Carbohydrate complexes stability constants

Where / is the RTP intensity for a particular concentration of carbohydrate /o is the initial intensity without carbohydrate while /nm is the limiting intensity K is the stability constant of the receptor with guest [C] is the concentration of carbohydrate. The stability constants of BrQBA-carbohydrate complex were obtained as 2.6x103 mol/L for fructose, 1.8xl03 mol/L for galactose, 1.6xl03 mol/L for glucose and 1.3x 103 mol/L for mannose, respectively. 

Discussion of the effect of ligand structure on protein-carbohydrate affinity requires an evaluation of complex stability constants. A munber of biophysical techniques are appropriate for the study of protein-carbohydrate interaction many of the more enlightening strategies are the topics of separate chapters elsewhere in this volume. We describe below three techniques used extensively in glycobiology— inhibition of hemagglutination, enzyme-linked lectin assay (ELLA), and isothermal titration microcalorimetry—and we consider the types of information provided by each technique in order to facilitate appropriate interpretation of the data. 

Stability Constants of Some Carbohydrate And Related Complexes by Potentiometric Titration... 

If it is true that the structural form of D-glucose which reacts with boric acid is the a-D-pyranose form, then that form probably exists in a boat or twist conformation in the complex. This implies that the study of the stability constants of sugar borate ester might give information about the ability of various carbohydrates to form such boat or twist conformations (10, 21). 

The measure of the strength of complex-formation between a cation (X" ") and a carbohydrate (Carb) is the stability (or formation) constant, defined as K = [Carb X ]/[Carb][X ]. The determination of the stability constants of cation-sugar complexes has not been wholly satisfactory. The constants being comparatively small, their accurate determination is difficult. The... 

Comparison of the complex-formation constants for bofli 1 1 (57 and 58) and 1 2 (such as 59) species ° with those obtained for the respective copper(II) complexes with parent amino acids revealed that the fructosyl moiety provides for an additional chelate effect in D-fructose-a-amino acids and as a consequence, a significant increase in the complex stability. In the absence of an anchoring chelating group, such as a-carboxylate, the D-finctosamine structure is not a good copper(II) chelator, and Cu(n) expectably does not form stable complexes with the carbohydrate in A -d-Iructose-L-lysine peptides. Although it would be expected that iron(III) complexes with D-finctose-amino acids in aqueous solutions, no related thermodynamic equilibrium studies have been done so far for this important redox-active metal. 

Reports of the kinetics of ceric oxidation of a variety of different alcohols have been made. The substrate molecules include mono-, di- and trihydroxyalkanes, cyclo-alkanols (cychc alkane alcohols) and phenols (table 3). Hydroxyacids have also been investigated and will be discussed in the section on carboxylic acids. Ceric oxidation of carbohydrates is discussed along with aldehydes and ketones. In those studies with excess substrate, the dominant products (where discussed) are the corresponding aldehydes and ketones. The most remarkable aspect of these investigations is that the resolved values for the stability constants of many of the precursor complexes exceed those observed in analogous Ce(lV)-carboxylic acid oxidations. 

Enzymic activities of crude soil suspensions have been demonstrated to follow Michaelis-Menten kinetics. Calculated Km values have varied for different soils and for active fractions of soil extracts. The extent to which kinetic constants of soil enzymes are influenced by the state in which the enzymes occur in soils, is unknown. For some activities, two Km values have been distinguished for the one crude soil extract. Fractionation has revealed that enzymes may exist in tightly- and loosely- bound complexes with soil coloured humic compounds. Enzymes freed of coloured materials may nevertheless still be bound in complexes by their association with carbohydrates. These may not only influence enzyme kinetic properties but evidence suggests that they may also confer some degree of stability on the enzymes in soil. Whereas early speculation on the mechanism(s) by which enzymes are protected in soil tended, in the case of abiontic enzymes, to focus on the role of clay or humic colloids, fractionation studies have drawn attention to the potentially important role of soil carbohydrates. The manner in which carbohydrates are bonded to the enzymes in soil has not as yet been established and may be a fruitful line of enquiry. 

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