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Series

2006

Marquette University

Articles 1 - 7 of 7

Full-Text Articles in Physics

Probing The Reaction Mechanism Of The D-Ala-D-Ala Dipeptidase, Vanx, By Using Stopped-Flow Kinetic And Rapid-Freeze Quench Epr Studies On The Co(Ii)-Substituted Enzyme, Megan L. Matthews, Gopalraj Periyannan, Christine E. Hajdin, Tara K. Sidgel, Brian Bennett, Michael W. Crowder Oct 2006

Probing The Reaction Mechanism Of The D-Ala-D-Ala Dipeptidase, Vanx, By Using Stopped-Flow Kinetic And Rapid-Freeze Quench Epr Studies On The Co(Ii)-Substituted Enzyme, Megan L. Matthews, Gopalraj Periyannan, Christine E. Hajdin, Tara K. Sidgel, Brian Bennett, Michael W. Crowder

Physics Faculty Research and Publications

In an effort to probe the reaction mechanism of VanX, the D-ala-D-ala dipeptidase required for high-level vancomycin resistance in bacteria, stopped-flow kinetic and rapid-freeze quench EPR studies were conducted on the Co(II)-substituted enzyme when reacted with d-ala-d-ala. The intensity of the Co(II) ligand field band at 550 nm decreased (ε550 = 140 to 18 M-1 cm-1) when VanX was reacted with substrate, suggesting that the coordination number of the metal increases from 5 to 6 upon substrate binding. The stopped-flow trace was fitted to a kinetic mechanism that suggests the presence of an intermediate whose breakdown …

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Simulating The Maximum Domain Wall Speed In A Magnetic Nanowire, Andrew Kunz Oct 2006

Simulating The Maximum Domain Wall Speed In A Magnetic Nanowire, Andrew Kunz

Physics Faculty Research and Publications

The dynamics of domain wall motion in permalloy nanowires have been simulated utilizing the Landau-Lifshitz-Gilbert (LLG) equation of motion. The simulation results are presented in terms of the domain wall speed for ranges of the Gilbert damping parameter alpha and nanowire width. The maximum domain wall speed is independent of alpha. The speed of the domain wall can be increased by increasing the nanowire width, but this lowers the critical field. For applied fields below the critical field, the wall moves uniformly along the wire and the speed of the wall increases with increases in the driving field. This behavior …

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Mechanistic Studies On The Mononuclear ZnIi-Containing Metallo-Β-Lactamase Imis From Aeromonas Sobria, Narayan Sharma, Christine E. Hajdin, Sowmya Chandrasekar, Brian Bennett, Ke-Wu Yang, Michael W. Crowder Sep 2006

Mechanistic Studies On The Mononuclear ZnIi-Containing Metallo-Β-Lactamase Imis From Aeromonas Sobria, Narayan Sharma, Christine E. Hajdin, Sowmya Chandrasekar, Brian Bennett, Ke-Wu Yang, Michael W. Crowder

Physics Faculty Research and Publications

In an effort to understand the reaction mechanism of a B2 metallo-β-lactamase, steady-state and pre-steady-state kinetic and rapid freeze quench electron paramagnetic resonance (EPR) studies were conducted on ImiS and its reaction with imipenem and meropenem. pH dependence studies revealed no inflection points in the pH range of 5.0−8.5, while proton inventories demonstrated at least 1 rate-limiting proton transfer. Site-directed mutagenesis studies revealed that Lys224 plays a catalytic role in ImiS, while the side chain of Asn233 does not play a role in binding or catalysis. Stopped-flow fluorescence studies on ImiS, which monitor changes in tryptophan fluorescence on the enzyme, …

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Micromagnetic Simulations On The Dependence Of Gilbert Damping On Domain Wall Velocities In Magnetic Nanowires, Andrew Kunz, B. Kastor May 2006

Micromagnetic Simulations On The Dependence Of Gilbert Damping On Domain Wall Velocities In Magnetic Nanowires, Andrew Kunz, B. Kastor

Physics Faculty Research and Publications

he dependence of damping on domain wall motion and velocity in Permalloy nanowires is presented. The domain wall motion in isolated two micron long Permalloy nanowires, with a rectangular cross-section 10 nm thick and 100 nm wide, is simulated using the Landau-Lifshitz Gilbert (LLG) simulation.Interpreting LLG dynamics can be difficult due to the dependence of the results on the Gilbert damping parameter alpha. The Walker model also predicts the critical field and domain wall velocity as a function of alpha. For these combined reasons the dependence of the domain wall speeds on the damping parameter is explored.

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Kinetic And Spectroscopic Characterization Of The E134a- And E134d-Altered Dape-Encoded N-Succinyl-L,L-Diaminopimelic Acid Desuccinylase From Haemophilus Influenzae, Ryan S. Davis, David L. Bienvenue, Sabina I. Swierczek, Danuta M. Gilner, Lakshman Rajagopal, Brian Bennett, Richard C. Holz Mar 2006

Kinetic And Spectroscopic Characterization Of The E134a- And E134d-Altered Dape-Encoded N-Succinyl-L,L-Diaminopimelic Acid Desuccinylase From Haemophilus Influenzae, Ryan S. Davis, David L. Bienvenue, Sabina I. Swierczek, Danuta M. Gilner, Lakshman Rajagopal, Brian Bennett, Richard C. Holz

Physics Faculty Research and Publications

Glutamate-134 (E134) is proposed to act as the general acid/base during the hydrolysis reaction catalyzed by the dapE-encoded N-succinyl-l,l-diaminopimelic acid desuccinylase (DapE) from Haemophilus influenzae. To date, no direct evidence has been reported for the role of E134 during catalytic turnover by DapE. In order to elucidate the catalytic role of E134, altered DapE enzymes were prepared in which E134 was substituted with an alanine and an aspartate residue. The Michaelis constant (K m) does not change upon substitution with aspartate but the rate of the reaction changes drastically in the following order: glutamate (100% …

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Simulated Domain Wall Dynamics In Magnetic Nanowires, Andrew Kunz Jan 2006

Simulated Domain Wall Dynamics In Magnetic Nanowires, Andrew Kunz

Physics Faculty Research and Publications

The simulated domain wall dynamics in rectangular 10 nm thick, 2000 nm long Permalloy wires of varying width is presented. In the absence of an applied field the static domain wall length is found to be linearly dependent to the width of the nanowire. As magnetic fields of increasing strength are applied along the wire’s long axis, the domain wall motion changes from a uniform reversal to a steplike reversal. The onset of the stepping motion leads to a decrease in the domain wall speed. By continuing to increase the field it is possible to decrease the time between steps …

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Sequential Binding Of Cobalt(Ii) To Metallo-Β-Lactamase Ccra, Gopal R. Periyannan, Alison L. Costello, David L. Tierney, Ke-Wu Yang, Brian Bennett, Michael W. Crowder Jan 2006

Sequential Binding Of Cobalt(Ii) To Metallo-Β-Lactamase Ccra, Gopal R. Periyannan, Alison L. Costello, David L. Tierney, Ke-Wu Yang, Brian Bennett, Michael W. Crowder

Physics Faculty Research and Publications

In an effort to probe Co(II) binding to metallo-β-lactamase CcrA, EPR, EXAFS, and 1H NMR studies were conducted on CcrA containing 1 equiv (1-Co(II)-CcrA) and 2 equiv (Co(II)Co(II)-CcrA) of Co(II). The EPR spectra of 1-Co(II)-CcrA and Co(II)Co(II)-CcrA are distinct and indicate 5/6-coordinate Co(II) ions. The EPR spectra also reveal the absence of significant spin-exchange coupling between the Co(II) ions in Co(II)Co(II)-CcrA. EXAFS spectra of 1-Co(II)-CcrA suggest 5/6-coordinate Co(II) with two or more histidine ligands. EXAFS spectra of Co(II)Co(II)-CcrA also indicate 5/6 ligands at a similar average distance to 1-Co(II)-CcrA, including an average of about two histidines per Co(II). 1 …

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