PubMed Health⌕ Search

Biomedical subjects

Jaroslava Miksovská

Publications and source records attributed to Jaroslava Miksovská.

9 recordsLinked to original sources
PubMed2006

Characterization of carbon monoxide photodissociation from Fe(II)LPO with photoacoustic calorimetry.

Lactoperoxidase belongs to a family of mammalian peroxidases that catalyze the oxidation of halides and small organic molecules in the presence of H2O2. We have used photoacoustic calorimetry to characterize thermodynamic parameters associated with ligand dissociation from bovine milk lactoperoxidase. Upon CO photorelease, a prompt (tau < 50 ns) exothermic volume contraction (DeltaH = -20 +/- 7 kcal mol-1 and DeltaH = -2 +/- 1 mL mol-1) was measured at pH 7.0 and 4.0, whereas an endothermic expansion (DeltaH = 30 +/- 13 kcal mol-1 and DeltaV = 9 +/- 2 mL mol(-1)) was observed at pH 10.0 and 7.0 in the presence of 500 mM NaCl. We attribute the observed volume and enthalpy changes to electrostriction arising from changes in the charge distribution associated with a reorganization of the heme binding pocket upon ligand dissociation. It is likely that cleavage of the Fe-CO bond is accompanied by distortion of a salt bridge between Arg557 and the heme propionate group, resulting in the observed electrostriction due to changes in charge distribution.

Animals↗
PubMed2006

Spectroscopic and photothermal study of myoglobin conformational changes in the presence of sodium dodecyl sulfate.

Interactions between sodium dodecyl sulfate (SDS) and horse heart myoglobin (Mb) at surfactant concentrations below the critical micelle concentration have been studied using steady-state and transient absorption spectroscopies and photoacoustic calorimetry. SDS binding to Mb induces a heme transition from high-spin five-coordinate to low-spin six-coordinate in met- and deoxyMb, with the distal His residue likely to be the sixth ligand. The transition is complete at an SDS concentration of approximately 350 microM and approximately 700 microM for met- and deoxyMb, respectively. DeltaG(H(2)O) and m values determined from equilibrium SDS-induced unfolding curves indicate similar stability of met- and deoxyMb toward unfolding; however, the larger m value for the deoxyMb equilibrium intermediate indicates that its structure differs from that of metMb. Results from transient absorption spectroscopy show that CO rebinding to Fe(2+)-Mb in the presence of SDS is a biphasic process with the rate constant of the first process approximately 5.5 x 10(3) s(-1), whereas the second process displays a rate similar to that for CO rebinding to native Mb (k(obs) = 7.14 x 10(2) s(-1)) at 1 mM CO. Results of photoacoustic calorimetry show that CO dissociation from deoxyMb occurs more than 10 times faster in the presence of SDS than in native Mb. These data suggest that the heme binding pocket is more solvent-exposed in the SDS-induced equilibrium intermediate relative to native Mb, which is likely due to the electrostatic and hydrophobic interactions between surfactant molecules and the protein matrix.

Animals↗
PubMed2005

Characterization of conformational changes coupled to ligand photodissociation from the heme binding domain of FixL.

Using transient absorption spectroscopy and photoacoustic calorimetry (PAC), we have characterized carbon monoxide photodissociation and rebinding to two forms of the heme domain of Bradyrhizobium japonicum FixL. Transient absorption results for the complete heme domain (FixL residues 140-270) and a truncated heme domain (missing 11 residues on the N-teminal end and 14 amino acid residues on the C-terminal end of the full length heme domain) show similar rates for ligand rebinding to the five-coordinate heme domain and the absence of any transient intermediate on a microsecond time scale. Results from PAC studies show that both the truncated and complete heme domains undergo a contraction upon ligand photolysis. In addition, CO photolysis from the complete heme domain gives rise to an intermediate with a lifetime of approximately 150 ns which is absent in the truncated heme domain. We attribute the 150 ns phase to ligand release to the solvent which may be accelerated in the case of the truncated domain. The initial contraction is attributed to changes in the charge distribution due to reorganization of the surface salt bridge formed between Glu182 and Arg227 or possibly to reorientation of Arg206. Changes in the charge distribution may play an important role in communication between the sensor domain and the regulatory domain and thus may be part of the signal transduction pathway.

Bacterial Proteins↗
PubMed2005

Photothermal studies of CO photodissociation from mixed valence Escherichia coli cytochrome bo3.

Here, we report the volume and enthalpy changes accompanying CO photodissociation from the mixed valence form of cytochrome bo3 oxidase from Escherichia coli. The results of photoacoustic calorimetry indicate two kinetic phases with distinct volume and enthalpy changes accompanying CO photodissociation from heme o3 and its transfer to CuB. The first phase occurring on a timescale of <50 ns is characterized by a volume decrease of -1.3+/-0.3 mL mol-1 and enthalpy change of 32+/-1.6 kcal mol-1. Subsequently, a volume increase of 2.9 mL mol-1 with an enthalpy change of -5.3+/-2.5 kcal mol-1 is observed with the lifetime of approximately 250 ns (this phase has not been detected in previous optical studies). These volume and enthalpy changes differ from the volume and enthalpy changes observed for CO dissociation from fully reduced cytochrome bo3 oxidase indicating that the heme o3/CuB active site dynamics are affected by the redox state of heme b.

Carbon Monoxide↗
PubMed2005

Thermodynamic profiles for CO photodissociation from heme model compounds: effect of proximal ligands.

Here we present a comprehensive study of the thermodynamic parameters (enthalpy, entropy, and volume changes) associated with carbon monoxide photodissociation and rebinding to Fe(II) microperoxidase-11 (Fe(II)MP11) and Fe(ll) tetrakis(4-sulfonatophenyl)porphine complex (FeII4SP) with water and 2-methylimidazole as proximal ligands. CO photodissociation from FeII4SP complexes is accompanied by a positive volume change of approximately 17 mL mol(-1). A smaller volume change of approximately 12 mL mol(-1) was observed for CO dissociation from Fe(II)MP-11. We attribute the positive volume change to cleavage of the Fe-CO covalent bond and to solvent reorganization due to the low-spin to high-spin transition. CO binding is an exothermic reaction with an enthalpy change of -17 kcal mol(-1) for the CO-FeII4SP complexes and -13 kcal mol(-1) for the CO-Fe(II)MP11 complex. In all cases, the ligand recombination occurs as a single-exponential process indicating that CO dissociation is followed by direct CO rebinding to a high-spin five-coordinate complex without concomitant dissociation of the proximal base. In addition, observed negative activation entropies and volumes for ligand binding to (2-Melm)FeII4SP and MP-11, respectively, suggest that CO rebinding can be described by an associative mechanism with bond formation being the rate-limiting step.

Journal Article↗
PubMed2004

Time-resolved photoacoustics study of the ruthenium(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-2,2'-bipyridine) complex.

The formation and the decay of the triplet metal to ligand charge transfer state ((3)MLCT) of ruthenium(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-2,2'-bipyridine) (Ru(bpy)(2)(dcbpy)) were characterized using photoacoustic calorimetry. At pH 6 and 2, the (3)MLCT state formation leads to a volume change of -8 mL mol(-1) and enthalpy changes of 17 kcal mol(-1) and 13 kcal mol(-1), respectively. We attribute the volume contraction to structural changes and to solvent electrostriction. At pH 4, the photoexcitation of the complex leads to an expansion of 14 mL mol(-1) and an enthalpy change of approximately 119 kcal mol(-1) due to protonation of the carboxyl group in the excited state.

Journal Article↗
PubMed2003

Volume and enthalpy profiles of CO rebinding to horse heart myoglobin.

Carbon monoxide binding to myoglobin was characterized using the photothermal beam deflection method. The volume and enthalpy changes coupled to CO dissociation were found to be 9.3+/-0.8 mL x mol(-1) and 7.4+/-2.8 kcal x mol(-1), respectively. The corresponding values observed for CO rebinding have the same magnitude but opposite sign: Delta V=-8.6+/-0.9 mL x mol(-1) and Delta H=-5.8+/-2.9 kcal x mol(-1). Ligand rebinding occurs as a single conformational step with a rate constant of 5 x 10(5) M(-1) s(-1) and with activation enthalpy of 7.1+/-0.8 kcal x mol(-1) and activation entropy of -22.4+/-2.8 cal x mol(-1) K(-1). Activation parameters for the ligand binding correspond to the activation parameters previously obtained using the transient absorption methods. Hence, at room temperature the CO binding to Mb can be described as a two-state model and the observed volume contraction occurs during CO-Fe bond formation. Comparing these results with CO dissociation reactions, for which two discrete intermediates were characterized, indicates differences in mechanism by which the protein modulates ligand association and dissociation.

Animals↗
PubMed2003

Photothermal studies of pH induced unfolding of apomyoglobin.

Conformational dynamic and enthalpy changes associated with pH induced unfolding of apomyoglobin were studied using photoacoustic calorimetry and photothermal beam deflection methods. The transition between the native state and the I intermediate was induced by a nanosecond pH jump from o-nitrobenzaldehyde photolysis. Deconvolution of photoacoustic waves indicates two kinetic processes. The fast phase (T < 50 ns) is characterized by a volume expansion of 8.8 ml mol(-1). This process is followed by a volume contraction of about -22 ml mol(-1) (tau approximately 500 ns). Photothermal beam deflection measurements do not reveal any volume changes on the time scale between approximately 100 micros and 5 ms. We associate the volume contraction with structural changes occurring during the transition between the native state and the I intermediate. The lack of any processes on the ms time scale may indicate the absence of structural events involving larger conformational changes of apomyoglobin after the pH jump.

Acoustics↗