鈴木 誠

We have calculated the dielectric relaxation of water around an ion using molecular dynamics simulations. The collective motion of water near the ion showed fast relaxation, whereas the reorientational motion of individual water molecules does not have the fast component. The ratio of the relaxation time for the fast component and the bulk water was consistent with the experimental results, known as hyper-mobile water, for alkali halide aqueous solution.

ATP加水分解反応の量子力学的解析はすでに数十年の歴史があるが、ここでは水中の陽に水分子集団を取り入れてATPの電子状態のゆらぎを考慮したこれまでもっとも精密な量子力学的計算を行った。

It is shown that when a sufficiently large nonpolar solute is inserted into water, the rotational freedom RF of water molecules near the solute is significantly restricted due to the water structuring. When the solute has a moderate surface charge density SCD, in the region adjacent to the solute and in the region within which the solute-water surface separations are close to the molecular diameter of water, the RF of water molecules becomes considerably higher than in the bulk. As the SCD increases, these regions shift slightly more outside with further enhancement of the RF. For sufficiently high SCD, the water molecules in contact with the solute turn largely restrained. It is shown that the appearance of water molecules with anomalously high RF is the most remarkable for a very large solute with high SCD. We argue that the theoretical results are in qualitatively good accord with the experimental observations for the rotational mobility of water molecules near nonpolar side chains of amino acids and F-actin with the domains which are rich in negative charges.

誘電緩和分光法等で測定するイオンの水和特性と対応する溶液化学と分子動力学法をによるイオンの水和自由エネルギー計算を実施し、水和特性のエネルギー論を結び付けようとする研究。

蛋白質周囲の水の情報を検出することで、蛋白質のダイナミクスと機能がより正確に理解できると考えられたためである。この目的のために、以下の個別目標を設定した。（Ａ）蛋白質水和特性解析装置の構築と、蛋白分子周りに分布する水の誘電特性の情報を抽出する方法を開発する。（Ｂ）変性温度の異なるシトクロムc（PA, HT）の誘電スペクトル測定に供しうる量を作製する。（Ｃ）変性温度の異なるシトクロムc（PA, PH, HT, ウマ心筋由来）の水和状態を解析する。（Ｄ）小容量の蛋白水溶液の誘電スペクトルを測定するため、小容量型プローブを設計・試作し、水和解析に応用する。（Ｅ）一分子観察への応用をめざして、蛍光あるいは色素プローブによる溶媒情報抽出法の探索を行う。

Dielectric relaxation (DR) study was performed to reveal the hydration change of Pseudomonas aeruginosa ferric cytochrome c551 (PA c551) in dilute aqueous polutions upon the acid unfolding which undergoes a two-state transition. The DR spectrum of a small spherical region containing a PA c551 molecule and its surrounding water shell was derived from the solution and solvent spectra by dielectric mixture theories. The derived spectrum was well-fitted with a sum of a Debye relaxation component (C1) with a DR frequency around 4.7 GHz and the bulk solvent component (CB). Upon acid unfolding, the DR amplitude of CB decreased with decreasing pH in an inverse manner to that of C1, while the total DR amplitude was almost constant. It indicates that C1 is due to the hydration water of PA c551. Little change in the DR frequency of C1 and a 1.7-fold increase in hydration number were observed.

理研播磨Spring-8 前田雄一郎研究グループとの共同でアクチンthin filamentの水和状態をマイクロ波誘電分光法で調べた。

We investigate the hydration state of horse heart cytochrome c (hh cyt c) in the unfolding process induced by trifluoroacetic acid (TFA). The conformation of hh cyt c changes from the native (N) state (2.9 < pH < 6.0) to the acid-unfolded (UA) state (1.7 < pH < 2.0) to the acid-induced molten globule (A) state (pH ~1.2). Hydration properties of hh cyt c during this process are measured at 20C by high resolution dielectric relaxation (DR) spectroscopy, UVvis absorbance, and circular dichroism spectroscopy.

高分子ゲルと基盤との低摩擦を利用した静電リニアモーターに用いるゲルの摩擦特性測定を行う。

Wediscovered that an amorphous-crystalline transition occurswhena smallamountof water is introduced into an amphiphilic copolymer network consisting of n-alkyl acrylate (n ) 14, 16, 18, 20, 22) and acrylic acid. Differential scanning calorimetry and X-ray diffraction studies show that the dry polymer network is in an amorphous state regardless of the presence of the crystalline moiety. By introduction of water to the polymer network, a crystalline structure attributed to the side-by-side packing of the alkyl chain is formed and the melting temperature of the crystalline increases with the amount of water and saturated to that of homo-n-alkyl acrylate polymers at a water content of 5 wt %. The mechanism of the waterinduced amorphous-crystalline transition is explained in terms of enhanced mobility of the main chain due to hydration of the carboxyl groups of the polymer network.

To gain more structural and functional information on the actomyosin complexes, we have engineered chimera proteins carrying the entire Dictyostelium actin in the loop 2 sequence of the motor domain of Dictyostelium myosin II. Although the chimera proteins were unable to polymerize by themselves, addition of skeletal actin promoted polymerization. Electron microscopic observation demonstrated that the chimera proteins were incorporated into actin filaments, when copolymerized with skeletal actin. Copolymerization with skeletal actin greatly enhanced the MgATPase, while the chimera proteins without added skeletal actin hydrolyzed ATP at a very low rate. These results indicate that the actin part and the motor domain part of the chimera proteins are correctly folded, but the chimera proteins are structurally stressed so that efficient polymerization is inhibited.

Dielectric spectroscopy with microwaves in the frequency range between 0.2 and 20 GHz was used to study the hydration of myosin subfragment 1 (Si). The data were analyzed by a method recently devised, which can resolve the total amount of water restrained by proteins into two components, one with a rotational relaxation frequency (f,) in the gigahertz region (weakly restrained water) and the other with lower fC (strongly restrained water). The weight ratio of total restrained water to Si protein thus obtained (0.35), equivalent to 2100 water molecules per Si molecule, is not much different from the values (0.3-0.4) for other proteins. The weakly restrained component accounts for about two-thirds of the total restrained water, which is in accord with the number of water molecules estimated from the solvent-accessible surface area of alkyl groups on the surface of the atomic model of S1. The number of strongly restrained water molecules coincides with the number of solvent-accessible charged or polar atoms. The dynamic behavior of the S1-restrained water during the ATP hydrolysis was also examined in a time-resolved mode. The result indicates that when Si changes from the Si -ADP sta