1,607 research outputs found
Inactivation of Mandelate Racemase by 3-Hydroxypyruvate Reveals a Potential Mechanistic Link between Enzyme Superfamilies
Mandelate racemase (MR), a member of the enolase superfamily, catalyzes the Mg2+-dependent interconversion of the enantiomers of mandelate. Several α-keto acids are modest competitive inhibitors of MR [e.g., mesoxalate (Ki = 1.8 ± 0.3 mM) and 3-fluoropyruvate (Ki = 1.3 ± 0.1 mM)], but, surprisingly, 3-hydroxypyruvate (3-HP) is an irreversible, time-dependent inhibitor (kinact/KI = 83 ± 8 M–1 s–1). Protection from inactivation by the competitive inhibitor benzohydroxamate, trypsinolysis and electrospray ionization tandem mass spectrometry analyses, and X-ray crystallographic studies reveal that 3-HP undergoes Schiff-base formation with Lys 166 at the active site, followed by formation of an aldehyde/enol(ate) adduct. Such a reaction is unprecedented in the enolase superfamily and may be a relic of an activity possessed by a promiscuous progenitor enzyme. The ability of MR to form and deprotonate a Schiff-base intermediate furnishes a previously unrecognized mechanistic link to other α/β-barrel enzymes utilizing Schiff-base chemistry and is in accord with the sequence- and structure-based hypothesis that members of the metal-dependent enolase superfamily and the Schiff-base-forming N-acetylneuraminate lyase superfamily and aldolases share a common ancestor
The influence of magnesium and oxalic acid upon the absorption and retention of calcium and phosphorus
The present work was undertaken to study the effect of excess of magnesium and oxalic acid on calcium-phosphorus utilization, retention and excretion when added to a normal balanced ration fed to lambs
Passive Sliders on Fluctuating Surfaces: Strong-Clustering States
We study the clustering properties of particles sliding downwards on a
fluctuating surface evolving through the Kardar-Parisi-Zhang equation, a
problem equivalent to passive scalars driven by a Burgers fluid. Monte Carlo
simulations on a discrete version of the problem in one dimension reveal that
particles cluster very strongly: the two point density correlation function
scales with the system size with a scaling function which diverges at small
argument. Analytic results are obtained for the Sinai problem of random walkers
in a quenched random landscape. This equilibrium system too has a singular
scaling function which agrees remarkably with that for advected particles.Comment: To be published in Physical Review Letter
Synthesis and Properties of N-Bromosuccinimide Derivatives of Ammonium Dialkyl/Alkylene Dithiophosphates
Reaction of N-bromosuccinimide with ammonium salt of alkylene (dialkyl) dithiophosphates, [OGOPS(2)NH(4); G=−CMe(2)CMe(2)−CH(2)CMe(2)CH(2)−, CMe(2)CH(2)CHMe(2)−, CH(2)CH(2)CHMe(2)−; (RO)(2)PS(2)NH(4); R=C(2)H(5), n−C(3)H(7), i−C(3)H(7)], in 1 : 1 molor ratio in refluxing benzene solution yields red/brown-colored sticky liquids. These newly synthesized complexes have been characterised by physicochemical and spectroscopic techniques (MW, IR, NMR [(1)H and (31)P]). The computational semiempirical calculations (MOPAC6P/c) have also been studied for these complexes. On the basis of the above studies, the formation of P−S−N chemical linkage has been established
Gigahertz-Peaked Spectrum Radio Sources in Nearby Galaxies
There is now strong evidence that many low-luminosity AGNs (LLAGNs) contain
accreting massive black holes and that the nuclear radio emission is dominated
by parsec-scale jets launched by these black holes. Here, we present
preliminary results on the 1.4 GHz to 667 GHz spectral shape of a well-defined
sample of 16 LLAGNs. The LLAGNs have a falling spectrum at high GHz
frequencies. Several also show a low-frequency turnover with a peak in the 1-20
GHz range. The results provide further support for jet dominance of the core
radio emission. The LLAGNs show intriguing similarities with gigahertz-peaked
spectrum (GPS) sources.Comment: 6 pages, to appear in ASP Conference series, 2002, Vol. 25
Dynamical vs. Auxiliary Fields in Gravitational Waves around a Black Hole
The auxiliary/dynamic decoupling method of hep-th/0609001 applies to
perturbations of any co-homogeneity 1 background (such as a spherically
symmetric space-time or a homogeneous cosmology). Here it is applied to compute
the perturbations around a Schwarzschild black hole in an arbitrary dimension.
The method provides a clear insight for the existence of master equations. The
computation is straightforward, coincides with previous results of
Regge-Wheeler, Zerilli and Kodama-Ishibashi but does not require any ingenuity
in either the definition of variables or in fixing the gauge. We note that the
method's emergent master fields are canonically conjugate to the standard ones.
In addition, our action approach yields the auxiliary sectors.Comment: 26 page
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