Dynamics of heme complexed with human serum albumin: a theoretical approach.

Human serum albumin (HSA) is the most abundant protein in the blood serum. It binds several ligands and has an especially strong affinity for heme, hence becoming a natural candidate for oxygen transport. In order to analyze the interaction of HSA-heme, molecular dynamics simulations of HSA with bound heme were performed. Based on the results of X-ray diffraction, the binding site of the heme, localized in subdomain IB, was considered. We analyzed the fluctuations and their correlations along trajectories to detect collective motions. The role of H bonds and salt bridges in the stabilization of heme in its pocket was also investigated. Complementarily, the localization of water molecules in the hydrophobic pocket and the interaction with heme were discussed.

Hydration of hydrophobic biological porphyrins.

Explicit solvent, single solute molecular dynamics simulations of protoporphyrin IX and its Fe(2+) complex (heme) in water were performed. The relation of solute-solvent was examined through the spatial distribution functions of water molecules around the centroid of the porphyrin ring. A detailed description of the time-averaged structure of water surrounding the solutes as well as of its fluctuations is presented.

Versatile magnetometer assembly for characterizing magnetic properties of nanoparticles.

We constructed a versatile magnetometer assembly for characterizing iron oxide nanoparticles. The magnetometer can be operated at room temperature or inside a cryocooler at temperatures as low as 6 K. The magnetometer's sensor can be easily exchanged and different detection electronics can be used. We tested the assembly with a non-cryogenic commercial Hall sensor and a benchtop multimeter in a four-wire resistance measurement scheme. A magnetic moment sensitivity of 8.5 × 10(-8) Am(2) was obtained with this configuration. To illustrate the capability of the assembly, we synthesized iron oxide nanoparticles coated with different amounts of a triblock copolymer, Pluronic F-127, and characterized their magnetic properties. We determined that the polymer coating does not affect the magnetization of the particles at room temperature and demonstrates that it is possible to estimate the average size of coating layers from measurements of the magnetic field of the sample.

Inhibition of acetylcholinesterase from Electrophorus electricus (L.) by tricyclic antidepressants.

The effects of tricyclic antidepressants drugs (TCA) amitriptyline, imipramine and nortriptyline, on purified Electrophorus electricus (L.) acetylcholinesterase (AChE; acetylcholine hydrolase, EC 3.1.1.7) were studied using kinetic methods and specific fluorescent probe propidium. The antidepressants inhibited AChE activity by a non-competitive mechanism. Inhibition constants range from 200 to 400 microM. Dimethylated amitriptyline and imipramine were more potent inhibitors than the monomethylated nortriptyline. Fluorescence measurements using bis-quaternary ligand propidium were used to monitor ligand-binding properties of these cationic antidepressants to the AChE peripheral anionic site (PAS). This ligand exhibited an eight-fold fluorescence enhancement upon binding to the peripheral anionic site of AChE from E. electricus (L.) with K(D)=7 x 10(-7)M. It was observed that TCA drugs displaced propidium from the enzyme. On the basis of the displacement experiments antidepressant dissociation constants were determined. Similar values for the inhibition constants suggest that these drugs have similar affinity to the peripheral anionic site. The results also indicate that the catalytic active center of AChE does not participate in the interaction of enzyme with tricyclic antidepressants. These studies suggest that the binding site for tricyclic antidepressants is located at the peripheral anionic site of E. electricus (L.) acetylcholinesterase.

Quenching of the intrinsic fluorescence of bovine serum albumin by chlorpromazine and hemin.

The binding of chlorpromazine (CPZ) and hemin to bovine serum albumin was studied by the fluorescence quenching technique. CPZ is a widely used anti-psychotic drug that interacts with blood components, influences bioavailability, and affects function of several biomolecules. Hemin is an important ferric residue of hemoglobin that binds within the hydrophobic region of albumin with high specificity. Quenching of the intrinsic fluorescence of bovine serum albumin (BSA) was observed by selectively exciting tryptophan residues at 290 nm. Emission spectra were recorded in the range from 300 to 450 nm for each quencher addition. Stern-Volmer graphs were plotted, and the quenching constant estimated for BSA solution titrated with hemin at 25 masculine C was 1.44 (+/- 0.05) x 10(5) M(-1). Results showed that bovine albumin tryptophans are not equally accessible to CPZ, in agreement with the idea that polar or charged quenchers have more affinity for amino acid residues on the outer wall of the protein. Hemin added to albumin solution at a molar ratio of 1:1 quenched about 25% of their fluorescence. The quenching effect of CPZ on albumin-hemin solution was stronger than on pure BSA. This increase can be the result of combined conformational changes in the structure of albumin caused firstly by hemin and then by CPZ. Our results suggest that the primary binding site for hemin on bovine albumin may be located asymmetrically between the two tryptophans along the sequence formed by subdomains IB and IIA, closer to tryptophan residue 212.

Quenching of the intrinsic fluorescence of bovine serum albumin by chlorpromazine and hemin

The binding of chlorpromazine (CPZ) and hemin to bovine serum albumin was studied by the fluorescence quenching technique. CPZ is a widely used anti-psychotic drug that interacts with blood components, influences bioavailability, and affects function of several biomolecules. Hemin is an important ferric residue of hemoglobin that binds within the hydrophobic region of albumin with high specificity. Quenching of the intrinsic fluorescence of bovine serum albumin (BSA) was observed by selectively exciting tryptophan residues at 290 nm. Emission spectra were recorded in the range from 300 to 450 nm for each quencher addition. Stern-Volmer graphs were plotted, and the quenching constant estimated for BSA solution titrated with hemin at 25ºC was 1.44 (± 0.05) x 10(5) M-1. Results showed that bovine albumin tryptophans are not equally accessible to CPZ, in agreement with the idea that polar or charged quenchers have more affinity for amino acid residues on the outer wall of the protein. Hemin added to albumin solution at a molar ratio of 1:1 quenched about 25 percent of their fluorescence. The quenching effect of CPZ on albumin-hemin solution was stronger than on pure BSA. This increase can be the result of combined conformational changes in the structure of albumin caused firstly by hemin and then by CPZ. Our results suggest that the primary binding site for hemin on bovine albumin may be located asymmetrically between the two tryptophans along the sequence formed by subdomains IB and IIA, closer to tryptophan residue 212.