1
|
Hasimoto Y, Sugawa M, Nishiguchi Y, Aeba F, Tagawa A, Suga K, Tanaka N, Ueno H, Yamashita H, Yokota R, Masaike T, Nishizaka T. Direct identification of the rotary angle of ATP cleavage in F 1-ATPase from Bacillus PS3. Biophys J 2023; 122:554-564. [PMID: 36560882 PMCID: PMC9941720 DOI: 10.1016/j.bpj.2022.12.027] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Revised: 11/08/2022] [Accepted: 12/19/2022] [Indexed: 12/24/2022] Open
Abstract
F1-ATPase is the world's smallest biological rotary motor driven by ATP hydrolysis at three catalytic β subunits. The 120° rotational step of the central shaft γ consists of 80° substep driven by ATP binding and a subsequent 40° substep. In order to correlate timing of ATP cleavage at a specific catalytic site with a rotary angle, we designed a new F1-ATPase (F1) from thermophilic Bacillus PS3 carrying β(E190D/F414E/F420E) mutations, which cause extremely slow rates of both ATP cleavage and ATP binding. We produced an F1 molecule that consists of one mutant β and two wild-type βs (hybrid F1). As a result, the new hybrid F1 showed two pausing angles that are separated by 200°. They are attributable to two slowed reaction steps in the mutated β, thus providing the direct evidence that ATP cleavage occurs at 200° rather than 80° subsequent to ATP binding at 0°. This scenario resolves the long-standing unclarified issue in the chemomechanical coupling scheme and gives insights into the mechanism of driving unidirectional rotation.
Collapse
Affiliation(s)
- Yuh Hasimoto
- Tsukuba Research Center, Central Research Laboratory, Hamamatsu Photonics K.K., Ibaraki 300-2635, Japan.
| | - Mitsuhiro Sugawa
- Graduate School of Arts & Sciences, The University of Tokyo, Tokyo 153-8902, Japan
| | - Yoshihiro Nishiguchi
- Department of Physics, Faculty of Science, Gakushuin University, Tokyo 171-8588, Japan
| | - Fumihiro Aeba
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Ayari Tagawa
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Kenta Suga
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Nobukiyo Tanaka
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Hiroshi Ueno
- Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo, Tokyo, 113-8656, Japan
| | - Hiroki Yamashita
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Ryuichi Yokota
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan
| | - Tomoko Masaike
- Department of Applied Biological Science, Faculty of Science and Technology, Tokyo University of Science, Chiba 278-8510, Japan.
| | - Takayuki Nishizaka
- Department of Physics, Faculty of Science, Gakushuin University, Tokyo 171-8588, Japan.
| |
Collapse
|
2
|
Yadav S, Kunwar A. Temperature-Dependent Activity of Motor Proteins: Energetics and Their Implications for Collective Behavior. Front Cell Dev Biol 2021; 9:610899. [PMID: 33732692 PMCID: PMC7959718 DOI: 10.3389/fcell.2021.610899] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Accepted: 01/11/2021] [Indexed: 12/27/2022] Open
Abstract
Molecular motor proteins are an extremely important component of the cellular transport system that harness chemical energy derived from ATP hydrolysis to carry out directed mechanical motion inside the cells. Transport properties of these motors such as processivity, velocity, and their load dependence have been well established through single-molecule experiments. Temperature dependent biophysical properties of molecular motors are now being probed using single-molecule experiments. Additionally, the temperature dependent biochemical properties of motors (ATPase activity) are probed to understand the underlying mechanisms and their possible implications on the enzymatic activity of motor proteins. These experiments in turn have revealed their activation energies and how they compare with the thermal energy available from the surrounding medium. In this review, we summarize such temperature dependent biophysical and biochemical properties of linear and rotary motor proteins and their implications for collective function during intracellular transport and cellular movement, respectively.
Collapse
Affiliation(s)
- Saumya Yadav
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India
| | - Ambarish Kunwar
- Department of Biosciences and Bioengineering, Indian Institute of Technology Bombay, Mumbai, India
| |
Collapse
|
3
|
Essential Role of the ε Subunit for Reversible Chemo-Mechanical Coupling in F 1-ATPase. Biophys J 2019; 114:178-187. [PMID: 29320685 DOI: 10.1016/j.bpj.2017.11.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2017] [Revised: 10/31/2017] [Accepted: 11/06/2017] [Indexed: 11/22/2022] Open
Abstract
F1-ATPase is a rotary motor protein driven by ATP hydrolysis. Among molecular motors, F1 exhibits unique high reversibility in chemo-mechanical coupling, synthesizing ATP from ADP and inorganic phosphate upon forcible rotor reversal. The ε subunit enhances ATP synthesis coupling efficiency to > 70% upon rotation reversal. However, the detailed mechanism has remained elusive. In this study, we performed stall-and-release experiments to elucidate how the ε subunit modulates ATP association/dissociation and hydrolysis/synthesis process kinetics and thermodynamics, key reaction steps for efficient ATP synthesis. The ε subunit significantly accelerated the rates of ATP dissociation and synthesis by two- to fivefold, whereas those of ATP binding and hydrolysis were not enhanced. Numerical analysis based on the determined kinetic parameters quantitatively reproduced previous findings of two- to fivefold coupling efficiency improvement by the ε subunit at the condition exhibiting the maximum ATP synthesis activity, a physiological role of F1-ATPase. Furthermore, fundamentally similar results were obtained upon ε subunit C-terminal domain truncation, suggesting that the N-terminal domain is responsible for the rate enhancement.
Collapse
|
4
|
Elmore SE, La Merrill MA. Oxidative Phosphorylation Impairment by DDT and DDE. Front Endocrinol (Lausanne) 2019; 10:122. [PMID: 30915030 PMCID: PMC6422878 DOI: 10.3389/fendo.2019.00122] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/04/2018] [Accepted: 02/11/2019] [Indexed: 01/07/2023] Open
Abstract
There is increasing evidence supporting the characterization of the pesticide DDT and its metabolite, DDE, as obesogens and metabolic disruptors. Elucidating the mechanism is critical to understanding whether the association of DDT and DDE with obesity and diabetes is in fact causal. One area of research investigating the etiology of metabolic diseases is mitochondrial toxicity. Several studies have found associations between mitochondrial defects and insulin resistance, cellular respiration, substrate utilization, and energy expenditure. Although the mitotoxicity of DDT and DDE was established 20-40 years ago, it was not viewed in the light of the diseases faced today; therefore, it is prudent to reexamine the mitotoxicity literature for mechanistic support of DDT and DDE as causal contributors to obesity and diabetes, as well as associated diseases, such as cancer and Alzheimer's disease. This review aims to focus on studies investigating the effect of DDT or DDE on mammalian mitochondrial oxidative phosphorylation. We illustrate that both DDT and DDE impair the electron transport chain (ETC) and oxidative phosphorylation. We conclude that there is reasonable data to suggest that DDT and DDE target specific complexes and processes within the mitochondria, and that these insults could in turn contribute to the role of DDT and DDE in mitochondria-associated diseases.
Collapse
|
5
|
Tamiya Y, Watanabe R, Noji H, Li CB, Komatsuzaki T. Effects of non-equilibrium angle fluctuation on F 1-ATPase kinetics induced by temperature increase. Phys Chem Chem Phys 2018; 20:1872-1880. [PMID: 29292807 DOI: 10.1039/c7cp06256g] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
F1-ATPase (F1) is an efficient rotary protein motor, whose reactivity is modulated by the rotary angle to utilize thermal fluctuation. In order to elucidate how its kinetics are affected by the change in the fluctuation, we have extended the reaction-diffusion formalism [R. Watanabe et al., Biophys. J., 2013, 105, 2385] applicable to a wider range of temperatures based on experimental data analysis of F1 derived from thermophilic Bacillus under high ATP concentration conditions. Our simulation shows that the rotary angle distribution manifests a stronger non-equilibrium feature as the temperature increases, because ATP hydrolysis and Pi release are more accelerated compared with the timescale of rotary angle relaxation. This effect causes the rate coefficient obtained from dwell time fitting to deviate from the Arrhenius relation in Pi release, which has been assumed in the previous activation thermodynamic quantities estimation using linear Arrhenius fitting. Larger negative correlation is also found between hydrolysis and Pi release waiting time in a catalytic dwell with the increase in temperature. This loss of independence between the two successive reactions at the catalytic dwell sheds doubt on the conventional dwell time fitting to obtain rate coefficients with a double exponential function at temperatures higher than 65 °C, which is close to the physiological temperature of the thermophilic Bacillus.
Collapse
Affiliation(s)
- Yuji Tamiya
- Department of Mathematics, Hokkaido University, Sapporo 001-0020, Japan
| | | | | | | | | |
Collapse
|
6
|
Li J, He G, Hiroshi U, Liu W, Noji H, Qi C, Guo X. Direct Measurement of Single-Molecule Adenosine Triphosphatase Hydrolysis Dynamics. ACS NANO 2017; 11:12789-12795. [PMID: 29215860 DOI: 10.1021/acsnano.7b07639] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
F1-ATPase (F1) is a bidirectional molecular motor that hydrolyzes nearly all ATPs to fuel the cellular processes. Optical observation of labeled F1 rotation against the α3β3 hexamer ring revealed the sequential mechanical rotation steps corresponding to ATP binding/ADP release and ATP hydrolysis/Pi release. These substeps originate from the F1 rotation but with heavy load on the γ shaft due to fluorescent labeling and the photophysical limitation of an optical microscope, which hampers better understanding of the intrinsic kinetic behavior of ATP hydrolysis. In this work, we present a method capable of electrically monitoring ATP hydrolysis of a single label-free F1 in real time by using a high-gain silicon nanowire-based field-effect transistor circuit. We reproducibly observe the regular current signal fluctuations with two distinct levels, which are induced by the binding dwell and the catalytic dwell, respectively, in both concentration- and temperature-dependent experiments. In comparison with labeled F1, the hydrolysis rate of nonlabeled F1 used in this study is 1 order of magnitude faster (1.69 × 108 M-1 s-1 at 20 °C), and the differences between two sequential catalytic rates are clearer, demonstrating the ability of nanowire nanocircuits to directly probe the intrinsic dynamic processes of the biological activities with single-molecule/single-event sensitivity. This approach is complementary to traditional optical methods, offering endless opportunities to unravel molecular mechanisms of a variety of dynamic biosystems under realistic physiological conditions.
Collapse
Affiliation(s)
- Jie Li
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, P. R. China
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China
| | - Gen He
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, P. R. China
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China
| | - Ueno Hiroshi
- Department of Applied Chemistry, School of Engineering, The University of Tokyo , Tokyo 113-8654, Japan
| | - Wenzhe Liu
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China
| | - Hiroyuki Noji
- Department of Applied Chemistry, School of Engineering, The University of Tokyo , Tokyo 113-8654, Japan
| | - Chuanmin Qi
- Key Laboratory of Radiopharmaceuticals, Ministry of Education, College of Chemistry, Beijing Normal University , Beijing 100875, P. R. China
| | - Xuefeng Guo
- Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University , Beijing 100871, P. R. China
- Department of Materials Science and Engineering, College of Engineering, Peking University , Beijing 100871, P. R. China
| |
Collapse
|
7
|
Chapman B, Loiselle D. Thermodynamics and kinetics of the FoF1-ATPase: application of the probability isotherm. ROYAL SOCIETY OPEN SCIENCE 2016; 3:150379. [PMID: 26998316 PMCID: PMC4785967 DOI: 10.1098/rsos.150379] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 01/08/2016] [Indexed: 06/05/2023]
Abstract
We use the results of recent publications as vehicles with which to discuss the thermodynamics of the proton-driven mitochondrial F o F1-ATP synthase, focusing particularly on the possibility that there may be dissociation between rotatory steps and ATP synthesis/hydrolysis. Such stoichiometric 'slippage' has been invoked in the literature to explain observed non-ideal behaviour. Numerical solution of the Rate Isotherm (the kinetic equivalent of the more fundamental Probability Isotherm) suggests that such 'slippage' is an unlikely explanation; instead, we suggest that the experimental results may be more consistent with damage to the enzyme caused by its isolation from the biomembrane and its experimental fixation, resulting in non-physiological friction within the enzyme's rotary mechanism. We emphasize the unavoidable constraint of the Second Law as instantiated by the obligatory dissipation of Gibbs Free Energy if the synthase is to operate at anything other than thermodynamic equilibrium. We use further numerical solution of the Rate Isotherm to demonstrate that there is no necessary association of low thermodynamic efficiency with high metabolic rates in a bio-world in which the dominating mechanism of metabolic control is multifactorial enzyme activation.
Collapse
Affiliation(s)
- Brian Chapman
- Honorary Principal Research Fellow, School of Applied and Biomedical Science, Faculty of Science and Technology, Federation University Australia, Victoria, Australia
| | - Denis Loiselle
- Department of Physiology and the Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand
| |
Collapse
|
8
|
Watanabe R, Koyasu K, You H, Tanigawara M, Noji H. Torque transmission mechanism via DELSEED loop of F1-ATPase. Biophys J 2016; 108:1144-52. [PMID: 25762326 DOI: 10.1016/j.bpj.2015.01.017] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 01/16/2015] [Accepted: 01/21/2015] [Indexed: 12/01/2022] Open
Abstract
F1-ATPase (F1) is an ATP-driven rotary motor in which the three catalytic β subunits in the stator ring sequentially induce the unidirectional rotation of the rotary γ subunit. Many lines of evidence have revealed open-to-closed conformational transitions in the β subunit that swing the C-terminal domain inward. This conformational transition causes a C-terminal protruding loop with conserved sequence DELSEED to push the γ subunit. Previous work, where all residues of DELSEED were substituted with glycine to disrupt the specific interaction with γ and introduce conformational flexibility, showed that F1 still rotated, but that the torque was halved, indicating a remarkable impact on torque transmission. In this study, we conducted a stall-and-release experiment on F1 with a glycine-substituted DELSEED loop to investigate the impact of the glycine substitution on torque transmission upon ATP binding and ATP hydrolysis. The mutant F1 showed a significantly reduced angle-dependent change in ATP affinity, whereas there was no change in the equilibrium for ATP hydrolysis. These findings indicate that the DELSEED loop is predominantly responsible for torque transmission upon ATP binding but not for that upon ATP hydrolysis.
Collapse
Affiliation(s)
- Rikiya Watanabe
- Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, Tokyo, Japan; PRESTO, Japan Science and Technology Agency, Tokyo, Japan; CREST, Japan Science and Technology Agency, Tokyo, Japan
| | - Kazuma Koyasu
- Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, Tokyo, Japan
| | - Huijuan You
- Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, Tokyo, Japan
| | - Mizue Tanigawara
- Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, Tokyo, Japan
| | - Hiroyuki Noji
- Department of Applied Chemistry, Graduate School of Engineering, University of Tokyo, Tokyo, Japan; CREST, Japan Science and Technology Agency, Tokyo, Japan.
| |
Collapse
|
9
|
Abstract
Technical progress in laser-sources and detectors has allowed the temporal and spatial resolution of chemical reactions down to femtoseconds and Å-units. In photon-excitable systems the key to chemical kinetics, trajectories across the vibrational saddle landscape, are experimentally accessible. Simple and thus well-defined chemical compounds are preferred objects for calibrating new methodologies and carving out paradigms of chemical dynamics, as shown in several contributions to this Faraday Discussion. Aerobic life on earth is powered by solar energy, which is captured by microorganisms and plants. Oxygenic photosynthesis relies on a three billion year old molecular machinery which is as well defined as simpler chemical constructs. It has been analysed to a very high precision. The transfer of excitation between pigments in antennae proteins, of electrons between redox-cofactors in reaction centres, and the oxidation of water by a Mn4Ca-cluster are solid state reactions. ATP, the general energy currency of the cell, is synthesized by a most agile, rotary molecular machine. While the efficiency of photosynthesis competes well with photovoltaics at the time scale of nanoseconds, it is lower by an order of magnitude for crops and again lower for bio-fuels. The enormous energy demand of mankind calls for engineered (bio-mimetic or bio-inspired) solar-electric and solar-fuel devices.
Collapse
Affiliation(s)
- Wolfgang Junge
- Dept. Biology & Chemistry, University of Osnabrück, R. 35/E42 Barbarastrasse 11, 49076 Osnabrück, Germany.
| |
Collapse
|
10
|
Abstract
Oxygenic photosynthesis is the principal converter of sunlight into chemical energy. Cyanobacteria and plants provide aerobic life with oxygen, food, fuel, fibers, and platform chemicals. Four multisubunit membrane proteins are involved: photosystem I (PSI), photosystem II (PSII), cytochrome b6f (cyt b6f), and ATP synthase (FOF1). ATP synthase is likewise a key enzyme of cell respiration. Over three billion years, the basic machinery of oxygenic photosynthesis and respiration has been perfected to minimize wasteful reactions. The proton-driven ATP synthase is embedded in a proton tight-coupling membrane. It is composed of two rotary motors/generators, FO and F1, which do not slip against each other. The proton-driven FO and the ATP-synthesizing F1 are coupled via elastic torque transmission. Elastic transmission decouples the two motors in kinetic detail but keeps them perfectly coupled in thermodynamic equilibrium and (time-averaged) under steady turnover. Elastic transmission enables operation with different gear ratios in different organisms.
Collapse
Affiliation(s)
- Wolfgang Junge
- Department of Biophysics, Universität Osnabrück, DE-49069 Osnabrück, Germany;
| | | |
Collapse
|
11
|
Enoki S, Iino R, Niitani Y, Minagawa Y, Tomishige M, Noji H. High-speed angle-resolved imaging of a single gold nanorod with microsecond temporal resolution and one-degree angle precision. Anal Chem 2015; 87:2079-86. [PMID: 25647635 DOI: 10.1021/ac502408c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
We developed two types of high-speed angle-resolved imaging methods for single gold nanorods (SAuNRs) using objective-type vertical illumination dark-field microscopy and a high-speed CMOS camera to achieve microsecond temporal and one-degree angle resolution. These methods are based on: (i) an intensity analysis of focused images of SAuNR split into two orthogonally polarized components and (ii) the analysis of defocused SAuNR images. We determined the angle precision (statistical error) and accuracy (systematic error) of the resultant SAuNR (80 nm × 40 nm) images projected onto a substrate surface (azimuthal angle) in both methods. Although both methods showed a similar precision of ∼1° for the azimuthal angle at a 10 μs temporal resolution, the defocused image analysis showed a superior angle accuracy of ∼5°. In addition, the polar angle was also determined from the defocused SAuNR images with a precision of ∼1°, by fitting with simulated images. By taking advantage of the defocused image method's full revolution measurement range in the azimuthal angle, the rotation of the rotary molecular motor, F1-ATPase, was measured with 3.3 μs temporal resolution. The time constants of the pauses waiting for the elementary steps of the ATP hydrolysis reaction and the torque generated in the mechanical steps have been successfully estimated. The high-speed angle-resolved SAuNR imaging methods will be applicable to the monitoring of the fast conformational changes of many biological molecular machines.
Collapse
Affiliation(s)
- Sawako Enoki
- Department of Applied Chemistry, Graduate School of Engineering, The University of Tokyo , Tokyo 113-8656, Japan
| | | | | | | | | | | |
Collapse
|
12
|
Watanabe R, Minagawa Y, Noji H. Thermodynamic analysis of F1-ATPase rotary catalysis using high-speed imaging. Protein Sci 2014; 23:1773-9. [PMID: 25262814 DOI: 10.1002/pro.2559] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2014] [Accepted: 09/23/2014] [Indexed: 11/05/2022]
Abstract
F1-ATPase (F1) is a rotary motor protein fueled by ATP hydrolysis. Although the mechanism for coupling rotation and catalysis has been well studied, the molecular details of individual reaction steps remain elusive. In this study, we performed high-speed imaging of F1 rotation at various temperatures using the total internal reflection dark-field (TIRDF) illumination system, which allows resolution of the F1 catalytic reaction into elementary reaction steps with a high temporal resolution of 72 µs. At a high concentration of ATP, F1 rotation comprised distinct 80° and 40° substeps. The 80° substep, which exhibited significant temperature dependence, is triggered by the temperature-sensitive reaction, whereas the 40° substep is triggered by ATP hydrolysis and the release of inorganic phosphate (Pi). Then, we conducted Arrhenius analysis of the reaction rates to obtain the thermodynamic parameters for individual reaction steps, that is, ATP binding, ATP hydrolysis, Pi release, and TS reaction. Although all reaction steps exhibited similar activation free energy values, ΔG(‡) = 53-56 kJ mol(-1), the contributions of the enthalpy (ΔH(‡)), and entropy (ΔS(‡)) terms were significantly different; the reaction steps that induce tight subunit packing, for example, ATP binding and TS reaction, showed high positive values of both ΔH(‡) and ΔS(‡). The results may reflect modulation of the excluded volume as a function of subunit packing tightness at individual reaction steps, leading to a gain or loss in water entropy.
Collapse
Affiliation(s)
- Rikiya Watanabe
- Department of Applied Chemistry, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo, 113-8656, Japan; PRESTO, JST, Bunkyo-ku, Tokyo, 113-8656, Japan
| | | | | |
Collapse
|