Theorem on the Distribution of Short Time Single Particle Displacements

The distribution of the initial very short-time displacements of a single particle is considered for a class of classical systems with Gaussian initial velocity distributions and arbitrary initial particle positions. A very brief sketch is given of a rather intricate and lengthy proof that for this class of systems the nth order cumulants behave as t^{2n} for all n>2, rather than as t^{n}. We also briefly discuss some physical consequences for liquids.Comment: Short 8 page pedagogical review of cond-mat/0505734 for Proc. of "News, Expectations and Trends in Statistical Physics", Crete 200

Resonance Raman Spectroscopic Studies of Hydroperoxo Derivatives of Cobalt-substituted Myoglobin

Recent progress in generating and stabilizing reactive heme protein enzymatic intermediates by cryoradiolytic reduction has prompted application of a range of spectroscopic approaches to effectively interrogate these species. The impressive potential of resonance Raman spectroscopy for characterizing such samples has been recently demonstrated in a number of studies of peroxo- and hydroperoxo-intermediates. While it is anticipated that this approach can be productively applied to the wide range of heme proteins whose reaction cycles naturally involve these peroxo- and hydroperoxo-intermediates, one limitation that sometimes arises is the lack of enhancement of the key intraligand ν(O–O) stretching mode in the native systems. The present work was undertaken to explore the utility of cobalt substitution to enhance both the ν(Co–O) and ν(O–O) modes of the CoOOH fragments of hydroperoxo forms of heme proteins bearing a trans–axial histidine linkage. Thus, having recently completed RR studies of hydroperoxo myoglobin, attention is now turned to its cobalt-substituted analogue. Spectra are acquired for samples prepared with 16O2 and 18O2 to reveal the ν(M–O) and ν(O–O) modes, the latter indeed being observed only for the cobalt-substituted proteins. In addition, spectra of samples prepared in deuterated solvents were also acquired, providing definitive evidence for the presence of the hydroperoxo-species

Resonance Raman Interrogation of the Consequences of Heme Rotational Disorder in Myoglobin and its Ligated Derivatives

Resonance Raman spectroscopy is employed to characterize heme site structural changes arising from conformational heterogeneity in deoxyMb and ligated derivatives, i.e., the ferrous CO (MbCO) and ferric cyanide (MbCN) complexes. The spectra for the reversed forms of these derivatives have been extracted from the spectra of reconstituted samples. Dramatic changes in the low-frequency spectra are observed, where newly observed RR modes of the reversed forms are assigned using protohemes that are selectively deuterated at the four methyl groups or at the four methine carbons. Interestingly, while substantial changes in the disposition of the peripheral vinyl and propionate groups can be inferred from the dramatic spectral shifts, the bonds to the internal histidyl imidazole ligand and those of the Fe−CO and Fe−CN fragments are not significantly affected by the heme rotation, as judged by lack of significant shifts in the ν(Fe−NHis), ν(Fe−C), and ν(C−O) modes. In fact, the apparent lack of an effect on these key vibrational parameters of the Fe−NHis, Fe−CO, and Fe−CN fragments is entirely consistent with previously reported equilibrium and kinetic studies that document virtually identical functional properties for the native and reversed forms

Using Resonance Raman Cross-section Data to Estimate the Spin State Populations of Cytochromes P450

The cytochromes P450 (CYPs) are heme proteins responsible for the oxidation of xenobiotics and pharmaceuticals and the biosynthesis of essential steroid products. In all cases, substrate binding initiates the enzymatic cycle, converting ferric low-spin to high-spin state, with the efficiency of the conversion varying widely for different substrates, so documentation of this conversion for a given substrate is an important objective. Resonance Raman (rR) spectroscopy can effectively yield distinctive frequencies for the ν3 ‘spin state marker’ bands. Here, employing a reference cytochrome P450 (CYP101), the intensities of the ν3 modes (ILS) and (IHS) relative to an internal standard (sodium sulfate) yield relative populations for the two spin states; i.e., a value of 1.24 was determined for the ratio of the relative cross sections for the ν3 modes. The use of this value was then shown to permit a reliable calculation of relative populations of the two spin states from rR spectra of several other CYPs P450. The importance of this work is that, using this information, it is now possible to conveniently document by rR the spin state population without conducting separate experiments requiring different analytical methods, instrumentation, and additional sample

Resonance Raman Spectroscopy Reveals pH-Dependent Active Site Structural Changes of Lactoperoxidase Compound 0 and Its Ferryl Heme O–O Bond Cleavage Products

The first step in the enzymatic cycle of mammalian peroxidases, including lactoperoxidase (LPO), is binding of hydrogen peroxide to the ferric resting state to form a ferric-hydroperoxo intermediate designated as Compound 0, the residual proton temporarily associating with the distal pocket His109 residue. Upon delivery of this “stored” proton to the hydroperoxo fragment, it rapidly undergoes O–O bond cleavage, thereby thwarting efforts to trap it using rapid mixing methods. Fortunately, as shown herein, both the peroxo and the hydroperoxo (Compound 0) forms of LPO can be trapped by cryoradiolysis, with acquisition of their resonance Raman (rR) spectra now permitting structural characterization of their key Fe–O–O fragments. Studies were conducted under both acidic and alkaline conditions, revealing pH-dependent differences in relative populations of these intermediates. Furthermore, upon annealing, the low pH samples convert to two forms of a ferryl heme O–O bond-cleavage product, whose ν(Fe═O) frequencies reflect substantially different Fe═O bond strengths. In the process of conducting these studies, rR structural characterization of the dioxygen adduct of LPO, commonly called Compound III, has also been completed, demonstrating a substantial difference in the strengths of the Fe–O linkage of the Fe–O–O fragment under acidic and alkaline conditions, an effect most reasonably attributed to a corresponding weakening of the trans-axial histidyl imidazole linkage at lower pH. Collectively, these new results provide important insight into the impact of pH on the disposition of the key Fe–O–O and Fe═O fragments of intermediates that arise in the enzymatic cycles of LPO, other mammalian peroxidases, and related proteins

Twentieth Century Nicaraguan Protest Poetry: The Struggle for Cultural Hegemony

The University of Kansas has long historical connections with Central America and the many Central Americans who have earned graduate degrees at KU. This work is part of the Central American Theses and Dissertations collection in KU ScholarWorks and is being made freely available with permission of the author through the efforts of Professor Emeritus Charles Stansifer of the History department and the staff of the Scholarly Communications program at the University of Kansas Libraries’ Center for Digital Scholarship

Resonance Raman Spectroscopy of the Oxygenated Intermediates of Human CYP19A1 Implicates a Compound I Intermediate in the Final Lyase Step

CYP19A1, or aromatase, a cytochrome P450 responsible for estrogen biosynthesis in humans, is an important therapeutic target for the treatment of breast cancer. There is still controversy surrounding the identity of reaction intermediate that catalyzes carbon–carbon scission in this key enzyme. Probing the oxy-complexes of CYP19A1 poised for hydroxylase and lyase chemistries using resonance Raman spectroscopy and drawing a comparison with CYP17A1, we have found no significant difference in the frequencies or isotopic shifts for these two steps in CYP19A1. Our experiments implicate the involvement of Compound I in the terminal lyase step of CYP19A1 catalysis

Defining the Structural Consequences of Mechanism-Based Inactivation of Mammalian Cytochrome P450 2B4 Using Resonance Raman Spectroscopy

In view of the potent oxidizing strength of cytochrome P450 intermediates, it is not surprising that certain substrates can give rise to reactive species capable of attacking the heme or critical distal-pocket protein residues to irreversibly modify the enzyme in a process known as mechanism-based (MB) inactivation, a result that can have serious physiological consequences leading to adverse drug−drug interactions and toxicity. While methods exist to document the attachment of these substrate fragments, it is more difficult to gain insight into the structural basis for the altered functional properties of these modified enzymes. In response to this pressing need to better understand MB inhibition, we here report the first application of resonance Raman spectroscopy to study the inactivation of a truncated form of mammalian CYP2B4 by the acetylenic inhibitor 4-(tert-butyl)phenylacetylene, whose activated form is known to attach to the distal-pocket T302 residue of CYP2B4