8,084 research outputs found
Ligand binding to a hemoprotein lacking the distal histidine. The myoglobin from aplysia limacina (Val(E7)).
The time course of ligand recombination to the myoglobin from Aplysia limacina, which has Val(E7), was measured following photolysis by flashes of 35 ps to 300 ns with a time resolution of 10 ps or 1 ns. CO shows only biomolecular recombination. O2 has a small geminate reaction with a half-time of tens of picoseconds, but no nanosecond geminate reaction. NO has two picosecond relaxations with half-times of 70 ps (15%) and 1 ns (80%) and one nanosecond relaxation with a half-time of 4.6 ns. The biomolecular rates for O2 and NO are the same: 2 x 10(7) M-1 s-1. Methyl and ethyl isonitriles have a geminate reaction with a half-time of 35 ps. Ethyl isonitrile has, in addition, a nanosecond relaxation (25%) with a half-time of 100 ns. t-Butyl isonitrile has four geminate relaxations (10 ps, 35 ps, 1 ns, and 1 microseconds). Analysis of the results suggests much easier movement of ligand between the heme pocket and the exterior than in sperm whale myoglobin (His(E7]. The reactivity of the heme is little different, placing the effect of the differences from sperm whale myoglobin on the distal side of the heme
Ligand binding and conformation change in the dimeric hemoglobin of the clam Scapharca inaequivalvis.
The reaction with carbon monoxide of the cooperative dimeric hemoglobin from Scapharca inaequivalvis has been examined by flash photolysis. In the nanosecond time range, geminate rebinding of 5% of dissociated CO occurs with a rate constant of 1.4 x 10(7) s-1. There is a change in absorbance of deoxyhemoglobin following photolysis at a rate of 1.2 x 10(6) s-1, consistent with a shift in the position of the Soret band to longer wavelengths. The amplitude of the change is proportional to the population of deoxydimer. In much of the Soret region this change is greater than the absorbance excursion associated with geminate recombination. There is at least one other slower change associated with the singly liganded species. Geminate rebinding of NO has components of 50, 8, and 0.035 ns-1, accounting for 75%, 25%, and less than 1% of the total reaction observed after a 35-ps photolysis flash. Simulation of diffusion of NO by molecular dynamics shows the ligands moving from the heme pocket to a subsidiary space between the edge of the heme and the surface of the protein
Termination dependent topological surface states of the natural superlattice phase BiSe
We describe the topological surface states of BiSe, a compound in the
infinitely adaptive Bi-BiSe natural superlattice phase series,
determined by a combination of experimental and theoretical methods. Two
observable cleavage surfaces, terminating at Bi or Se, are characterized by
angle resolved photoelectron spectroscopy and scanning tunneling microscopy,
and modeled by ab-initio density functional theory calculations. Topological
surface states are observed on both surfaces, but with markedly different
dispersions and Kramers point energies. BiSe therefore represents the
only known compound with different topological states on differently terminated
surfaces.Comment: 5 figures references added Published in PRB:
http://link.aps.org/doi/10.1103/PhysRevB.88.08110
Reproducing kernel potential energy surfaces in biomolecular simulations: Nitric oxide binding to myoglobin
Multidimensional potential energy surfaces based on reproducing kernel-interpolation are employed to explore the energetics and dynamics of free and bound nitric oxide in myoglobin (Mb). Combining a force field description for the majority of degrees of freedom and the higher-accuracy representation for the NO ligand and the Fe out-of-plane motion allows for a simulation approach akin to a mixed quantum mechanics/molecular mechanics treatment. However, the kernel-representation can be evaluated at conventional force-field speed. With the explicit inclusion of the Fe-out-of-plane (Fe-oop) coordinate, the dynamics and structural equilibrium after photodissociation of the ligand are correctly described compared to experiment. Experimentally, the Fe-oop coordinate plays an important role for the ligand dynamics. This is also found here where the isomerization dynamics between the Fe-ON and Fe-NO state is significantly affected whether or not this co-ordinate is explicitly included. Although the Fe-ON conformation is metastable when considering only the bound (2)A state, it may disappear once the (4)A state is included. This explains the absence of the Fe-ON state in previous experimental investigations of MbNO
Lambda flow in heavy-ion collisions: the role of final-state interactions
Lambda flow in Ni+Ni collisions at SIS energies is studied in the
relativistic transport model (RVUU 1.0). It is found that for primordial
lambdas the flow is considerably weaker than proton flow. The inclusion of
final-state interactions, especially the propagation of lambdas in mean-field
potential, brings the lambda flow close to that of protons. An accurate
determination of lambda flow in heavy-ion experiments is shown to be very
useful for studying lambda properties in dense matter.Comment: 14 pages, LaTeX, figures available from [email protected], to appear
in Phys. Rev.
A broken solar type II radio burst induced by a coronal shock propagating across the streamer boundary
We discuss an intriguing type II radio burst that occurred on 2011 March 27.
The dynamic spectrum was featured by a sudden break at about 43 MHz on the
well-observed harmonic branch. Before the break, the spectrum drifted gradually
with a mean rate of about -0.05 MHz/s. Following the break, the spectrum jumped
to lower frequencies. The post-break emission lasted for about three minutes.
It consisted of an overall slow drift which appeared to have a few fast drift
sub-bands. Simultaneous observations from the Solar TErrestrial RElations
Observatory (STEREO) and the Solar Dynamics Observatory (SDO) were also
available and are examined for this event. We suggest that the slow-drift
period before the break was generated inside a streamer by a coronal eruption
driven shock, and the spectral break as well as the relatively wide spectrum
after the break is a consequence of the shock crossing the streamer boundary
where density drops abruptly. It is suggested that this type of radio bursts
can be taken as a unique diagnostic tool for inferring the coronal density
structure, as well as the radio emitting source region.Comment: 12 pages, 5 figures, accepted by ApJ 201
Observed photodetachment in parallel electric and magnetic fields
We investigate photodetachment from negative ions in a homogeneous 1.0-T
magnetic field and a parallel electric field of approximately 10 V/cm. A
theoretical model for detachment in combined fields is presented. Calculations
show that a field of 10 V/cm or more should considerably diminish the Landau
structure in the detachment cross section. The ions are produced and stored in
a Penning ion trap and illuminated by a single-mode dye laser. We present
preliminary results for detachment from S- showing qualitative agreement with
the model. Future directions of the work are also discussed.Comment: Nine pages, five figures, minor revisions showing final publicatio
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