574 research outputs found
The Riemann Surface of a Static Dispersion Model and Regge Trajectories
The S-matrix in the static limit of a dispersion relation is a matrix of a
finite order N of meromorphic functions of energy in the plane with
cuts . In the elastic case it reduces to N functions
connected by the crossing symmetry matrix A. The scattering of
a neutral pseodoscalar meson with an arbitrary angular momentum l at a source
with spin 1/2 is considered (N=2). The Regge trajectories of this model are
explicitly found.Comment: 5 pages, LaTe
MmpL3 is the flippase for mycolic acids in mycobacteria
The defining feature of the mycobacterial outer membrane (OM) is the presence of mycolic acids (MAs), which, in part, render the bilayer extremely hydrophobic and impermeable to external insults, including many antibiotics. Although the biosynthetic pathway of MAs is well studied, the mechanism(s) by which these lipids are transported across the cell envelope is(are) much less known. Mycobacterial membrane protein Large 3 (MmpL3), an essential inner membrane (IM) protein, is implicated in MA transport, but its exact function has not been elucidated. It is believed to be the cellular target of several antimycobacterial compounds; however,
evidence for direct inhibition of MmpL3 activity is also lacking. Here, we establish that MmpL3 is the MA flippase at the IM of mycobacteria and is the molecular target of BM212, a 1,5-diarylpyrrole compound. We develop assays that selectively access mycolates on the surface of Mycobacterium smegmatis spheroplasts, allowing us to monitor flipping of MAs across the IM. Using these assays, we establish the mechanism of action of BM212 as a potent MmpL3 inhibitor, and use it as a molecular probe to demonstrate the requirement for functional MmpL3 in the transport of MAs across the IM. Finally,we showthat BM212 bindsMmpL3 directly and inhibits its activity. Our work provides fundamental insights into OM biogenesis and MA transport in mycobacteria. Furthermore, our assays serve as an important platform for accelerating the validation of small molecules that target MmpL3, and their development as future antituberculosis drugs
Axial anomaly and the interplay of quark loops with pseudoscalar and vector mesons in the gamma* --> pi+ pi0 pi- process
Motivated by the ongoing measurements of the Primakoff process pi- gamma* -->
pi- pi0 by COMPASS collaboration at CERN, the transition form factor for the
canonical anomalous process gamma* --> pi+ pi0 pi- is calculated in a
constituent quark loop model. The simplest contribution to this process is the
quark "box" amplitude. In the present paper we also explicitly include the
vector meson degrees of freedom, i.e., the rho and the omega, thus giving rise
to additional, resonant contributions. We find that in order to satisfy the
axial anomaly result, a further subtraction in the resonant part is needed. The
results are then compared with the vector meson dominance model as well as the
Dyson--Schwinger calculations, the chiral perturbation theory result, and the
available data.Comment: 21 pages, 8 eps figures, revtex4, a factor of 2 in resonant
contribution corrected, three figures revised and one added, discussion
enlarged and references adde
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