Inhibition curves

Antagonists can produce varying combinations of dextral displacement and depression of maxima of agonist dose-response curves. The concentration-related effect of an antagonist on the system response to a single concentration of agonist constitutes what will be referred to as an inhibition curve. One of the most straightforward examples... 

Under ideal conditions, inhibition curves should be obtained by blockade of an EC50 concentration of agonist. 

The inhibition curves are fit to an appropriate function to allow estimation of the half maximal value for blockade (IC50). For example, the data... 

It can be seen from this example that the inhibition curve shifts to the left with increasing concentration of agonist, indicating an allosteric mechanism whereby the modulator blocks receptor signaling but increases the affinity of the receptor for the agonist. 

Fig. 4 Plateaus in dose response inhibition curves are a phenotypic marker of resistance to maraviroc...

HIV phenotype A type of resistance testing for human immunodeficiency virus (HIV) in which a patient s blood sample is obtained, and the patient s HIV genes that encode for reverse transcriptase and protease are removed and placed in an HIV viral vector. This viral vector is replicated in a cell culture system with varying concentrations of antiretrovirals. A drug concentration-viral inhibition curve is developed and the concentration needed to inhibit 50% of the patient s virus is reported. This is used to predict resistance versus susceptibility. 

Vary Ks and K] to observe the changes in the inhibition curve by plotting versus S. Note especially the value of S at the maximum in /i. 

NMR screening methods can detect very weak binders, which shifts the measurable inhibition curve (Fig. 18.6) toward less complex molecules. So, it is theoretically more... 

Comparison of inhibition curves generated by four compounds following serial dilution in assay buffer containing 1% (v/v) DMSO (circles) and in neat DMSO (triangles) in a protein tyrosine kinase assay. 

In all cases, the percent of inhibition (/%) was determined by comparing the response given by a control solution to the sample solution. After that, an inhibition curve was fitted to... 

Competitive Inhibition in the Enzyme-Immunoassay with Purified Polyethers Including Ciguatoxin. Figure 2 represents an inhibition curve in the competitive test between a positive fish tissue and highly purified CTX (LD = 0.25 yg/kg mouse) in suspension. Approximately 0.002 ng of purified ciguatoxin gave 50% inhibition of the normal binding between sheep anti-CTX and the toxic fish tissue (Lutj anus sp.). 

The DDI conventional inhibition screen is moderate throughput and can range from a few compounds per week to a few hundred per week depending on the amount of inhibitor concentrations, inhibition curve replicates and analytical methods used. This screen typically uses 96- or 384-well formats. The reaction components (HLM, 100 mM potassium phosphate buffer, specific probe substrate, NCE, NADPH cofactor or NAD PH-regenerating system) are pre-warmed to 37 °C and are mixed together to initiate the reaction, then incubated at 37 °C for the appropriate length of... 

The enzyme has been partially purified (70-fold) from 38,000 X 9 supernatant fluid from sheep brain homogenates by Ipata (55-58). Thq enzyme (MW 140,000) is reported to be specific for 5 -AMP and 5 -IMP although the substrate specificity does not appear to have been examined closely. 2 - and 3 -AMP are not hydrolyzed (56). Unlike the enzyme from many sources the brain enzyme does not require divalent cations and indeed Co2+, which stimulates several other 5 -nucleotidases, was inhibitory at 5 mM. The enzyme is strongly inhibited by very low concentrations of ATP, UTP, and CTP (50% inhibition by 0.3 pM ATP) but not by GTP. 2 -AMP, 3 -AMP, and a variety of other nucleoside monophosphates, nucleosides, and sugar phosphates do not inhibit. A kinetic examination of ATP, UTP, and CTP inhibition (56-58) revealed that inhibition curves were sigmoidal, indicating cooperativity between inhibitor molecules and an allosteric type of interaction between inhibitor and protein. The metabolic significance of ATP inhibition is... 

A summary of the transition temperatures of RNase in the presence of a variety of electrolytes is given in Table XX 361, 362). The effects of the usual salts follow the Hofmeister series. The remarkable difference in denaturing power of the various guanidinium salts is quite general. The sulfate actually tends to stabilize slightly while the thiocyanate is a more powerful denaturant than the chloride. Irreversible denaturation is markedly inhibited by spermine 363). There is no clear correlation between stabilizing effects and the complex inhibition curves obtained by Wold (see Section VI,E,2). 

Figure 6.7 Ligand screening of a bacterial membrane protein. (A) The structure of Ubiquinone-5 used to asses the integrity of immobilized Dsbfi during the screen. (B) Ubiquinone-5 binding to immobilized DsbB during the screen. Binding is defined as in Rgure 6.5. (C) Tnzyme inhibition curve of a hit from the screen.

Figure 2 represented a log-probit plot of the observed inhibition of purified bovine erythrocyte acetylcholinesterase as a function of concentration for several of the transformation products of aminocarb. The observation that these inhibition curves are parallel suggests a similar mechanism of interaction for the various derivatives. The parameter I5f. (the concentration of inhibitor required to achieve 50% inhibition oi the enzyme activity) for each of the inhibitors were calculated and are recorded in Table 1. These values are reported relative to the parent compound aminocarb = 1. Also included in Table 1 are the relative toxicities of several of these products to house crickets (Acheta domesticus). It had been our intention to develop bioassay tests using the target insect itself, the eastern spruce budworm (Choristoneura fumiferana). However, spray tower results were quite variable and it was considered that genetic variability of the stock culture made the production of uniform test batches difficult to achieve. Using the house crickets, an LD q of 130-155 ppm for aminocarb standard was observed over the course of more than 25 bioassays. Also included in Table 1 are observations by Abdel-Wahab and Casida (19) using human plasma or house fly head cholinesterases. 

---