1,398 research outputs found
Cytochemical studies of planetary microorganisms - Explorations in exobiology Status report, 1 Apr. - 1 Oct. 1967
Molecular research instrumentation for exobiological studie
Cytochemical studies of planetary microorganisms - Explorations in exobiology Status report, Sep. 1, 1965 - Apr. 1, 1966
Cytochemical studies of planetary microorganisms by fluorometry, gas chromatography and optical resolution, mass spectrometry, computer managed instrumentation, and UV microspectrometr
Relationship of planetary quarantine to biological search strategy
Decision theory biological search strategies and planetary quarantine aspects of Mars exploratory mission
A Criterion That Determines Fast Folding of Proteins: A Model Study
We consider the statistical mechanics of a full set of two-dimensional
protein-like heteropolymers, whose thermodynamics is characterized by the
coil-to-globular () and the folding () transition temperatures.
For our model, the typical time scale for reaching the unique native
conformation is shown to scale as , where
, is the number of residues, and scales
algebraically with . We argue that scales linearly with the inverse of
entropy of low energy non-native states, whereas is almost
independent of it. As , non-productive intermediates
decrease, and the initial rapid collapse of the protein leads to structures
resembling the native state. Based solely on {\it accessible} information,
can be used to predict sequences that fold rapidly.Comment: 10 pages, latex, figures upon reques
A Multicanonical Molecular Dynamics Study on a Simple Bead-Spring Model for Protein Folding
We have performed a multicanonical molecular dynamics simulation on a simple
model protein.We have studied a model protein composed of charged, hydrophobic,
and neutral spherical bead monomers.Since the hydrophobic interaction is
considered to significantly affect protein folding, we particularly focus on
the competition between effects of the Coulomb interaction and the hydrophobic
interaction. We found that the transition which occurs upon decreasing the
temperature is markedly affected by the change in both parameters and forms of
the hydrophobic potential function, and the transition changes from first order
to second order, when the Coulomb interaction becomes weaker.Comment: 7 pages, 6 postscript figures, To appear in J.Phys.Soc.Jpn. Vol.70
No.
The effect of local thermal fluctuations on the folding kinetics: a study from the perspective of the nonextensive statistical mechanics
Protein folding is a universal process, very fast and accurate, which works
consistently (as it should be) in a wide range of physiological conditions. The
present work is based on three premises, namely: () folding reaction is a
process with two consecutive and independent stages, namely the search
mechanism and the overall productive stabilization; () the folding kinetics
results from a mechanism as fast as can be; and () at nanoscale
dimensions, local thermal fluctuations may have important role on the folding
kinetics. Here the first stage of folding process (search mechanism) is focused
exclusively. The effects and consequences of local thermal fluctuations on the
configurational kinetics, treated here in the context of non extensive
statistical mechanics, is analyzed in detail through the dependence of the
characteristic time of folding () on the temperature and on the
nonextensive parameter .The model used consists of effective residues
forming a chain of 27 beads, which occupy different sites of a D infinite
lattice, representing a single protein chain in solution. The configurational
evolution, treated by Monte Carlo simulation, is driven mainly by the change in
free energy of transfer between consecutive configurations. ...Comment: 19 pages, 3 figures, 1 tabl
Directed transport as a mechanism for protein folding in vivo
We propose a model for protein folding in vivo based on a Brownian-ratchet
mechanism in the multidimensional energy landscape space. The device is able to
produce directed transport taking advantage of the assumed intrinsic asymmetric
properties of the proteins and employing the consumption of energy provided by
an external source. Through such a directed transport phenomenon, the
polypeptide finds the native state starting from any initial state in the
energy landscape with great efficacy and robustness, even in the presence of
different type of obstacles. This model solves Levinthal's paradox without
requiring biased transition probabilities but at the expense of opening the
system to an external field.Comment: 16 pages, 7 figure
Reply to Comment on "Criterion that Determines the Foldability of Proteins"
We point out that the correlation between folding times and in protein-like heteropolymer models where
and are the collapse and folding transition temperatures
was already established in 1993 before the other presumed equivalent criterion
(folding times correlating with alone) was suggested. We argue that the
folding times for these models show no useful correlation with the energy gap
even if restricted to the ensemble of compact structures as suggested by
Karplus and Shakhnovich (cond-mat/9606037).Comment: 6 pages, Latex, 2 Postscript figures. Plots explicitly showing the
lack of correlation between folding time and energy gap are adde
Sequence Dependence of Self-Interacting Random Chains
We study the thermodynamic behavior of the random chain model proposed by
Iori, Marinari and Parisi, and how this depends on the actual sequence of
interactions along the chain. The properties of randomly chosen sequences are
compared to those of designed ones, obtained through a simulated annealing
procedure in sequence space. We show that the transition to the folded phase
takes place at a smaller strength of the quenched disorder for designed
sequences. As a result, folding can be relatively fast for these sequences.Comment: 14 pages, uuencoded compressed postscript fil
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