The Binding of Organic Ions by Proteins. Effect of Temperature

A spectrofluorometric investigation, using 1-anilino-naphthalene-8-sulphonate, of the interaction between washed bovine spermatozoa and seminal plasma or egg-yolk lipoprotein

“…KD was determined as the negative of the value calculated for the gradient and as the ordinate intercept (Table 1). Alternatively, the reciprocal of the concentration of ANS bound was plotted against the reciprocal of the concentration of unbound dye (Klotz, Walker & Pivan, 1946;Laurence, 1952;Weber & Young, 1964a, b;Mercado & Rosado, 1973 (Text-fig. 7).…”

A time-dependent, two-step binding mode of the nitro dye flavianic acid to trypsin in acid media

“…In this way, anions of the size of flavianate, methyl orange, Biebrich scarlet and Congo red should have aromatic surface areas directly related to their values of free binding energy ( Table 2). The entropy-driven character of flavianate binding to trypsin was not tested at different temperatures since a negligible or neutral thermal effect was found in the past on isotherms of organic dyes with proteins (39). Meanwhile, preliminary calorimetric assays performed by us showed a positive enthalpy value of the same order of magnitude as the free energy of binding, with an entropy change DS of +26.3 entropy units.…”

“…This is within the -1.7 kJ/mol range suggested by Rosemberg (17) as typical entropy-driven force of weak interactions due to water displacement from the hydration shell of the protein surface. At the molecular level, a higher affinity for some larger anions may be pL -log (a/ [1 -a] due to a greater degree of dehydration of the complex rather than to increased van der Walls interactions (39). In this way, anions of the size of flavianate, methyl orange, Biebrich scarlet and Congo red should have aromatic surface areas directly related to their values of free binding energy ( Table 2).…”

“…A few years later, Chapman et al (2) observed the correspondence between the amount of dye bound and the number of proton-binding groups in the protein. With the application of the mass action law to multiple equilibria, a theoretical basis became available for the thermodynamic treatment of dye-protein complexes (3). The ability of ionic dyes to precipitate proteins has long since been used in studying protein behavior upon unfolding, protection against denaturants, preservation of macromolecule conformation during stress, and bioseparation (4).…”

Protein binding of chloroquine in the presence of aspirin.

“…To determine the effect of aspirin on the degree of binding of chloroquine, acetylsalicylic acid and chloroquine were added to the buffer solution in the Quickfit tube in the ratio of 1:1 by weight. Chloroquine was estimated by a modification (Adelusi & Salako, 1980) of the fluorimetric method of Rubin et al (1965) and correction was made for adsorption to the sack in calculating the percentage of protein-bound drug (Klotz et al, 1946).…”