Complexes dissociation constant

Fraction of easily accessible cavities Fluorescence intensity in the presence of analyte Initial fluorescence intensity in the analyte absence Current of anodic peak in LSV or CV Retention factor Acid dissociation constant Complex dissociation constant... 

The radioimmunoassay (RIA) for the determination of insulin developed by Yalow and Berson (1959) combined for the first time the high sensitivity of a ra-dioactively labeled compound with the high specificity of an immunological reaction by the formation of a thermodynamically stable antigen-antibody complex (dissociation constants are typically 10 9 -10 12 M). In this way it was possible to detect quantitatively substances in the attomolar range even in the presence... 

Most, if not all, contemporary applications of immunochemical techniques are based on the reaction of antibodies with the antigen used to induce their production, to yield a very stable complex. If both antigen and antibody are present in solution, a precipitate forms as long as the antibody is in molar excess. This is known as a precipitin reaction and may be quantitated as shown in Figure 8-15. For this example a highly purified preparation of avidin was injected into a rabbit which then produced avidin-specific antibodies. Since biotin forms a very stable complex (dissociation constant with avidin, complexation of... 

Data obtained under these conditions can be fitted using a least-squares procedure based upon the exact solution to the differential equations describing this mechanism [37, 44]. This yields values for the complex dissociation constant Ky, and the limiting first-order rate constant (a minimum value for the second-order rate constant for complex formation can also be obtained from this analysis). Note that AId refers to the interaction between reduced P and oxidized P, a situation that is observable only by kinetic methodology. 

Competitive inhibitors are so named because they compete for the active site with the native substrate, meaning that only enzyme-inhibitor or enzyme-substrate complex formation is possible (Fig. 7-3a). In this case, the inhibition constant, or enzyme-inhibitor complex dissociation constant, can be defined ... 

Many foodstuffs contain a metabolic intermediate of biotin, biocytin s-N-biotinyUysine), which is cleaved in the intestinal tract by the enzyme biotinidase. Only free biotin can be resorbed in the proximal small intestine, a process, which can be blocked by avidin, a glycoprotein with a molar mass of ca. 70,000. Avidin occurs in greater amounts in egg-white, and forms with biotin an extraordinarily stable molecular complex (dissociation constant at 25 °C K = 10 M), which can be cleaved neither by acids nor by peptidases. Only irradiation or longer exposure to heat leads to denaturation of avidin and thereby the release of biotin. This is another reason why a breakfast egg ought to be cooked for at least AVi minutes. In this way avidin is denatured and loses its harmful effect. Similarly stable complexes are formed by biotin with neutravidin (de-glycosyl-ated avidin), streptavidin and stravidin from certain Streptomyces and Saccharo-myces species respectively. 

An alternative approach is to consider the organic phase as ideal and adopt the deviations from ideality, introducing a more complex chemistry. Wenzel and Maurer [26] assumed the organic phase to be ideal and that there exist a Zn-(DEHP)2 and a Zn-(DEHP)4 complex simultaneously in the organic phase. The complex dissociation constants are estimated according to the following equations ... 

Fig 6 Correlation between complex dissociation constant, (lOO-lOOOO) dissolution volume (10-1000 ml), and dissolved drug in % (Free + complexed). Hypothetic solubility of the complex 10" mol/l. Black area free dissolved drug, vertically hatched area dissolved complexed drug. 

Determination of equilibrium constants, including. solubility and complex dissociation constants, phase distribution ill solvent extraction, adsorption, ion exchange, coprecipitation and kinetic data, such as rate constants... 

Calcium complex dissociation constants were calculated following a modification of a previously described method." The dissociation constant P of the calcium complex as defined by equation (1) may be calculated using equation (2). Equation (2) was derived assuming the concentration of free calcium ions is negligible at the turbidimetric end point. 

Michaelis constant An experimentally determined parameter inversely indicative of the affinity of an enzyme for its substrate. For a constant enzyme concentration, the Michaelis constant is that substrate concentration at which the rate of reaction is half its maximum rate. In general, the Michaelis constant is equivalent to the dissociation constant of the enzyme-substrate complex. 

Indicator Chemical name Dissociation constants and colors of free indicator species Colors of metal-indicator complexes Applications... 

The equilibrium constant for a reaction in which a metal—ligand complex dissociates to form uncomplexed metal ion and ligand (Kd). 

Combinatorial Hbraries are limited by the number of sequences that can be synthesized. For example, a Hbrary consisting of one molecule each of a 60-nucleotide sequence randomized at each position, would have a mass of >10 g, weU beyond the capacity for synthesis and manipulation. Thus, even if nucleotide addition is random at all the steps during synthesis of the oligonucleotide only a minority of the sequences can be present in the output from a laboratory-scale chemical DNA synthesis reaction. In analyzing these random but incomplete Hbraries, the protocol is efficient enough to allow selection of aptamers of lowest dissociation constants (K ) from the mixture after a small number of repetitive selection and amplification cycles. Once a smaller population of oligonucleotides is amplified, the aptamer sequences can be used as the basis for constmcting a less complex Hbrary for further selection. 

Table 3. Equilibrium Dissociation Constants for Drug—Receptor Complexes In Vitro...

Cyanide Complexes. Insoluble silver cyanide, AgCN, is readily dissolved in an excess of alkah cyanide. The predominant silver species present in such solutions is Ag(CN) 2) with some Ag(CN) 3 and Ag(CN) 4. Virtually all silver salts, including the insoluble silver sulfide, dissolve in the presence of excess cyanide because the dissociation constant for the Ag(CN) 2 complex is only 4 x 10 (see Cyanides). 

Himdin [8001-27-2] is a polypeptide of 66 amino acids found ia the saUvary gland secretions of the leech Himdo medicinalis (45). It is a potent inhibitor of thrombin and biads to y-thrombia with a dissociation constant of 0.8 x 10 ° M to 2.0 x lO " M. Himdin forms a stable noncovalent complex with free and bound thrombin completely iadependent of AT-III. This material has now been cloned and expressed ia yeast cells (46,47). Its antigenic poteatial ia humans remains to be estabUshed. 

The substrate concentration when the half maximal rate, (Vmax/2), is achieved is called the Km. For many simple reactions it can easily be shown that the Km is equal to the dissociation constant, Kd, of the ES complex. The Km, therefore, describes the affinity of the enzyme for the substrate. For more complex reactions, Km may be regarded as the overall dissociation constant of all enzyme-bound species. 

The Michaelis constant has the units of a dissociation constant however, the dissociation constant of the enzyme—substrate complex is k dk, which is not equal to Km unless k 2-... 

There are important consequences for this statement. The enzyme must stabilize the transition-state complex, EX, more than it stabilizes the substrate complex, ES. Put another way, enzymes are designed by nature to bind the transition-state structure more tightly than the substrate (or the product). The dissociation constant for the enzyme-substrate complex is... 

Thus, the enzymatic rate acceleration is approximately equal to the ratio of the dissociation constants of the enzyme-substrate and enzyme-transition-state complexes, at least when E is saturated with S. 

---