scholarly journals Extreme electric fields power catalysis in the active site of ketosteroid isomerase

Science ◽  
2014 ◽  
Vol 346 (6216) ◽  
pp. 1510-1514 ◽  
Author(s):  
Stephen D. Fried ◽  
Sayan Bagchi ◽  
Steven G. Boxer
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Active Site ◽  
Stark Effect ◽  
Catalytic Effect ◽  
Biomolecular Systems ◽  
Ketosteroid Isomerase ◽  
Rate Determining Step ◽  
Experimental Approaches ◽  
A Charge

Enzymes use protein architecture to impose specific electrostatic fields onto their bound substrates, but the magnitude and catalytic effect of these electric fields have proven difficult to quantify with standard experimental approaches. Using vibrational Stark effect spectroscopy, we found that the active site of the enzyme ketosteroid isomerase (KSI) exerts an extremely large electric field onto the C=O chemical bond that undergoes a charge rearrangement in KSI’s rate-determining step. Moreover, we found that the magnitude of the electric field exerted by the active site strongly correlates with the enzyme’s catalytic rate enhancement, enabling us to quantify the fraction of the catalytic effect that is electrostatic in origin. The measurements described here may help explain the role of electrostatics in many other enzymes and biomolecular systems.

scholarly journals A Preorganized Electric Field Leads to Minimal Geometrical Reorientation in the Catalytic Reaction of Ketosteroid Isomerase

2020 ◽  
Author(s):  
Yufan Wu ◽  
Stephen Fried ◽  
Steven Boxer
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ground State ◽  
Active Site ◽  
Electrostatic Interactions ◽  
Stark Effect ◽  
Structural Changes ◽  
Enzymatic Catalysis ◽  
Ketosteroid Isomerase ◽  
Computational Enzyme Design

<div><p>Electrostatic interactions play a pivotal role in enzymatic catalysis and are increasingly modeled explicitly in computational enzyme design; nevertheless, they are challenging to measure experimentally. Using vibrational Stark effect (VSE) spectroscopy, we have measured electric fields inside the active site of the enzyme ketosteroid isomerase (KSI). These studies have shown that these fields can be unusually large, but it has been unclear to what extent they specifically stabilize the transition state (TS) relative to a ground state (GS). In the following, we use crystallography and computational modeling to show that KSI’s intrinsic electric field is nearly perfectly oriented to stabilize the geometry of its reaction’s TS. Moreover, we find that this electric field adjusts the orientation of its substrate in the ground state so that the substrate needs to only undergo minimal structural changes upon activation to its TS. This work provides evidence that the active site electric field in KSI is preorganized to facilitate catalysis and provides a template for how electrostatic preorganization can be measured in enzymatic systems. <br></p></div>

scholarly journals A Preorganized Electric Field Leads to Minimal Geometrical Reorientation in the Catalytic Reaction of Ketosteroid Isomerase

2020 ◽  
Author(s):  
Yufan Wu ◽  
Stephen Fried ◽  
Steven Boxer
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Ground State ◽  
Active Site ◽  
Electrostatic Interactions ◽  
Stark Effect ◽  
Structural Changes ◽  
Enzymatic Catalysis ◽  
Ketosteroid Isomerase ◽  
Computational Enzyme Design

<div><p>Electrostatic interactions play a pivotal role in enzymatic catalysis and are increasingly modeled explicitly in computational enzyme design; nevertheless, they are challenging to measure experimentally. Using vibrational Stark effect (VSE) spectroscopy, we have measured electric fields inside the active site of the enzyme ketosteroid isomerase (KSI). These studies have shown that these fields can be unusually large, but it has been unclear to what extent they specifically stabilize the transition state (TS) relative to a ground state (GS). In the following, we use crystallography and computational modeling to show that KSI’s intrinsic electric field is nearly perfectly oriented to stabilize the geometry of its reaction’s TS. Moreover, we find that this electric field adjusts the orientation of its substrate in the ground state so that the substrate needs to only undergo minimal structural changes upon activation to its TS. This work provides evidence that the active site electric field in KSI is preorganized to facilitate catalysis and provides a template for how electrostatic preorganization can be measured in enzymatic systems. <br></p></div>

scholarly journals An Ab Initio QM/MM Study of the Electrostatic Contribution to Catalysis in the Active Site of Ketosteroid Isomerase

Molecules ◽  
2018 ◽  
Vol 23 (10) ◽  
pp. 2410 ◽  
Author(s):  
Xianwei Wang ◽  
Xiao He
Keyword(s):  
Electric Field ◽  
Ab Initio ◽  
Active Site ◽  
Md Simulation ◽  
Stark Effect ◽  
Computational Simulation ◽  
Ketosteroid Isomerase ◽  
Correlation Relationship ◽  
Amber Force Field ◽  
Electrostatic Contribution

The electric field in the hydrogen-bond network of the active site of ketosteroid isomerase (KSI) has been experimentally measured using vibrational Stark effect (VSE) spectroscopy, and utilized to study the electrostatic contribution to catalysis. A large gap was found in the electric field between the computational simulation based on the Amber force field and the experimental measurement. In this work, quantum mechanical (QM) calculations of the electric field were performed using an ab initio QM/MM molecular dynamics (MD) simulation and electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method. Our results demonstrate that the QM-derived electric field based on the snapshots from QM/MM MD simulation could give quantitative agreement with the experiment. The accurate calculation of the electric field inside the protein requires both the rigorous sampling of configurations, and a QM description of the electrostatic field. Based on the direct QM calculation of the electric field, we theoretically confirmed that there is a linear correlation relationship between the activation free energy and the electric field in the active site of wild-type KSI and its mutants (namely, D103N, Y16S, and D103L). Our study presents a computational protocol for the accurate simulation of the electric field in the active site of the protein, and provides a theoretical foundation that supports the link between electric fields and enzyme catalysis.

The vibration of electrified water drops

1971 ◽  
Vol 322 (1551) ◽  
pp. 523-534 ◽  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Axial Ratio ◽  
Uniform Electric Field ◽  
Interferometric Technique ◽  
Photographic Analysis ◽  
Wide Range ◽  
Water Drops ◽  
Strength And Deformation ◽  
A Charge

Pressure has been used as the principal parameter in calculations of the fundamental vibrational frequencies of spherical drops of radius R , density ρ, and surface tension T carrying a charge Q or uncharged spheroidal drops of axial ratio a / b situated in a uniform electric field of strength E . Freely vibrating charged drops have a frequency f = f 0 ( 1 - Q 2 /16π R 3 T ) ½ , as shown previously by Rayleigh (1882) using energy considerations; f 0 is the vibrational frequency of non-electrified drops (Rayleigh 1879). The fundamental frequency of an uncharged drop in an electric field will decrease with increasing field strength and deformation a / b and will equal zero when E ( R )/ T ) ½ = 1.625 and a / b = 1.86; these critical values correspond to the disintegration conditions derived by Taylor (1964). An interferometric technique involving a laser confirmed the accuracy of the calculations concerned with charged drops. The vibration of water drops of radius around 2 mm was studied over a wide range of temperatures as they fell through electric fields either by suspending them in a vertical wind tunnel or allowing them to fall between a pair of vertical electrodes. Photographic analysis of the vibrations revealed good agreement between theory and experiment over the entire range of conditions studied even though the larger drops were not accurately spheroidal and the amplitude of the vibrations was large.

scholarly journals Radio emission from polar caps in pulsars

1996 ◽  
Vol 160 ◽  
pp. 181-182
Author(s):  
Jan Kuijpers ◽  
Martin Volwerk
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Resonance Condition ◽  
Linear Acceleration ◽  
Stellar Atmospheres ◽  
Double Layers ◽  
Radio Pulsars ◽  
Polar Caps ◽  
Particle Speed ◽  
A Charge

Radiation from a charge accelerated along its path or Linear Acceleration Emission (LAE) involves a number of subtleties (Pauli 1921; Ginzburg 1970, 1989). Potential interest of the mechanism for astrophysics has been pointed out by Wagoner (1969). Melrose (1978) and Rowe (1995) have studied amplified LAE from time-varying electric fields for radio pulsars. In contrast with the latter work our calculations are for static electric field structures or double layers (DLs) as are thought to occur in magnetospheres of neutron stars. In ordinary stellar atmospheres a LAE maser can operate in non-relativistic DLs (Kuijpers 1990) at a frequencyω≈kDLυ≈ 2π/ttr, and a wave vectorwithkDL= 2π/L(Lis the DL length,υis the particle speed, andttris the transit time of the DL by the particle). The emission process can be considered as scattering of the electrostatic electric field on fast electrons into electromagnetic radiation satisfying the resonance condition:, when the frequency of the radiated mode in the frame of the emitting electron equals the Doppler shifted frequency of the electric field of the DL (DL wave frequencyωDL≈ 0). For relativistic DLs, as are applicable to pulsar magnetospheres, the emission is expected to be beamed under an angleθ≈γ−1and the frequency of emission boosted (ω≈kDLυ(1 −υcosθ/c)−1≈γ2kDLυ).

scholarly journals Supramolecular Stark Effect in Host-Guest Complexes via Charge Density Analysis

2014 ◽  
Vol 70 (a1) ◽  
pp. C674-C674
Author(s):  
Sajesh Thomas ◽  
Rebecca Fuller ◽  
Alexandre Sobolev ◽  
Philip Schauer ◽  
Simon Grabowsky ◽  
...  
Keyword(s):  
Electric Field ◽  
Charge Density ◽  
Electric Fields ◽  
Active Sites ◽  
Stark Effect ◽  
Dipole Moments ◽  
Covalent Bonds ◽  
Guest Molecules ◽  
Density Mapping ◽  
Density Analysis

The effect of an electric field on the vibrational spectra, the Vibrational Stark Effect (VSE), has been utilized extensively to probe the local electric field in the active sites of enzymes [1, 2]. For this reason, the electric field and consequent polarization effects induced by a supramolecular host system upon its guest molecules attain special interest due to the implications for various biological processes. Although the host-guest chemistry of crown ether complexes and clathrates is of fundamental importance in supramolecular chemistry, many of these multicomponent systems have yet to be explored in detail using modern techniques [3]. In this direction, the electrostatic features associated with the host-guest interactions in the inclusion complexes of halogenated acetonitriles and formamide with 18-crown-6 host molecules have been analyzed in terms of their experimental charge density distribution. The charge density models provide estimates of the molecular dipole moment enhancements which correlate with the simulated values of dipole moments under electric field. The accurate electron density mapping using the multipole formalism also enable the estimation of the electric field experienced by the guest molecules. The electric field vectors thus obtained were utilized to estimate the vibrational stark effect in the nitrile (-C≡N) and carbonyl (C=O) stretching frequencies of the guest molecules via quantum chemical calculations in gas phase. The results of these calculations indicate remarkable elongation of C≡N and C=O bonds due to the electric fields. The electronic polarization in these covalent bonds induced by the field manifests as notable red shifts in their characteristic vibrational frequencies. These results derived from the charge densities are further supported by FT-IR experiments and thus establish the significance of a phenomenon that could be termed as the "supramolecular Stark effect" in crystal environment.

scholarly journals Photo- and electroluminescence of oxide-nitride-oxide-silicon structures for silicon-based optoelectronics

2018 ◽  
Vol 62 (5) ◽  
pp. 546-554
Author(s):  
I. A. Romanov ◽  
L. A. Vlasukova ◽  
F. F. Komarov ◽  
I. N. Parkhomenko ◽  
N. S. Kovalchuk ◽  
...  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Silicon Oxide ◽  
Light Emission ◽  
Chemical Vapor ◽  
Nitride Layer ◽  
Silicon Oxynitride ◽  
Radiative Relaxation ◽  
A Charge ◽  
Nitride Oxide

Oxide-nitride-oxide-silicon (SiO2/SiN0.9/SiO2/Si) structures have been fabricated by chemical vapor deposition. The elemental composition and light emission properties of “SiO2/SiN0.9/SiO2/Si” structures have been studied using Rutherford backscattering spectroscopy (RBS), photo- and electroluminescence (Pl, El). The RBS measurements has shown the presence of an intermediate silicon oxynitride layers at the SiO2–SiN0.9 interfaces.It has been shown that the photoluminescence of the SiO2/SiN0.9/SiO2/Si structure is due to the emission of a SiN0.9 layer, and the electroluminescence is attributed to the emission of silicon oxide and oxynitride layers. A broad intense band with a maximum at 1.9 eV dominates the Pl spectrum. This band attributed to the radiative recombination of excited carriers between the band tail states of the SiN0.9 layer. The origin of the less intense Pl band at 2.8 eV is associated with the presence  of nitrogen defects in the silicon nitride.El was excited in the electrolyte-dielectric-semiconductor system. The electric field strength in the SiO2 layers reached 7–8 MV/cm and exceeded this parameter in nitride layer nearly four times. The electrons accelerating in electric field of 7–8 MV/cm could heat up to energies more than 5 eV. It is sufficient for the excitation of luminescence centres in the silicon oxide and oxynitride layers. The SiO2/SiN0.9/SiO2/Si composition El bands with quantum energies of 1.9 and 2.3 eV are related to the presence of silanol groups (Si–OH) and three-coordinated silicon atoms (≡Si•) in the silicon oxide layers. The El band with an energy of 2.7 eV is attributed to the radiative relaxation of silylene (O2=Si:) centers in the silicon oxynitride regions. It is observed the least reduction of this band intensity under the influence of strong electric fields after a charge flow  of 1–3 C/cm2.

Intersubband Transitions in Asymmetric Quantum Wells with External Electric Field

2014 ◽  
Vol 525 ◽  
pp. 170-176
Author(s):  
Zhao Xu Liu ◽  
Jun Zhu ◽  
Si Hua Ha
Keyword(s):  
Electric Field ◽  
Quantum Wells ◽  
External Electric Field ◽  
Electric Fields ◽  
Stark Effect ◽  
Energy Levels ◽  
Intersubband Transitions ◽  
External Electric Fields ◽  
Asymmetric Quantum ◽  
Negative Field

The quantum-confined Stark effect on the optical absorption of intersubband transitions in an asymmetric AlxGa1-xN/In0.3Ga0.7N/GaN quantum wells is investigated by means of the density matrix formulism. The built-in electric field generated by the piezoelectric and spontaneous polarizations competing against to the external electric fields is considered. As the result, the influences of the built-in and external electric fields on the energy potentials and the eigen stares are discussed in detail. When the positive external electric field is applied, the peak values of the absorption coefficients from 3-2, 2-1 and 3-1 transitions are reduced and moved to the lower photon energy levels. With the negative field, the exactly opposite results can be obtained. Moreover, it is indicated that the results of the wavelengths from the 3-2, 2-1 and 3-1 transitions are reduced by the positive external electric field and increased by the negative field.

Cotton as an Electret

1977 ◽  
Vol 47 (7) ◽  
pp. 471-476 ◽  
Author(s):  
Louis C. Weiss ◽  
Devron P. Thibodeaux
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Elevated Temperatures ◽  
Cotton Fibers ◽  
Threshold Values ◽  
Charge Density Distribution ◽  
Polyester Fibers ◽  
A Charge ◽  
Temperature Time

Research to enhance the storage of electrical charge in lint cotton led to imparting electret-like properties to cotton fibers. An electrostatic field introduced stored, oriented charges within a bundle of cotton fibers. The threshold values of temperature, time, and electric field for production of cotton electrets are defined, and specifications for measuring charge-density distribution are presented. The electret nature of the phenomenon is substantiated by findings that cotton fibers exposed to electric fields at elevated temperatures show long-term, charge-retention properties that are enhanced by short-circuiting. These fibers also display a tendency to a charge-polarity reversal after being removed from the electric field. Furthermore, the waxes native to the single fiber seem to be the basis of this new cotton property. These waxes are related to one of the best known electret materials—carnauba wax. A similar effect with analogous characteristics has also been produced in polyester fibers. With both fibers the effect is less than that possessed by ideal electrets.

Sign in / Sign up

Export Citation Format

Share Document