Hajime Honda

Autocatalytic Synthesis of Oligoglycine in a Simulated Submarine Hydrothermal System

A flow reactor simulating a submarine hydrothermal system was constructed for examining the likelihood of oligopeptide synthesis from amino acids alone without recourse to any of condensing agents, templates or metallic ions. We demonstrated that when the initial reactant is glycine, the flow reactor can synthesize both di- and tri-glycine. The initial buildup of the yields of both the oligopeptides was found to be exponential with the elapse of time. The oligopeptide synthesis from glycine in the flow reactor could be autocatalytic.

Hydrothermal circulation of seawater through hot vents and contribution of interface chemistry to prebiotic synthesis

Synthesizing oligopeptides from glycine andalanine in a flow reactor, which stimulates constanthydrothermal circulation of seawater through hot vents onthe primitive Earth, demonstrated that an exponential growthof the products is possible. The initial rapid growth of the product is a consequence of using the products formed inone cycle as the starting materials for the cycle of synthesis.

Prebiotic oligomerization on or inside lipid vesicles in hydrothermal environments.

Oligomerization of amino acids proceeded on or inside lipid vesicles as a model of prebiotic cells in a simulated hydrothermal environment. When the suspension of lipid vesiclestaking up monomeric glycine underwent a sudden temperature dropby traversing from a hot (180 °C) to a cold (0 °C) region repeatedly while circulating through a closedreaction circuit, oligopeptides up to heptaglycine were formed even in the absence of condensing agents.

Synthesizing oligomers from monomeric nucleotides in simulated hydrothermal environments.

Dimers and trimers of adenosine monophosphate(AMP) were synthesized from AMP in environmentssimulating hot vents on the sea floor of the primitiveEarth. The simulated environments were made in the flowreactor, in which an aqueous solution of reactants wascirculated from the hot to the cold region repeatedly. Theoligomerization proceeded most significantly when the hotreaction solution at about 110 °C was abruptly ejected into the cold environment maintained at about 0 °C.

ATP-dependent fluctuations of single actin filaments in vitro

Single filaments of actin were observed to fluctuate in the direction perpendicular to their longitudinal axes when they hydrolyzed ATP in the presence of myosin. The transversal fluctuations of actin filaments were identified by reading the transversal displacements of the filaments under a fluorescence microscope. The transversal fluctuations in the absence of ATP decreased their intensity as the number of myosin molecules contacting directly with actin filaments increased. In the presence of ATP, on the other hand, the amplitude of the transversal fluctuations increased in proportion to the ATP concentration up to a certain level, while the sliding velocity of the filaments did not increase significantly over the same range of ATP concentration. The present observation suggests that the chemical energy released from ATP along actin filament binding to myosin molecules is first and primarily converted into kinetic energy of fluctuations in the form of the displacement movements of the filaments in the direction perpendicular to their longitudinal axes.

Evolving lipid vesicles in prebiotic hydrothermal environments.

We compared three different kinds of lipid vesicles made of saturated fatty acids, unsaturated fatty acids, and phospholipids for their evolutionary capabilities in a simulated hydrothermal environment.Encapsulation of the glycine monomers enhanced the oligomerization of peptides in all cases. Fatty acid vesicles remained stable at higher temperatures and efficiently utilized heat energy for this synthetic reaction. Phospholipid vesicles were destabilized by higher temperatures, and thus were found to be better suited to enhance synthetic reactions at lower temperatures

Phosphorylation of nucleotide molecules in hydrothermal environments

Phosphorylation of AMP into ADP and ATP, that can outrun their hydrolysis, was made possible in a simulated hydrothermal environment when trimetaphosphate was used as the phosphate source. The best yields of phosphorylated products were obtained when the reaction fluids whose temperature was set at about 100 degrees centigrade was injected into the cold environment maintained at 0 degree in a recycling manner. Hydrothermal environments in the primitive ocean could also have served as prebiotic sites for phosphorylation, among others.

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

An actin filament sliding on myosin molecules in the presence of an extremely low concentration of ATP exhibited a staggered movement. Longitudinally sliding movement of the filament was frequently interrupted by its non-sliding, fluctuating movements both in the longitudinal and transversal directions. Intermittent sliding movements of an actin filament indicate establishment of a coordination of ATP-mediated active sites distributed along the filament.

Propagation of a signal coordinating force generation along an actin filament in actomyosin complexes

Abstract Force generation due to ATP hydrolysis by myosin molecules contacting an actin filament was found to be coordinated along the filament. We marked several points along the actin filament with the aid of a fluorescent material, and measured the temporal development of the acceleration of each marked point in the stationary coordinate space. Variations in the acceleration of the sliding movement of the actin filament propagated backward along the filament. Variations in the acceleration propagating in the direction opposite to the direction of the sliding movement show that force generation at each active site of an actomyosin complex could be regulated in a communicative manner along the actin filament.

COMMUNICATIVE INTERACTION OF MYOSINS ALONG AN ACTIN FILAMENT IN THE PRESENCE OF ATP

Myosin molecules contacting an actin filament in the presence of ATP were found to regulate the filamental fluctuations due to ATP hydrolysis in a communicative manner along the filament. As an evidence of the occurrence of the communication, ATP-activated fluctuating displacements of the filament in the direction perpendicular to its longitudinal axis were identified to propagate at a finite velocity not less than about 0.2 micron/s unidirectionally along the filament.