Specific Binding of 8-Anilinonaphthalene Sulfonate to Diphosphopyridine Nucleotide-linked Isocitrate Dehydrogenase from Bovine Heart

Binding of 1-anilinonaphthalene-8-sulfonic acid to alpha-crystallin

alpha-Crystallin was found to exhibit a time-dependent uptake of the hydrophobic probe, 1-anilinonaphthalene-8-sulfonic acid (ANS), similar to that typically observed with lipid membranes. Analysis of the interaction of ANS with alpha-crystallin revealed two types of interactive processes, partitioning and binding. The predominant process involved partitioning, with a coefficient of 300 M-1. The binding component had the following characteristics: 1 binding site/24 subunits and a Kd of about 9 microM. The binding was unaffected by the number of subunits used in the assembly of the alpha-aggregate, since both the alpha m- and alpha c-forms had similar binding characteristics. No discernible differences were observed in the binding of ANS to homopolymers of alpha A and alpha B subunits, suggesting that the hydrophobic sites to which ANS bound were similar in both the A and B subunits. The majority of the fluorescence was lost when the protein was incubated in 3 M urea, a concentration of denaturant where the protein is still intact, suggesting that the ANS binding sites are located near the surface of the protein. The decrease was attributed to a decrease in the quantum yield of the bound dye.

Adenine nucleotides affect the binding of 3-phosphoglycerate to pig muscle 3-phosphoglycerate kinase

Pig muscle 3-phosphoglycerate kinase was complexed with 1-anilino-8-naphthalenesulfonate (ANS) in order to monitor the binding of substrates to the enzyme. The enzyme-dye interaction did not influence the enzymic activity under the experimental conditions used. By measuring the substrate-dependent change in the fluorescence emission of ANS molecules tightly bound to the enzyme (Kd less than or equal to 0.05 mM), fluorimetric titrations were carried out in 0.1 M Tris/HCl buffer pH 7.5, containing 5 mM mercaptoethanol, at 20 degrees C. The dissociation constants obtained for the separate bindings of 3-phosphoglycerate, MgATP, 1,3-bisphosphoglycerate and MgADP were 0.03 +/- 0.01 mM, 0.15 +/- 0.10 mM, 0.00005 +/- 0.00001 mM and 0.15 +/- 0.10 mM respectively. binding of 3-phosphoglycerate is weakened when MgATP is also bound to the enzyme: the dissociation constant of 3-phosphoglycerate in this ternary complex (0.25 +/- 0.08 mM) is comparable to its Km value (0.38 +/- 0.10 mM). The same weakening can be observed in the non-productive ternary complexes where MgATP is replaced by MgADP (Kd = 0.20 +/- 0.10 mM) or AMP (Kd = 0.12 +/- 0.05 mM), whereas adenosine has no such effect. This indicates the importance of the negatively charged phosphate(s) of nucleotides in influencing the binding of 3-phosphoglycerate. In contrast to 3-phosphoglycerate, the binding of the substrate analogue, glycerol 3-phosphate is practically not affected by the presence of MgATP: the dissociation constant to the free enzyme (0.40 +/- 0.10 mM) is comparable to its inhibitory constant (0.70 +/- 0.20 mM). This finding and the similarity of the dissociation constant of glycerol 3-phosphate binding (0.40 +/- 0.10 mM) and the Km value of 3-phosphoglycerate (0.38 +/- 0.10 mM) suggest that, during the enzymic reaction, binding of 3-phosphoglycerate occurs probably without involvement of the carboxyl group.

Fluorescent probe study with 1-anilino-8-naphthalene sulfonate on acetylglutamate activation, ATP binding and conformational changes of the rat liver carbamoyl-phosphate synthetase

The activity and stability of carbamoyl-phosphate synthetase (EC 6.3.4.16) may involve hydrophobic and ionic bonds within the enzyme. The 1-anilino-8-naphthalene sulfonate (ANS) equilibrium binding method with hydrophobic and ionic sites in enzymes, therefore, seemed suitable for the study of the acetylglutamate activation and ATP binding of the enzyme. The enzyme had a high affinity for the dye but low fluorescent yields. The enzyme had 32-88 ANS binding sites, depending on combination with ATP and acetylglutamate, and individual affinity constants for each combination. Despite the large number of binding sites, the acetylglutamate and ATP concentrations for half-maximal fluorescent change (10-40 microM) corresponded to the high-affinity bound ATP (ATPB) and acetylglutamate Kd values. In kinetic studies, ANS competed with ATP or acetylglutamate. The extrapolated ANS Ki values for ATP or acetylglutamate were both 35 microM. This value agreed with the ANS Kd value of the enzyme X ATP conformation, indicating that this was the conformation competed for by ANS. Since ANS did not influence the HCO3-dependent ATPase, ANS was concluded to compete with the ATPB binding conformation and transitional changes. This study suggests that part of the activator role of acetylglutamate may be to change the tertiary structure of the enzyme to induce hydrophobic sites which are accessible to ANS and possibly at the ATPB site.

Conformational changes associated with the reversible cold inactivation of ribulose-1,5-bisphosphate carboxylase-oxygenase

Crystalline ribulose-1,5-bisphosphate carboxylase-oxygenase (3-phospho-D-glycerate carboxy-lyase (dimerising), EC 4.1.1.39) isolated from tobacco (Nicotiana tabacum L.) leaf homogenates is partially inactivated by cold treatment and fully reactivated by simple heating in the absence of sulfhydryl reagents and effectors. Since the reversible cold inactivation of this bifunctional enzyme does not involve a gross change in the association state of subunits, a subtle conformational change induced by low temperatures was implicated (Chollet, R. and Anderson, L.L. (1976) Arch. Biochem. Biophys. 176, 344-351). Chemical modification of the cold-inactivated and heat-reactivated enzymes by 5,5'-dithiobis-(2-nitrobenzoate) and p-mercuribenzoate at 25 degrees C revealed no difference in the number of free -SH groups per mol protein. However, the reactivity of the sulfhydryl residues on the inactivated protein was considerably greater than that of the reactivated enzyme. Pretreatment of the two proteins with sodium dodecyl sulfate completely abolished the difference in -SH reactivity, indicating its dependence on protein conformation. Both the cold-inactivated and heat-reactivated enzymes enhanced the fluorescence intensity of 8-anilino-1-naphthalenesulfonate (ANS) and caused a blue shift of the emission maximum from 510 to 472 nm. When the inactivated enzyme was reactivated by heating, the increase in catalytic activity was closely paralleled by a concomitant decrease in the fluorescence intensity of the ANS - protein complex at 25 degrees C. Fluorescence titration experiments revealed that the decrease in fluorescence intensity accompanying heat reactivation of the inactivated enzyme was due to a reduction in the number of hydrophobic sites available for ANS binding rather than to a change in the dissociation constant of the ANS - protein complex. These results indicate that the reversible cold inactivation of ribulose-1,5-bisphosphate carboxylase-oxygenase is associated with a reversible change in the conformation of the protein. This cold-induced conformational change resluts in a greater exposure of sulfhydryl groups and hydrophobic regions to the external environment and is closely paralleled by changes in the catalytic activity of the protein. By analogy to other oligomeric enzymes also subject to reversible cold inactivation, perhaps low temperatures induce a partial dissociation of the octameric structure of the hydrophobic catalytic subunits, but complete dissociation is arrested in some unknown manner by the small hydrophilic subunits.

Stopped-flow studies of changes in fluorescence of 8-anilino-1-naphthalene sulfonic acid caused by magnesium and salt binding to yeast enolase

Stopped-flow studies of magnesium and salt (potassium chloride and acetate) effects on yeast enolase were carried out by following 8-anilino-1-naphthalenesulfonic acid fluorescence changes. The fluorescence changes appear to be largely caused by subunit association and dissociation, though there is evidence in some reactions for large changes in fluorescence occurring within the dead time of the stopped-flow measurements. These data are combined with measurements of initial enzyme activity after incubation in various solvents with or without magnesium to obtain subunit association and dissociation rates. From these, it is concluded that magnesium and the salts act by directly changing the affinities of the subunits for each other, apparently by producing a rapid change in protein conformation.