Biomedical subjects

Andrzej Sienkiewicz

Publications and source records attributed to Andrzej Sienkiewicz.

3 recordsLinked to original sources

PubMed2006

Multi-frequency high-field EPR study of iron centers in malarial pigments.

The multi-frequency high-field electron paramagnetic resonance (HFEPR) was used to study the magnetic properties of malarial pigment hemozoin and its synthetic analogue, beta-hematin. (FeIII-protoporphyrin-IX)2 dimers containing five-coordinate high-spin FeIII, S = 5/2, are the building blocks of these pigments. The fit of EPR spectra that were acquired in an unprecedented wide range of microwave frequencies of 34 and 94 GHz for hemozoin and 27-500 GHz for beta-hematin yielded a complete set of intrinsic spin Hamiltonian parameters: D = +5.85(1) cm-1, E = 0, g perpendicular = 1.95(1), g parallel = 2.00(1). These results point to the existence of largely axial symmetry of the iron environment in the bulk phase of hemozoin and beta-hematin.

Animals↗

PubMed2006

Mn(II) binding by the anthracis repressor from Bacillus anthracis.

The anthracis repressor (AntR) is a manganese-activated transcriptional regulator from Bacillus anthracis and is a member of the diphtheria toxin repressor (DtxR) family of proteins. In this paper, we characterize the Mn(II) binding and protein dimerization state using a combination of continuous wave (cw) and pulsed EPR methods. Equilibrium metal binding experiments showed that AntR binds 2 equivalents of Mn(II) with positive cooperativity and apparent dissociation constants of 210 and 16.6 microM. AntR showed sub-millisecond Mn(II) on-rates as measured using stopped-flow EPR. The kinetics of Mn(II) dissociation, measured by displacement with Zn(II), was biphasic with rate constants of 35.7 and 0.115 s(-1). Variable-temperature parallel and perpendicular mode cw EPR spectra showed no evidence of a spin-exchange interaction, suggesting that the two Mn(II) ions are not forming a binuclear cluster. Finally, size exclusion chromatography and double electron-electron resonance EPR demonstrated that AntR forms a dimer in the absence of Mn(II). These results provide insights into the metal activation of AntR and allow a comparison with related DtxR proteins.

Bacillus anthracis↗

PubMed2005

Dielectric resonator-based resonant structure for sensitive ESR measurements at high-hydrostatic pressures.

We present a newly developed microwave probe head that accommodates a gasketed sapphire anvil cell (SAC) for performing sensitive electron spin resonance (ESR) measurements under high-hydrostatic pressures. The system was designed around commercially available dielectric resonators (DRs) having the dielectric permittivity of approximately 30. The microwave resonant structure operates in a wide-stretched double-stacked geometry and resonates in the lowest cylindrical quasi TE(011) mode around 9.2 GHz. The most vital parts of the probe's microwave heart were made of plastic materials, thus making the resonant structure transparent to magnetic field modulation at 100 kHz. The overall ESR sensitivity of the probe was demonstrated for a small speck of 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) positioned in the gasket of the SAC, using water as the pressure-transmitting medium. The system was also used for studying pressure-induced changes in spin-relaxation mechanisms of a quasi-1D-conducting polymer, K(1)C(60). For small samples located in the sample hole of the gasket the probe reveals sensitivity that is only approximately 3 times less than that yielded by regular ESR cavities.

Journal Article↗