Substrate constant

The proportion of Hofmann elimination is also found to increase with increasing branching in the alkyl group of the substrate (constant Y and base), and with increasing branching in the base, e.g. with (43), a bromide where preferential Saytzev elimination would normally be expected ... 

Becalski et al.98b found that the (E)/(Z) ratio of imines under rhodium-catalyzed hydrogenation conditions stayed essentially constant during the course of the reaction. This observation was explained in terms of two possibilities (1) the rates of hydrogenation of the two isomers were identical or, more likely, (2) the rate of interconversion of the two isomers was faster than the rate of hydrogenation, leaving the (E)/(Z) ratio of the substrate constant. 

The rate of a reaction and its dependency on the concentrations of the reactants can be measured in several ways. A simple method involves the measurement of the rate at zero to low conversion at different concentrations of one of the substrates, keeping the concentration of other substrates constant. The latter can be done by using an excess of the other substrates (e.g. tenfold excess), which means that we can assume that the concentrations of the latter ones are constant under so-called pseudo-first-order conditions. Secondly we can monitor the reaction rate over a longer period of time taking into account the change in concentration for this one substrate. Alternatively, one can monitor the concentrations of all species and analyse the results numerically. 

Acetylcholinesterase is subject to substrate Inhibition at high concentrations, but Mlchaells kinetics are observed at lower concentrations, because the substrate constant and the Mlchaells constant differ by a factor of 100. Turnover numbers run about 2-9 x 10 min l, and (Mlchaells constant) values are about 0.2 mM.76,116 Whatever the source, the enzyme is subject to inhibition by the same reversible and irreversible inhibitors. Most of the kinetic work has been done with the saline-extracted 11S enzyme from electric eel and the detergent-extracted 6S enzyme from erythrocytes. The former Is a tetramer derived from the native enzyme by the action of proteases the latter is a dimer. 

Second, an enzyme assay may be used to measure the kinetic properties of an enzyme such as Ku, Vmax, and inhibition characteristics. In this situation, different experimental conditions must be used. If Ku for a substrate is desired, the assay conditions must be such that the measured initial rate is first order in substrate. To determine Ku of a substrate, constant amounts of enzyme are incubated with varying amounts of substrate. A Lineweaver-Burk plot (1/v vs. 1/[S]) or direct linear plot may be used to determine Ku and V. If a reaction involves two or more substrates, each must be evalu-... 

Assay of AB-specific transhydrogenase is principally identical to that of BB-specific transhydrogenase (see Section II,C) i.e., with the natural nicotinamide nucleotides, an enzymic regenerating system is used to keep the concentration of one of the substrates constant (30, SB, 66-68, 66)... 

The selection of reaction conditions for the measurement of enzymatic activity involving two substrates is approached empirically by varying the concentration of the first substrate and keeping the concentration of the second substrate constant until maximum activity is reached. The process is then repeated with the concentration of the first substrate held at the value thus determined, while the concentration of the second substrate is varied. 

The conditions that were chosen (a full account of this phase of this research has been published in Ref. 11) for the hydrogenation reactions, using the K3[Co(CN)oH] catalyst (4.4 mmol) were 40 mL of water, 1 atm H2, repeated small (0.1 mL) injections of substrate, constant ionic strength, and reaction times never > 24 hr. The catalyst is more stable under a hydrogen atmosphere, and the problems described by others that were caused by aging reactions (12) were not encountered. 

The use of K to represent the Michaelis constant (as distinct from the dissociation and kinetic constants) as determined from the kinetic data by graphical analysis, where the biological meaning is unknown and of K, representing the true dissociation constant of the ES complex or substrate constant has been described in an earlier work (Dixon and Webb, 1958). 

Fluidic shear forces are commonly generated in vitro using cone and plate viscometers. A cone and plate viscometer (Figure 32.11a) consists of a cone that rotates in close proximity to a flat substrate. Constant shear stress is created in the region between the cone and the substrate by engineering the taper of the cone to offset the influence of the increasing tangential velocity that... 

In fed batch systems when the volumetric flow rate of the feed stream varies in a manner that maintains the concentration of the limiting substrate constant, the dilution rate must increase as time elapses because the volume occupied by the aqueous solution increases as more feed enters. Combination of equations (E) and (F) gives... 

The substrate constant (s) of methylnitrosourea is even lower than that of ethyl methanesulfonate s — 0.68). This probably accounts for the ability of the agent to induce mutation even in phages, a fact which forced Loveless to give up his idea of the uniqueness of ethylation (19666). He demonstrated (1969) that methylnitrosourea, unlike methyl methanesulfonate, alkylates guanine nucleosides at the oxygen of the C-6 position, a center which certainly has a low nucleophilicity. 

In general, a color liquid crystal display device consists of a color filter and an electrode substrate which face each other (49). A spacer is provided in the gap between the layers to keep a ceU gap between the color filter and the electrode substrate constant and uniform. As the spacer, pearls with a fixed particle diameter are dispersed. 

Description of functional enzyme inhibition by JC or IC50, whereby [5] is the substrate constant and Am the Michaelis constant [29]. 

The final constant chemical potential configuration considered represents a film of alkane melts sandwiched between two solid plates in Refs 27 and 28. The system was periodic in the x and y directions, but only a portion of the surfaces in the y direction was occupied by the solid substrate. Constant chemical potential was maintained using the reservoir method, where the liquid bubbles which form at the edge of the substrates are in equilibrium with a vapor phase which interacts across the periodic boundaries. The surfaces were modeled as static surfactant crystalline monolayers which interacted with the alkanes as united atom CH2 and CH3 groups (weakly attractive surface). Both /i-octane and 2-methylheptane systems were studied as a function of surface separation. 

Catalysis Catalyst (changing Substrate (constant Bronsted coefficient ... 

It is relatively easy to determine experimentally the Michaelis constant, A (i.e. the substrate concentration at which half-maximal reaction speed is attained), while it is not always possible to test the assumption that the turnover of [ES] is rate-determining. Hence, the distinction is now made between the substrate constant,... 

Productive binding of the substrate by the enzyme appears in the cases where the improvement of complex formation in the substrate series (decrease in the substrate constant) either increases the maximum transformation rate or has no effect on this rate. Opposite effects are observed for non-productive binding. 

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