Chemomechanical Energy Conversion Research Articles

Structural criticality manifested by a polarized ionic layer on a MWCNT yarn surface under mechanical loading

The electrochemical capacitance of an energy harvester based on a multiwalled carbon-nanotube yarn is proportional to the total strain and then rapidly decreases after the strain exceeds a critical value. Rigorous characterization of the nonlinearities in the distortion of the polarized ion layer under an external load is necessary to systematically optimize the performance of energy-harvesting fibers. In this study, we conducted electrochemical experiments and all-atom molecular dynamics simulations to elucidate the dynamics of an ionic polarization layer on a nanotube surface. The in-plane compressive strain exerted under the mechanical tension of the energy harvester induced the radial buckling of the nanotubes, which in turn became the driving force behind the repulsion between adjacent polar ion layers. Therefore, electrochemical stability was guaranteed only under structural stability and the resulting elastic deformation experienced by each nanotube. The proposed mechanism reveals the available mechanical range wherein the polarized ionic layers can substantially function in chemomechanical energy conversion.

Mechanism of Ultra-Fast Actin-Myosin Sliding Producing Cytoplasmic Streaming in Giant Algal Cell, Studied Using the Centrifuge Microscope

In giant intermodal cells of green algae Chara collaria, cytoplasmic streaming is produced by ATP-dependent sliding between myosin heads extending from amorphous cytoplasmic organelles and actin filament arrays (actin cables) fixed on chloroplast rows. The velocity of cytoplasmic streaming is many times faster than the maximum myofilament sliding in skeletal muscle. In this article, we compared steady-state force-velocity (P-V) relations between cytoplasmic myosin and skeletal and cardiac muscle myosins using the centrifuge microscope, in which myosincoated latex beads were made to slide along the actin cables under various centrifugal forces. In contrast with the hyperbolic P-V relation of actin-myosin sliding in skeletal and cardiac myosins, the P-V relation of cytoplasmic myosin versus actin cable sliding was a straight line, indicating a very large duty ratio and a very small rate of chemomechanical energy conversion. Possible mechanisms of the ultra-fast actin-myosin sliding are discussed.Highlights• The velocity of cytoplasmic streaming, caused by ATP-dependent sliding between cytoplasmic myosin and actin cables in giant algal cells is many times faster than ATP-dependent actin-myosin sliding in skeletal and cardiac muscles.• The mechanism of ultra-fast actin-myosin sliding was studied using the centrifuge microscope, in which beads coated with cytoplasmic myosin were made to slide along actin cables under various centrifugal forces serving as loads against cytoplasmic myosin versus actin cable sliding.• Unlike the hyperbolic force-velocity (P-V) relation of skeletal and cardiac muscle actin-myosin sliding, the P-V relation of cytoplasmic actin myosin sliding was a straight line irrespective of the force generated by cytoplasmic myosin.• These results indicate a very large duty ratio and a very small efficiency of chemo-mechanical energy conversion in cytoplasmic actin-myosin sliding.

Design of Self-Oscillating Polymer Brushes and Control of the Dynamic Behaviors

A polymer brush surface with autonomous function has been designed by using a self-oscillating polymer that we developed. The self-oscillation is induced by chemomechanical energy conversion from an oscillating chemical reaction (the Belousov–Zhabotinsky (BZ) reaction) to conformational changes of polymer chains. In this study, the surface nanostructure of polymer brushes were regulated and the spatiotemporal behaviors of self-oscillation were investigated. The target polymer brush surfaces were prepared through surface-initiated atom transfer radical polymerization (SI-ATRP) of N-isopropylacrylamide (NIPAAm) and N-(3-aminopropyl) methacrylamide (NAPMAm), and the subsequent conjugation of Ru(bpy)3 to the amino group of NAPMAm. The characterization of the prepared polymer brush and the free polymer was determined by X-ray photoelectron spectroscopy, atomic force microscopy, attenuated total reflection Fourier transform infrared spectroscopy, UV–vis spectrophotometry, gel permeation chromatography, and 1H N...

Simple mechanism whereby the F1-ATPase motor rotates with near-perfect chemomechanical energy conversion

F1-ATPase is a motor enzyme in which a central shaft γ subunit rotates 120° per ATP in the cylinder made of α3β3 subunits. During rotation, the chemical energy of ATP hydrolysis (ΔGATP) is converted almost entirely into mechanical work by an elusive mechanism. We measured the force for rotation (torque) under various ΔGATP conditions as a function of rotation angles of the γ subunit with quasi-static, single-molecule manipulation and estimated mechanical work (torque × traveled angle) from the area of the function. The torque functions show three sawtooth-like repeats of a steep jump and linear descent in one catalytic turnover, indicating a simple physical model in which the motor is driven by three springs aligned along a 120° rotation angle. Although the second spring is unaffected by ΔGATP, activation of the first spring (timing of the torque jump) delays at low [ATP] (or high [ADP]) and activation of the third spring delays at high [Pi]. These shifts decrease the size and area of the sawtooth (magnitude of the work). Thus, F1-ATPase responds to the change of ΔGATP by shifting the torque jump timing and uses ΔGATP for the mechanical work with near-perfect efficiency.

Key chemical factors of arginine finger catalysis of F1-ATPase clarified by an unnatural amino acid mutation.

A catalytically important arginine, called Arg finger, is employed in many enzymes to regulate their functions through enzymatic hydrolysis of nucleotide triphosphates. F1-ATPase (F1), a rotary motor protein, possesses Arg fingers which catalyze hydrolysis of adenosine triphosphate (ATP) for efficient chemomechanical energy conversion. In this study, we examined the Arg finger catalysis by single-molecule measurements for a mutant of F1 in which the Arg finger is substituted with an unnatural amino acid of a lysine analogue, 2,7-diaminoheptanoic acid (Lyk). The use of Lyk, of which the side chain is elongated by one CH2 unit so that its chain length to the terminal nitrogen of amine is set to be equal to that of arginine, allowed us to resolve key chemical factors in the Arg finger catalysis, i.e., chain length matching and chemical properties of the terminal groups. Rate measurements by single-molecule observations showed that the chain length matching of the side-chain length is not a sole requirement for the Arg finger to catalyze the ATP hydrolysis reaction step, indicating the crucial importance of chemical properties of the terminal guanidinium group in the Arg finger catalysis. On the other hand, the Lyk mutation prevented severe formation of an ADP inhibited state observed for a lysine mutant and even improved the avoidance of inhibition compared with the wild-type F1. The present study demonstrated that incorporation of unnatural amino acids can widely extend with its high "chemical" resolution biochemical approaches for elucidation of the molecular mechanism of protein functions and furnishing novel characteristics.

REMOVED: Chemo–mechanical Energy Conversion Device with Enzyme Diaphragm Membrane for Kinetic Biosensors and Drug Release System

REMOVED: Chemo–mechanical Energy Conversion Device with Enzyme Diaphragm Membrane for Kinetic Biosensors and Drug Release System

J112011 血糖成分グルコースをエネルギーとして駆動するアクチュエータ(有機エンジン)([J11201]次世代アクチュエータシステム(1))

High power decompression unit of an autonomous drug release system based on chemo-mechanical energy conversion was developed. The decompression unit was fabricated by separating a cylindrical cell into a top cell (gas phase) and a bottom cell (liquid phase) by glucoseoxidase (GOD) enzyme immobilized membrane. The enzyme membrane recognizes glucose and converts chemical energy found in glucose to mechanical energy. In this study, the decompression unit increased membrane area per cell volume (0.73 ・ 3.00 cm2/m1) was fabricated in order to drive by lower glucose concentration. As a result, the improved cell connected to pressure release valve was successfully driven by 25 mM glucose solution (a conventional cell was driven by 100 mM). The possibility of autonomous drug release systems to control the patient's own blood sugar levels was suggested.

An autonomous drug release system based on chemo-mechanical energy conversion “Organic Engine” for feedback control of blood glucose

A novel autonomous drug release system was fabricated and tested. The system consists of two integrated units: decompression unit and drug release unit. The decompression unit was fabricated by separating a cylindrical cell into a top cell (gas phase) and a bottom cell (liquid phase) by glucose oxidase (GOD) enzyme immobilized membrane. The enzyme membrane recognizes glucose and converts chemical energy found in glucose to mechanical energy. The linear correlation between glucose concentration and de-pressure slope of the top cell was revealed as applying glucose solution to the bottom cell. Afterward, the drug release unit which utilizes the energy of the decompression unit as a power source was fabricated and evaluated by recording its release actions. The drug release unit was made to release at a constant quantity of drug in the liquid phase. The system was then fabricated by combining the decompression unit and the drug release unit. And it was evaluated in an open loop and in a closed loop by applying a mixture of glucose solution (100 mmol/l) and NADH + using glucose dehydrogenase enzyme (GDH) as a glucose reducer. Glucose concentration decreased gradually in the closed loop and, as a consequence, interval time of the GDH release became longer. In other words, an inverse correlation between actuation interval of the system and glucose concentration was shown. As a result, the possibility of feedback control of glucose concentration by the drug release system without external energy was confirmed.

化学‐力学エネルギー変換（有機エンジン）を用いた自律駆動型薬物放出システム

A novel drug-injection system that utilities direct chemo-mechanical energy conversion was fabricated and demonstrated for feedback control of glucose level. The system consists of two integrated units, decompression unit and drug release unit. The decompression unit was fabricated by separating a cylindrical cell into a top cell (gas phase) and a bottom cell (liquid phase) by glucose oxidase (GOD) enzyme immobilized membrane. The enzyme membrane recognizes glucose and converts chemical energy into pressure decreaese by consuming oxgen. The linear correlation between glucose concentration and de-pressure slope of the top cell was revealed as applying glucose solution to the bottom cell. The drug release unit which utilizes the energy of the decompression unit as a power source was evaluated by recording its release actions. The system is expected to be used in intelligent actuators without external energy.

Three-dimensional structures of the flagellar dynein–microtubule complex by cryoelectron microscopy

The outer dynein arms (ODAs) of the flagellar axoneme generate forces needed for flagellar beating. Elucidation of the mechanisms underlying the chemomechanical energy conversion by the dynein arms and their orchestrated movement in cilia/flagella is of great importance, but the nucleotide-dependent three-dimensional (3D) movement of dynein has not yet been observed. In this study, we establish a new method for reconstructing the 3D structure of the in vitro reconstituted ODA–microtubule complex and visualize nucleotide-dependent conformational changes using cryoelectron microscopy and image analysis. As the complex went from the rigor state to the relaxed state, the head domain of the β heavy chain shifted by 3.7 nm toward the B tubule and inclined 44° inwards. These observations suggest that there is a mechanism that converts head movement into the axonemal sliding motion.

Biomimetic model of skeletal muscle isometric contraction: I. an energetic–viscoelastic model for the skeletal muscle isometric force twitch

This paper describes a revision of the Hill-type muscle model so that it will describe the chemo-mechanical energy conversion process (energetic) and the internal-element stiffness variation (viscoelastic) during a skeletal muscle isometric force twitch contraction. The derivation of this energetic–viscoelastic model is described by a first-order linear ordinary differential equation with constant energetic and viscoelastic coefficients. The model has been implemented as part of a biomimetic model, which describes the excitation–contraction coupling necessary to drive the energetic–viscoelastic model. Finally, the energetic–viscoelastic model is validated by comparing its isometric force–time profile with that of various muscles reported in the literature.

The 55th Annual Meeting and Symposium of the Society of General Physiologists: molecular motors.

(Organized by H. Lee Sweeney, Erika L.F. Holzbaur, and E. Michael Ostap) Muscle contraction and cell motility arise from the conversion of chemical energy, in the form of ATP hydrolysis, into mechanical work. The conceptual scheme for this chemomechanical energy conversion is the Lymn-Taylor four-

Evidence for the load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP.

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, after laser-flash photolysis of caged calcium. Immediately before laser-flash activation, almost all of the myosin heads in the fiber are in the state M.ADP.Pi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force, and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of M.ADP.Pi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemomechanical energy conversion in individual myosin heads changes in a load-dependent manner.

Load-dependent mechanical efficiency of individual myosin heads in skeletal muscle fibers activated by laser flash photolysis of caged calcium in the presence of a limited amount of ATP.

Although a contracting muscle regulates its energy output depending on the load imposed on it ("Fenn effect"), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, following laser flash photolysis of caged calcium. Immediately before laser flash activation, almost all of the myosin heads in the fiber are in the state, M.ADP.Pi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of M.ADP.Pi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition, and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemo-mechanical energy conversion in individual myosin heads changes in a load-dependent manner.

On the Thermodynamics of Chemomechanical Energy Conversion Realised by Neutral Gels

Chemomechamcal energy conversion exhibited by a gel lever has been studied both theoretically and experimentally. Based on the thermodynamical theory of anisotropic swelling, the effective mechanical work produced, the chemical energy consumed, and the efficiency of conver sion are discussed. The results of model calculations are compared with real experiments performed on water-swollen poly(vinyl alcohol) gels. The mechanical work as well as the free energy change during the process have been determined from experimental data.

Molecular mechanism of ATP-dependent actin-myosin interaction in muscle contraction.

Among a variety of energy transduction mechanisms in biological systems, the mechanism of chemo-mechanical energy conversion in muscle contraction has been studied most intensively. From the standpoint of muscle biochemistry, muscle contraction is essentially the actomyosin ATPase reaction in solution. From the standpoint of muscle physiology, on the other hand, muscle contraction is the relative sliding between the thick and thin filaments resulting from the attachment-detachment cycle between actin and myosin. Although the large gap between muscle physiology and muscle biochemistry is now being gradually eliminated by various new experimental techniques such as the flash photolysis of caged compounds and in vitro motility assay systems, there still remain a number of uncertainties concerning the molecular mechanism of actin-myosin interaction coupled with hydrolysis of ATP. As described in this article, attention of most investigators in this research field has been focused on the detection of myosin head rotation coupled with muscle force generation. Unfortunately, however, attempts to detect the myosin head rotation have not yet been successful, despite the efforts of many investigators with various techniques including X-ray diffraction, quick freezing, and use of various probes attached to the myosin head. It seems therefore possible that the mechanism of muscle contraction might be different from the mechanism which have been generally accepted. This possibility seems to be supported, for example, by the unexpected dissociation between the ATPase activity and the force development in muscle fibers treated with anti-S-2 antibody (Fig. 9C).

Swelling properties of partially hydrolyzed polyacrylamide gels and gelatin gels in aqueous media

Volume changes of polymer networks composed of ionizable functions depend on the nature of the solvent, the pH and the ionic strength. We have studied the dependence of volume changes (swelling ratio) of partially hydrolyzed polyacrylamide (PHPA) gels as a function of pH and ionic strength. The swelling force (the force exerted by the polymer network when it is confined in a cell of constant volume) of a gel composed of ionizable functions depends on pH and ionic strength. The variation of gel volume or swelling force involves a chemo-mechanical energy conversion. This aspect is briefly discussed. In addition, the variation of swelling properties of these polyelectrolytic gels has been compared with the variation of rheological properties of a solution of the same polyelectrolyte.

A Monte Carlo study of stochastic phenomena in biological systems—: I. Mathematical treatment of the geometrical structure of muscle

The geometrical structure of the molecular constitution of muscle is studied mathematically with regard to the elementary processes of chemomechanical energy conversion caused by the interaction between cross-bridges and actin sites. Based on a simplified model for the half-sarcomere, the structural unit of muscle, examinations are made by computer simulation of the effect of geometrical structure on muscle contraction and of its influence on the stochastic behavior of the elementary process. It is shown that muscle contraction sharply depends on the geometrical structure even if the property of individual elementary process is the same, and that a cyclic change, called a “reverberation,” appears among elementary processes only when the geometrical structure satisfies some mathematical conditions, as the natural structure in fact does. It is also shown that the noise in the elementary process is much reduced when the elementary processes are connected by a reverberation cycle, which leads to smooth and efficient contraction of muscle.