Defining Resonance Raman Spectral Responses to Substrate Binding by Cytochrome P450 from \u3cem\u3ePseudomonas putida\u3c/em\u3e

Resonance Raman spectra are reported for substrate-free and camphor-bound cytochrome P450cam and its isotopically labeled analogues that have been reconstituted with protoheme derivatives that bear -CD3 groups at the 1, 3, 5, and 8-positions (d12-protoheme) or deuterated methine carbons (d4-protoheme). In agreement with previous studies of this and similar enzymes, substrate binding induces changes in the high frequency and low frequency spectral regions, with the most dramatic effect in the low frequency region being activation of a new mode near 367 cm−1. This substrate-activated mode had been previously assigned as a second “propionate bending” mode (Chen et al., Biochemistry, 2004, 43, 1798–1808), arising in addition to the single propionate bending mode observed for the substrate-free form at 380 cm−1. In this work, this newly activated mode is observed to shift by 8 cm−1 to lower frequency in the d12-protoheme reconstituted enzyme (i.e., the same shift as that observed for the higher frequency “propionate bending” mode) and is therefore consistent with the suggested assignment. However, the newly acquired data for the d4-protoheme substituted analogue also support an earlier alternate suggestion (Deng et al., Biochemistry, 1999, 38, 13699–13706) that substrate binding activates several heme out-of-plane modes, one of which (γ6) is accidentally degenerate with the 367 cm−1 propionate bending mode. Finally, the study of the enzyme reconstituted with the protoheme-d4, which shifts the macrocycle ν10 mode, has now allowed a definitive identification of the vinyl CC stretching modes

The Integrated Spectra of M32 and of 47 Tucanae: A Comparative Study in the Mid-Ultraviolet With IUE

Low-resolution mid-UV spectra of M32 and 47 Tuc have been extracted from the IUE archival database, along with spectra of 41 F and G dwarfs with well-determined atmospheric parameters and integrated spectra of 24 Galactic globular clusters. We have used five mid-UV spectral indices defined by Fanelli et al. to constrain the stellar content of M32 and 47 Tuc and to make a comparative study between the two stellar systems. In the case of 47 Tuc, the bulk of the mid-UV light is shown to come from the main-sequence turnoff stars, with much smaller (but significant) contributions coming from red horizontal-branch stars, red giants, and A stars (presumably, blue stragglers). In contrast, M32 is shown to have no significant contribution from a red horizontal-branch population, has a more metal-rich main-sequence turnoff, and has a significantly larger hot star contribution than is inferred to be present in 47 Tuc. These inferences are consistent with conclusions obtained from integrated light studies of M32 and 47 Tuc in the blue

Limitations of the Standard Gravitational Perfect Fluid Paradigm

We show that the standard perfect fluid paradigm is not necessarily a valid description of a curved space steady state gravitational source. Simply by virtue of not being flat, curved space geometries have to possess intrinsic length scales, and such length scales can affect the fluid structure. For modes of wavelength of order or greater than such scales eikonalized geometrical optics cannot apply and rays are not geodesic. Covariantizing thus entails not only the replacing of flat space functions by covariant ones, but also the introduction of intrinsic scales that were absent in flat space. In principle it is thus unreliable to construct the curved space energy-momentum tensor as the covariant generalization of a geodesic-based flat spacetime energy-momentum tensor. By constructing the partition function as an incoherent average over a complete set of modes of a scalar field propagating in a curved space background, we show that for the specific case of a static, spherically symmetric geometry, the steady state energy-momentum tensor that ensues will in general be of the form $T_{\mu\nu}=(\rho+p)U_{\mu}U_{\nu}+pg_{\mu\nu}+\pi_{\mu\nu}$ where the anisotropic $\pi_{\mu\nu}$ is a symmetric, traceless rank two tensor which obeys $U^{\mu}\pi_{\mu\nu}=0$. Such a $\pi_{\mu\nu}$ type term is absent for an incoherently averaged steady state fluid in a spacetime where there are no intrinsic length scales, and in principle would thus be missed in a covariantizing of a flat spacetime $T_{\mu\nu}$. While the significance of such $\pi_{\mu\nu}$ type terms would need to be evaluated on a case by case basis, through the use of kinetic theory we reassuringly find that the effect of such $\pi_{\mu\nu}$ type terms is small for weak gravity stars where perfect fluid sources are commonly used.Comment: Final version to appear in General Relativity and Gravitation (the final publication is available at http://www.springerlink.com). 29 pages, 1 figur

China's Local Comparative Advantage

China's trade pattern is influenced not just by its overall comparative advantage in labor intensive goods but also by geography. We use two variants of the Eaton-Kortum (2002) model to study China's local comparative advantage. The theory predicts that China's share of export markets should grow most rapidly where China's share is initially large. A corollary is that exporters that have a big market share where China's share is initially large should see the largest fall in their market shares. These market share change predictions are strongly supported in the data from 1996 to 2006. We also show theoretically that since trade costs are proportional to weight rather than value, relative distance affects local comparative advantage as well as the overall volume of trade. The model predicts that China has a comparative advantage in heavy goods in nearby markets, and lighter goods in more distant markets. This theory motivates a simple empirical prediction: within a product, China's export unit values should be increasing in distance. We find strong support for this effect in our empirical analysis on product-level Chinese exports in 2006.

Quantification of uf and pf Resins in MDF Fiber with an X-Ray Fluorescence Spectrometer

This article describes methods to quantify urea-formaldehyde (UF) resin and phenol-formaldehyde (PF) resin contents in medium density fiberboard (MDF) using a wavelength dispersive X-ray fluorescence spectrometer (WDXRF). The methods are based on the principle that a specific metallic element shows its characteristic X-ray fluorescence spectrum, the intensity of which is correlated quantitatively to its concentration. In the case of UF-blended MDF fiber, 2.4% copper sulfate pentahydrate CuSO4.5H2O (based on resin solids) was premixed with the resin as a labeling agent. Quantification of copper ion was performed using XRF. Based on calibrations with laboratory-prepared standard fiber samples of known UF resin and copper quantities, the results of XRF measurements were converted to resin loading rates. In the case of PF-blended fiber, the PF resin contents in the MDF fiber samples were successfully quantified by measuring the existing sodium ion Na+ in the resol resin with XRF. Linear calibration curves between fluorescence intensity of copper or sodium and resin content were established respectively for UF and PF resins. Test results show that the methods were precise and reliable

Searching for Hydrogen in Type Ib Supernovae

We present synthetic spectral fits of the typical Type Ib SN 1999dn and the Hydrogen Rich Ib SN 2000H using the generalized non-local thermodynamic equilibrium stellar atmospheres code \phx. We fit model spectra to five epochs of SN 1999dn ranging from ten days pre-maximum light to 17 days post-maximum light and the two earliest epochs of SN 2000H available, maximum light and six days post-maximum. Our goal is to investigate the possibility of hydrogen in Type Ib Supernovae (SNe Ib), specifically a feature around 6200\AA\ which has previously been attributed to high velocity H-alpha. In earlier work on SN 1999dn we found the most plausible alternative to H-alpha to be a blend of Si II and Fe II lines which can be adjusted to fit by increasing the metallicity. Our models are simple; they assume a powerlaw density profile with radius, homologous expansion, and solar compositions. The helium core is produced by burning 4H --> He in order to conserve nucleon number. For models with hydrogen the outer skin of the model consists of a shell of solar composition. The hydrogen mass of the standard solar composition shell is M_H less than about 0.001 times the mass of the sun in SN 1999dn and M_H less than about 0.2 times the mass of the sun for SN 2000H. Our models fit the observed spectra reasonably well, successfully reproducing most features including the characteristic He I absorptions. The hydrogen feature in SN 1999dn is clear, but much more pronounced in SN 2000H. We discuss a possible evolutionary scenario that accounts for the dichotomy in the hydrogen shell mass between these two supernovae.Comment: 20 pages, 11 figures, ApJ, in pres