328 research outputs found
Optical Band Splitting and Electronic Perturbations of the Heme Chromophore in Cytochrome c at Room Temperature Probed by Visible Electronic Circular Dichroism Spectroscopy
AbstractWe have measured the electronic circular dichroism (ECD) of the ferri- and ferro-states of several natural cytochrome c derivatives (horse heart, chicken, bovine, and yeast) and the Y67F mutant of yeast in the region between 300 and 750nm. Thus, we recorded the ECD of the B- and Q-band region as well as the charge-transfer band at âŒ695nm. The B-band region of the ferri-state displays a nearly symmetric couplet at the B0-position that overlaps with a couplet 790cmâ1 higher in energy, which we assigned to a vibronic side-band transition. For the ferro-state, the couplet is greatly reduced, but still detectable. The B-band region is dominated by a positive Cotton effect at energies lower than B0 that is attributed to a magnetically allowed ironâheme charge-transfer transition as earlier observed for nitrosyl myoglobin and hemoglobin. The Q-band region of the ferri-state is poorly resolved, but displays a pronounced positive signal at higher wavenumbers. This must result from a magnetically allowed transition, possibly from the methionine ligand to the dxy-hole of Fe3+. For the ferro-state, the spectra resolve the vibronic structure of the Qv-band. A more detailed spectral analysis reveals that the positively biased spectrum can be understood as a superposition of asymmetric couplets of split Q0 and Qv-states. Substantial qualitative and quantitative differences between the respective B-state and Q-state ECD spectra of yeast and horse heart cytochrome c can clearly be attributed to the reduced band splitting in the former, which results from a less heterogeneous internal electric field. Finally, we investigated the charge-transfer band at 695nm in the ferri-state spectrum and found that it is composed of at least three bands, which are assignable to different taxonomic substates. The respective subbands differ somewhat with respect to their Kuhn anisotropy ratio and their intensity ratios are different for horse and yeast cytochrome c. Our data therefore suggests different substate populations for these proteins, which is most likely assignable to a structural heterogeneity of the distal Fe-M80 coordination of the heme chromophore
Mastering your Fellowship
The series, âMastering your Fellowshipâ, provides examples of the question format encountered in the written examination, Part A of the FCFP(SA) examination. The series aims to help Family Medicine registrars prepare for this examination. Model answers are available online.Keywords: FCFP(SA) examination, Family Medicine registrar
Diffusion and Binding of Radio-Labeled Antibodies in a Tumor
With the decreasing cost of monoclonal antibody production, radioimmunotherapy (RIT) has rapidly emerged as one of the more promising methods of treating cancer cells. RIT makes use of radio-labeled monoclonal antibodies to detect and deliver controlled doses of radiation to malignant cells. The primary advantage of this method is that damage to normal, healthy tissue is minimized. We investigated the use of radio-labeled antibodies as a method of tumor destruction. Our primary interests were the rate of antibody diffusion into the tumor, the antibody binding kinetics, and the overall effectiveness of radioimmunotherapy given the rate of radioactive decay. By modeling the concentration of bound antibody with respect to time, we were able to optimize tumor destruction while minimizing the damage to the surrounding tissue. Our results show that a computer simulation using FIDAP is a time-saving, cost-effective method of obtaining quantitative results about the binding kinetics of antibody to tumor. In addition, we determined that while the binding specificity plays an important role in ensuring proper binding to the tumor, the rate of antibody to antigen complex formation does not affect the treatment and that this process is limited by diffusion. Given this fact, we recommend that low molecular weight antibodies be used because they will typically have higher diffusivities. In an example case of metastatic melanoma, we found that 4.33 mg of 188Re-6D2 complex would destroy the tumor in our model
MARTE based design approach for targeting Reconfigurable Architectures
International audienceThis paper demonstrates the use of a model driven design flow for Multiprocessor System on chips (MPSoCs) such as those dedicated to intensive signal processing applications. Due to the continuous exponential rise in SoC's design complexity, there is a critical need to find new seamless methodologies and tools to handle the SoC co-design aspects. This paper addresses this issue and proposes a novel SoC codesign methodology based on Model Driven Engineering (MDE) and the MARTE (Modeling and Analysis of Real-Time and Embedded Systems) standard proposed by OMG (Object Management Group), in order to raise the design abstraction levels. Extensions of this standard have enabled us to move from high level specifications to execution platforms such as reconfigurable FPGAs
Loan and nonloan flows in the Australian interbank network
High-value transactions between Australian banks are settled in the Reserve
Bank Information and Transfer System (RITS) administered by the Reserve Bank of
Australia. RITS operates on a real-time gross settlement (RTGS) basis and
settles payments sourced from the SWIFT, the Austraclear, and the interbank
transactions entered directly into RITS. In this paper, we analyse a dataset
received from the Reserve Bank of Australia that includes all interbank
transactions settled in RITS on an RTGS basis during five consecutive weekdays
from 19 February 2007 inclusive, a week of relatively quiescent market
conditions. The source, destination, and value of each transaction are known,
which allows us to separate overnight loans from other transactions (nonloans)
and reconstruct monetary flows between banks for every day in our sample. We
conduct a novel analysis of the flow stability and examine the connection
between loan and nonloan flows. Our aim is to understand the underlying causal
mechanism connecting loan and nonloan flows. We find that the imbalances in the
banks' exchange settlement funds resulting from the daily flows of nonloan
transactions are almost exactly counterbalanced by the flows of overnight
loans. The correlation coefficient between loan and nonloan imbalances is about
-0.9 on most days. Some flows that persist over two consecutive days can be
highly variable, but overall the flows are moderately stable in value. The
nonloan network is characterised by a large fraction of persistent flows,
whereas only half of the flows persist over any two consecutive days in the
loan network. Moreover, we observe an unusual degree of coherence between
persistent loan flow values on Tuesday and Wednesday. We probe static
topological properties of the Australian interbank network and find them
consistent with those observed in other countries
Asymmetric band profile of the Soret band of deoxymyoglobin is caused by electronic and vibronic perturbations of the heme group rather than by a doming deformation
Journal of Chemical Physics, 127(13): pp. 135103We measured the Soret band of deoxymyoglobin deoxyMb , myoglobin cyanide MbCN , and
aquo-metmyoglobin all from horse heart with absorption and circular dichroism CD
spectroscopies. A clear non-coincidence was observed between the absorption and CD profiles of
deoxyMb and MbCN, with the CD profiles red- and blueshifted with respect to the absorption band
position, respectively. On the contrary, the CD and absorption profiles of aquametMb were nearly
identical. The observed noncoincidence indicates a splitting of the excited B state due to
heme-protein interactions. CD and absorption profiles of deoxyMb and MbCN were
self-consistently analyzed by employing a perturbation approach for weak vibronic coupling as well
as the relative intensities and depolarization ratios of seven bands in the respective resonance Raman
spectra measured with B-band excitation. The respective By component was found to dominate the
observed Cotton effect of both myoglobin derivatives. The different signs of the noncoincidences
between CD and absorption bands observed for deoxyMb and MbCN are due to different signs of
the respective matrix elements of A1g electronic interstate coupling, which reflects an imbalance of
Goutermanâs 50:50 states. The splitting of the B band reflects contributions from electronic and
vibronic perturbations of B1g symmetry. The results of our analysis suggest that the broad and
asymmetric absorption band of deoxyMb results from this band splitting rather than from its
dependence on heme doming. Thus, we are able to explain recent findings that the temperature
dependences of CO rebinding to myoglobin and the Soret band profile are uncorrelated
Ormos et al., Proc. Natl. Acad. Sci U.S.A. 95, 6762 1998
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