Inhibitors concentration, effect

Addition of the L-732,531 FKBP binary complex to a calcineurin activity assay resulted in increasingly nonlinear progress curves with increasing binary complex concentration. The htting of the data to Equation (6.3) revealed an inhibitor concentration effect on v-, as well as on vs and obs, consistent with a two-step mechanism of inhibition as in scheme C of Figure 6.3. Salowe and Hermes analyzed the concentration-response effects of the binary complex on v, and determined an IC50 of 0.90 pM that, after correction for I.S I/A (assuming competitive inhibition), yielded a A) value for the inhibitor encounter complex of 625 nM. 

The freezing point of the coolant should be monitored for coolants in all types of service. Additionally, maintenance of the corrosion inhibitor levels is requited of the heavy-duty service coolants and the stationary engine coolants. Because corrosion inhibitors and combinations of corrosion inhibitors work most effectively at given concentrations and specific ratios to the other inhibitors, appropriate concentrations must be maintained to maximize corrosion protection. Many manufacturers of coolants for stationary engines, and manufacturers of SCAs, provide an analytical service to monitor the effective inhibitor concentrations in the system periodically. Recommendations can then be made for proper maintenance and inhibitor replenishment. 

Change in feed composition. This may happen due to change in suppliers or due to introduction of reworked material. Unwanted effect on reaction products, by-products. Varying inhibitor concentrations in monomers from different vendors. Potential for runaway reaction. 

Table 6 Effect of Cure Inhibitor Concentration on the Charpy Notched Impact Strength (ak) at O C...

In modern practice, inhibitors are rarely used in the form of single compounds — particularly in near-neutral solutions. It is much more usual for formulations made up from two, three or more inhibitors to be employed. Three factors are responsible for this approach. Firstly, because individual inhibitors are effective with only a limited number of metals the protection of multi-metal systems requires the presence of more than one inhibitor. (Toxicity and pollution considerations frequently prevent the use of chromates as universal inhibitors.) Secondly, because of the separate advantages possessed by inhibitors of the anodic and cathodic types it is sometimes of benefit to use a formulation composed of examples from each type. This procedure often results in improved protection above that given by either type alone and makes it possible to use lower inhibitor concentrations. The third factor relates to the use of halide ions to improve the action of organic inhibitors in acid solutions. The halides are not, strictly speaking, acting as inhibitors in this sense, and their function is to assist in the adsorption of the inhibitor on to the metal surface. The second and third of these methods are often referred to as synergised treatments. 

Substrate and product inhibitions analyses involved considerations of competitive, uncompetitive, non-competitive and mixed inhibition models. The kinetic studies of the enantiomeric hydrolysis reaction in the membrane reactor included inhibition effects by substrate (ibuprofen ester) and product (2-ethoxyethanol) while varying substrate concentration (5-50 mmol-I ). The initial reaction rate obtained from experimental data was used in the primary (Hanes-Woolf plot) and secondary plots (1/Vmax versus inhibitor concentration), which gave estimates of substrate inhibition (K[s) and product inhibition constants (A jp). The inhibitor constant (K[s or K[v) is a measure of enzyme-inhibitor affinity. It is the dissociation constant of the enzyme-inhibitor complex. 

Aminotri(methylenephosphonic acid) [ATMP or AMP] is the least expensive phosphonate. It is a good, general-purpose, cost-effective scale inhibitor an effective chelant and the most thermally stable of all the common phosphonates. It is satisfactory up to at least 700 psia. However, if fed as a concentrate AIMP may easily form insoluble calcium phosphonate and it may also affect copper. ATMP has a sequestration value of 870 mg CaC03/g product at a pH level of 11 and for iron, a sequestration value of 150 mg Fe/g product at a pH level of 10. The pentasodium salt has a MW of 409. Examples include Dequest 2000/2006, Mayoquest 1230, Phos -2, Briquest 301-50A, Unihib 305, and Codex 8503. 

Effect of PG inhibitor concentration on PG activity Various amounts of inhibitor were added in the assay mixture and the degree of inhibition of polygalacturonase activity was measured which showed a linear relationship between inhibitor concentration and percent inhibition... 

Thus, by analysis of the effects of inhibitor concentration on kobs, we can obtain estimates of the affinity of the inhibitor for both the initial and final conformational states of the enzyme. 

The inhibition modality for a slow binding inhibitor is easily determined from the effects of substrate concentration on the value of k0bs at any fixed inhibitor concentration (Tian and Tsou, 1982 Copeland, 2000). For a competitive inhibitor the value of fcobs will diminish hyperbolically with increasing substrate concentration according to Equation (6.15) ... 

In Section 7.2 we presented one method for determining E T from the effects of apparent enzyme concentration on the measured value of IC50 for tight binding inhibitors. Another convenient way to determine [E T derives from the nature of Morrison s equation. When the ratio E T/A (PP equals or exceeds 200, the fractional velocity decreases very steeply with increasing inhibitor concentration, in an essen-... 

Figure 9. Effect of inhibitor concentration on wznmax f°r various inhibitors in 15% HC1 at 65 C.

These three classes of inhibition can be distinguished by virtue of the effect of variations in inhibitor concentration on the slopes and intercepts of reciprocal plots. For competitive inhibition only the slope varies. For uncompetitive inhibition only the intercept varies, while for noncompetitive inhibition both the slope and the intercept vary. 

Since competitive inhibitors have no effect on the velocity at saturating (infinite) concentrations of the substrate, the intercepts of the doublereciprocal plots (l/Vmax) al all the different inhibitor concentrations are the same. The lines at different inhibitor concentrations must all intersect... 

At very low substrate concentration ([S] approaches zero), the enzyme is mostly present as E. Since an uncompetitive inhibitor does not combine with E, the inhibitor has no effect on the velocity and no effect on Vmsa/Km (the slope of the double-reciprocal plot). In this case, termed uncompetitive, the slopes of the double-reciprocal plots are independent of inhibitor concentration and only the intercepts are affected. A series of parallel lines results when different inhibitor concentrations are used. This type of inhibition is often observed for enzymes that catalyze the reaction between two substrates. Often an inhibitor that is competitive against one of the substrates is found to give uncompetitive inhibition when the other substrate is varied. The inhibitor does combine at the active site but does not prevent the binding of one of the substrates (and vice versa). 

Noncompetitive inhibition results when the inhibitor binds to both E and ES. Here, both the slopes (Km/Vmax) and intercepts (1/Vmax) exhibit an effect of the inhibitor. The lines of different inhibitor concentration intersect (their slopes are different), but they do not intersect on the y axis (their intercepts are different). 

The effectiveness of the antioxidant action is characterized by the induction period t under fixed oxidation conditions and inhibitor concentration. Another parameter is the critical... 

DSC can be used effectively in the isothermal mode as well. In this case, the container with the sample is inserted into the DSC preheated to the desired test temperature. This type of experiment should be performed to examine systems for induction periods that occur with autocatalytic reactions and with inhibitor depletion reactions. (Reactions with induction periods can give misleading results in the DSC operated with increasing temperature scans.) Autocatalytic reactions are those whose rates are proportional to the concentration of one or more of the reaction products. Some hydroperoxides and peroxy esters exhibit autocatalytic decomposition. Inhibitor depletion can be a serious problem with certain vinyl monomers, such as styrene and acrylic acid, that can initiate polymerization at ambient temperatures and then selfheat into runaways. Isothermal DSC tests can be used to determine a time to runaway that is related to the inhibitor concentration. 

As discussed above, the degree of inhibition is indicated by the ratio of k3/k and defines an inhibitor constant (Kj) [Eq. (3.19)], whose value reports the dissociation of the enzyme-inhibitor complex (El) [Eq. (3.20)]. Deriving the equation for competitive inhibition under steady-state conditions leads to Eq. (3.21). Reciprocal plots of 1/v versus 1/5 (Lineweaver-Burk plots) as a function of various inhibitor concentrations readily reveal competitive inhibition and define their characteristic properties (Fig. 3.5). Notice that Vmax does not change. Irrespective of how much competitive inhibitor is present, its effect can be overcome by adding a sufficient amount of substrate, i.e., substrate can be added until Vmax is reached. Also notice that K i does change with inhibitor concentration therefore the Km that is measured in the presence of inhibitor is an apparent Km- The true KM can only be obtained in the absence of inhibitor. 

In vivo the corresponding parameter to a K is A iiv, a parameter that is determined directly from in vivo experiments. Theoretically, K and K should be equal, but for the reasons outlined above they may not be. K is a direct measure of the molecular interaction of the drug with the enzyme. A iiv on the other hand is a measure of the actual in vivo effectiveness of the inhibitor. That is /(" iv, unlike Kj, automatically incorporates into its value the effects of factors such as differences in active site inhibitor concentration,... 

Starting materials (specification, nature, properties), eg. Impurities with catalytic effect Concentration increases/ decreases Residues (heels) from previous use Lowering of activator/ inhibitor concentration (e.g. due to storage beyond expiration) ... 

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