Staggered movement of an actin filament sliding on myosin molecules in the presence of ATP

Quantitative assessments of adenosine triphosphatase hydrolytic activity by ultrafiltration-coupled ion-pair reversed-phase high-performance liquid chromatography

Adenosine triphosphate is a universal energy currency that can directly provide energy required for a multitude of biochemical reactions and biophysical actions through adenosine triphosphatase catalyzed hydrolysis. Adenosine triphosphatase activity is thus one important feature for the characterization of protein function and cell activity. Herein, we optimized ion-pair reversed-phase high-performance liquid chromatography technique for highly efficient separation of adenosine triphosphate, adenosine diphosphate, and adenosine monophosphate, and the method demonstrated good linearity. Moreover, by coupling a protein-removable ultrafiltration, we developed a sensitive and robust approach for quantification of adenosine triphosphatase hydrolytic activity. By this assay, we demonstrated that RecA filaments-catalyzed adenosine triphosphate hydrolysis approached a second-order reaction, and its rate constant was estimated as 0.057 mM^-1  min^-1 . In addition, we explored the effects of DNA length on this reaction and revealed that the increase of the length of single-stranded DNA can promote the adenosine triphosphatase hydrolytic activity of RecA filaments. All these results confirm the feasibility of this new method in quantification of adenosine triphosphatase hydrolytic activity assays. Compared with previous complicated enzyme-coupled or homogeneous colorimetric measurements, the developed approach with high resolution separation allows a simple reaction system for adenosine triphosphatase assay and a sensitive detection free of interference from background noise.

Longitudinal distortions and transversal fluctuations of an actin filament sliding on Myosin molecules

An actin filament sliding on myosin moleculesdemonstrates both longitudinal distortions and transversal fluctuationswith the linear dimension far exceeding the diameter of an actinmonomer. Local swaying of a single actin filament was identified byreading speckled fluorescent markers attached on the filament. Theaccuracy of reading each speckled marker was about 10.4 nm (r.m.s.).Longitudinal distortions of an actin filament at a low ATP concentrationof 20 μM were as much as 0.5 μm for the average filament lengthof 5.4 μm. The magnitude of transversal fluctuations was as much as60 nm, that was independent of the filament length. Both longitudinaldistortions and transversal fluctuations are suggested to play a pivotalrole for facilitating a smooth sliding movement of an actin filament.

Slowly modulating fluctuations as mesoscopic distortions occurring on an actin filament

An actin filament sliding on myosin molecules exhibits fluctuating or staggered movements as responding to changes in the ATP concentration. We previously observed that fluctuations in the sliding velocity enhanced in a manner being independent of the magnitude of the velocity. The present study focused upon a single actin filament bound to a glass surface through avidin-biotin bonding to examine those fluctuations inherent to the filament in the presence of heavy meromyosin. The auto-correlation analysis revealed that the relaxation time of fluctuations in the filamental displacement obtains its maximum value at about 100microM of the ATP concentration in the ambient, while the magnitude of the fluctuations gradually increased with an increase of the concentration. Furthermore, the measurement of the fluorescence intensity from the markers fixed on the filament demonstrated an enhancement of the negative correlation between the measured peak intensity and the spatial spreading of its intensity over the range of 0-200microM of the ATP concentration, as indicating both development and mitigation of local distortions occurring within the filament.

Relationship between the flexibility and the motility of actin filaments: effects of pH

Both the sliding velocity of fluorescently labeled actin filament and its persistence length as an index of the bending flexibility of the filament were examined in the motility assay as varying the pH values of the solution for preparing actin filaments. When the pH value was varied from 5.0 to 9.0 in the solution in which actin filaments were formed from the constituent monomers, the motile performance of Mg(2+) bound actin filaments (Mg-F-actin) was apparently suppressed compared to the case of Ca(2+) bound ones (Ca-F-actin). The persistence length for Ca-F-actin gradually increased with the increase of the pH value while the similar length for Mg-F-actin remained rather independent of the value. The largest sliding velocity of the filament, on the other hand, obtained at the persistence length of roughly 6 microm for both cases of Mg-F-actin and Ca-F-actin.

Unidirectional movement of an actin filament taking advantage of temperature gradients

An actin filament with heat acceptors attached to its Cys374 residue in each actin monomer could move unidirectionally even under heat pulsation alone, while in the total absence of both ATP and myosin. The prime driver for the movement was temperature gradients operating between locally heated portions on an actin filament and its cooler surroundings. In this report, we investigated how the mitigation of the temperature gradients induces a unidirectional movement of an actin filament. We then observed the transversal fluctuations of the filament in response to heat pulsation and their transition into longitudinally unidirectional movement. The transition was significantly accelerated when Cys374 and Lys336 were simultaneously excited within an actin monomer. These results suggest that the mitigation of the temperature gradients within each actin monomer first went through the energy transformation to transversal fluctuations of the filament, and then followed by the transformation further down to longitudinal movements of the filament. The faster mitigation of temperature gradients within actin monomer helps build up the transition from the transversal to longitudinal movements of the filament by coordinating the interaction between the neighboring monomers.

Enhancing the staggered fluctuations of an actin filament sliding on Chara myosin

We examined both longitudinal and transversal fluctuations of displacements of an actin filament sliding upon Chara myosin molecules. Although the magnitude of transversal fluctuations remained rather independent of ATP concentration, the longitudinal ones were found to increase their magnitude as the concentration increased. In addition, the longitudinal fluctuations gradually increased as the sliding velocity of the filament increased.

Transition from contractile to protractile distortions occurring along an actin filament sliding on myosin molecules

An ATP-activated actin filament sliding on myosin molecules exhibited mechanical distortions or fluctuations both longitudinally and transversally along the filament. Although actin filaments exhibited a uniform sliding movement longitudinally as the ATP concentration increased, the longitudinal fluctuations were found to vary their magnitude with the concentration. The magnitude of longitudinal fluctuations reached its maximum at approximately 100 microM of the ATP concentration. The local enhancement of the longitudinal fluctuations as responding to changes in the ATP concentration is associated with a critical phenomenon bridging the two different kinds of mechanical distortions, either contractile or protractile ones, occurring within a sliding actin filament.

Enhancement of the sliding velocity of actin filaments in the presence of ATP analogue: AMP-PNP

The sliding velocity of actin filaments was found to increase in the presence of ATP analogues. At 0.5 mM ATP, the presence of 2.0 mM of AMP-PNP enhanced the filament velocity from 3.2 up to 4.5 microm/s. However, 2 mM ADP decreased the velocity down to 1.1 microm/s. The results suggest that the complex conformations of myosin cross-bridges interacting with an actin filament in the presence of ATP analogues makes the entire filament move faster.

Quantum mechanics in first, second and third person descriptions

Although quantum mechanics in third person descriptions is certainly legitimate insofar as one is sure about what each energy quantum is all about, quantum mechanics in first person descriptions comes to the surface once one raises the issue of how each quantum transforms itself as measuring and interacting with the others of the similar nature. Each energy quantum is taken as the robust confinement of interactions, whose first person descriptions address the quantum involved in the process of measuring other quanta internally. In addition, the issue of how the robust confinement of interactions could come into being and develop is a matter of quantum mechanics in second person descriptions. Biological activities including cell motility and muscle contraction address the issue of quantum coherence accessible in quantum mechanics in second person descriptions.

Cell motility and thermodynamic fluctuations tailoring quantum mechanics for biology

Cell motility underlying muscle contraction is an instance of thermodynamics tailoring quantum mechanics for biology. Thermodynamics is intrinsically multi-agential in admitting energy consumers in the form of energy-deficient thermodynamic fluctuations. The onset of sliding movement of an actin filament on myosin molecules in the presence of ATP molecules to be hydrolyzed demonstrates that thermodynamic fluctuations transform their nature so as to accommodate themselves to energy transduction subject to the first law of thermodynamics. The transition from transversal to longitudinal fluctuations of an actin filament with the increase of ATP concentration coincides with the change in the nature of energy consumers acting upon thermal energy in the light of the first law, eventually embodying a uniform sliding movement of an actin filament.

The internalist enterprise on constructing cell motility in a bottom-up manner

Quantum coherence in the biological realm is constructed internally in a bottom-up manner. In particular, an actin filament sliding on myosin molecules in the presence of ATP to be hydrolyzed as a functional unit of muscle contraction exhibits magnetization as a marker of quantum coherence. The uniqueness of quantum coherence in biology is found in precipitating synchronous time in interaction from the interacting energy quanta, each of which has carried with itself synchronous time unique to the quantum in isolation. It exhibits a marked contrast to quantum coherence met in low temperature physics, in the latter of which no transformation of the nature of synchronous time is entertained.

The internalist stance. A linguistic practice enclosing dynamics

Natural dynamics, as manifested in evolutionary processes, refer to material bodies in movement in the present progressive mode. Any interacting material body in the present progressive mode must be sentient to others because there can be no global agency coordinating it to others in a globally synchronous manner. The internalist perspective, or the worm's eye view, referring primarily to the present progressive mode, renders local material bodies, large or small, subject to an inevitable inconsistency among local representations of neighborhood events registered in the local present perfect tense. Any sentient material body experiencing this inconsistency subsequently transforms itself into an inconsistency-free representation. The descriptive scheme unique to the internalist stance is internal and dynamic in the sense that it constantly strives to update constituent local representations, attempting to eliminate any inconsistencies residing within antecedent local representations. Compared to external descriptions of invariable universals grounded upon the Cartesian epistemic split, which are complementary to dynamics, internal description serves as a linguistic means of embodying natural dynamics even without recourse to the notion called forces. This makes our language powerful enough to enclose natural dynamics of material bodies in the empirical domain.

Onset of the sliding movement of an actin filament on myosin molecules: from isotropic to anisotropic fluctuations

An actin filament contacting myosin molecules increased the fluctuation intensity of the filamental displacement as the ATP concentration increased. In particular, fluctuations in the filamental displacement in the planar plane in which the sliding movement takes place were isotropic at a low ATP concentration, and became anisotropic as the concentration increased. The build-up of the sliding movement of an actin filament was associated with the transformation from isotropic to anisotropic fluctuations of the filamental displacement.

Contractile and protractile coordination within an actin filament sliding on myosin molecules

An actin filament exhibits distortions longitudinally when it slides upon myosin molecules. We observed that the actin filament demonstrated contractile distortions at low ATP concentrations and protractile distortions at high concentrations. Temporal development of such distortions was identified, by tracing each of several speckled fluorescent markers attached to the actin filament. Close association of the sliding movement to the moving distortions of an actin filament suggests the presence of a unitary mechanism regulating the apparently two different modes of dynamic movement.

Cell motility as an entangled quantum coherence

Cell motility underlying muscle contraction is imputed to a macroscopic quantum mechanical coherence actualized locally in the body of a biological organism. Actin-activated myosin ATPase activity functions as a heat sink operating effectively at an extremely low temperature. Extraction of heat energy from the actin filament can help condensing the atomic degrees of freedom constituting the filament into a macroscopic quantum state carrying a nonvanishing linear momentum. Sliding movement of an actin filament on myosin molecules while hydrolyzing ATP molecules is a consequence of the quantum mechanical coherence due to an extremely slow release of energy stored in an ATP molecule.

Quantum mechanics in the present progressive mode and its significance in biological information processing

Quantum mechanics practiced in the present progressive mode can incorporate into itself the propagation of a signal of a local character. It is possible to view that any movement in the present progressive mode is mutli-agential in the sense of internal interactions due to the absence of an external agency coordinating the global situation simultaneously. The idea of living memory is discussed as carrying the leftover from those actions completed and registered in the present perfect mode and surviving at any present moment. The occurrence of both the signal propagation of a local character and living memory is upheld upon exchange interaction of a quantum mechanical origin. Empirical evidence suggesting the likelihood of such an exchange interaction is found in the neurotransmitter-gated ion channels located on the plasma membrane of the muscle cell in the vicinity of secretory vesicles containing acetylcholine near the nerve terminal. Another case from the empirical evidence is seen in the actomyosin system demonstrating the unidirectional propagation of variations in the acceleration of the displacement of an actin filament sliding on myosin molecules in the presence of ATP molecules.