependence was less pronounced and in the opposite direction. Similar results were obtained for the reactions of 9-phenylanthracene radical anion. 

In addition to hydroxylating xanthine and a wide range of purines, pteridines and similar compounds, xanthine oxidase is able to oxidize aromatic and aliphatic aldehydes to the corresponding carboxylic acids. Clearly then, there is a close functional as well as structural relationship between xanthine oxidase and the eukaryotic aldehyde oxidases and prokaryotic oxidoreductases. With xanthine oxidase, the pH dependence of the kinetic parameter (obtained from the substrate concentration dependence... 

Yasumori, T. Nagata, K. Yang, S. K. Chen, L.-S. Murayama, N. Yamazoe, Y Kato, R. Cytochrome P450 mediated metabolism of diazepam in human and rat involvement of human CYP2C in N-demethylation in the substrate concentration-dependent manner, Pharmacogenetics 199i, 3,291-301. 

Common solvents for direct di-rr-methane reactions are hexane, cyclohexane or acetonitrile. The substrate concentrations depend on the extinction coefficient of the substrate. 

The fluorescence-based assay described herein is used to screen large libraries of compounds, in 96-well format, for the ability to inhibit HIV protease and to accurately determine the affinity of identified inhibitors for the enzyme. Much of the discussion in this section will be widely applicable to fluorescence-based assays and enzyme assays in general. Because numerous potent inhibitors of HIV protease have been identified, part of this procedure outlines the analysis required to deal with these potent compounds. Like any enzyme assay, preparing this assay for routine use can be divided into three parts (1) determination of an appropriate enzyme concentration for assay, (2) determination of the substrate concentration dependence (Km and Vmax), and (3) determination of inhibitor concentration dependence (IC50 and K, values). Parts one and two do not need to be repeated every time inhibitor assays are run—only once to check new batches of enzyme or to troubleshoot any problems with the assay. 

The response (a decrease of viscosity) is a direct consequence of the action of the enzyme on its substrate, since the splitting of the glycosidic bonds gives a decrease in the viscosimetric average molecular weight and hydrodynamic volume of the hyaluronan chains and hence a decrease in the intrinsic and relative viscosities. With this method the rate at different concentrations cannot be compared because the initial viscosities are different and rheological measurements do not coincide. To eliminate these problems, a kinetic dilution methodology for the viscosimetric study of the substrate concentration dependence of the action of hyaluronidase was proposed [135,136]. We were able to determine the rate of reaction, expressed as the number of moles of bonds broken per unit of time, from viscosimetric data [136]. 

The fast phase of the reaction, i, is equal to the sum of all four intrinsic first-order rate constants, defining the rate of formation of E-S and the decay of E. The substrate concentration dependence of the rate is a straight line with a slope equal to and an intercept equal to i + 7 2 + k-2 - The slow phase defines the rate of decay of E-S and the rate of formation of E-X, and the rate of slow decay of E if it is noticeably biphasic. The substrate concentration dependence of the slow reaction approximates a hyperbola with an apparent defined by... 

If the rate of the conformational change is slow enough to be observed, then one must consider the complete solution to the two-step reaction sequence, with the substrate concentration dependence in rate constant ifca rather than k. Thus the time dependence of the reaction will follow a double exponential according to Eq. (13) but with the appropriate substitutions of the rate equations [Eq. (15)] to yield ... 

Figure 3. The substrate concentration dependence of sucrose or 1 -deoxy-1 -fluorosucrose hydrolysis by invertase from developing leaves of sugarbeet. Invertase activity was assayed at pH 5 by measuring glucose production as described in ref. 16.

Further validation of the mechanism proposed for the catecholase activity of the dicopper complexes [Cu2(L66)]" , [Cu2(L55)], and [Cu2(EBA)]" " (Scheme 17) has been obtained investigating the inhibitory effect of kojic acid [5-hydroxy-2-(hydroxymethyl)-y-pyrone] (154). This fungal metabolite is one of the most efficient inhibitors of mushroom tyrosinase and other polyphenol oxidases (160,161). When the catalytic oxidation of DTBCH2 was studied in the presence of kojic acid, strong competitive inhibition was observed in the steps exhibiting substrate concentration dependence,... 

Plots of kobs versus [substrate] exhibited curvature (e.g. Figure 2.10), which was attributed to a contribution from a (substrate-independent) dissociative pathway and a contribution from a (substrate and substrate concentration dependent) interchange pathway (Eqn (2.5) and Scheme 2.8). 

Fig. 4.20 Substrate concentration dependence of the catalytic rate for [Zn2(BrL2)...

Fig. 7.16 Substrate concentration dependence on the catalytic rate Iot Zn2(CH3L4)(CH3COO)2] open circle) and [Zn2(CH3L5)(CH3COO)2] (filled circle)...

Figure 7.1. Fixed substrate concentration dependence for enzymes displaying random-sequential mechanisms (a) Dependence of V ax (b) dependence of K on [A] ...

The time constant, r, of the exponential characterizing the acceleration contains a substrate concentration dependent term... 

As the interrelations between the enzyme activity and a are not linear in all cases, deviations from the activity-pH curves can be expected in the heterogeneous system as compared to homogeneous enzymology. Especially the proportion of sites working at the same external substrate concentration depends on a. Several observations and comments on these problems are cited in references [24, 40, 41, 44, 45, 52] etc. and an illustration is given in Figure 7. 

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