Thermodynamic and kinetic studies of macromolec structure and enzymic mechanisms

(i)对淀粉样肽和蛋白质结构的光学研究仍在继续，我们特别感兴趣的是与淀粉样纤维的交叉β结构相关的非常强的CD光谱的起源。这种现象由肽显示，所述肽已显示形成具有平行和反平行β折叠结构的淀粉样蛋白。 (ii)与T. K.戴耶和B。Chen（Univ. of MD）的研究中，我们研究了在增加浓度的代谢物S-腺苷甲硫氨酸（SAM）和Mg++存在下，小的惰性共溶质氧化三甲胺（TMAO）对SAM II核糖开关构象变化的影响。认为游离核糖开关在不存在SAM和Mg++的情况下处于开放或半随机构象，并且在结合SAM和/或Mg++后变得更加折叠和紧凑。广泛的测量依赖的圆二色性光谱的核糖开关后，这些小的配体的浓度可以定量占的模型，根据SAM绑定到一个紧凑的构象。在没有SAM的情况下，核糖开关似乎是开放和紧凑状态的混合物。低浓度的Mg++或TMAO与开放形式结合，抑制SAM的结合。在较高浓度下，Mg++的协同结合或TMAO的分子拥挤，将核糖开关转化为紧凑形式，促进SAM的结合。Mg++的进一步结合增加了核糖开关的紧凑形式对SAM的亲和力。水动力学测量表明，核糖开关被浓缩的TMAO压实。 (iii)碳纳米管结构的光学研究。

(i) Optical studies on the structures of amyloid peptides and proteins are continuing.We are particularly interested in origin of the very intense CD spectrum which has been associated with the cross-beta structure of amyloid fibrils. This phenomenon is shown by peptides which have been shown to form amyloid with both parallel and anti-parallel beta sheet structure. (ii) In collaboration with the group of T. K. Dayie and B. Chen (Univ. of MD), we have investigated the effect of a small inert cosolute, trimethylamine oxide (TMAO), on the conformational changes of the SAM II riboswitch in the presence of increasing concentrations of the metabolite S-adenosyl-methionine (SAM) and Mg++. The free riboswitch was thought to be in an open or semi-random conformation in the absence of SAM and Mg++ and to become more folded and compact upon binding SAM and/or Mg++. Extensive measurements of the dependence of circular dichroism spectra of the riboswitch upon the concentrations of these small ligands may be quantitatively accounted for by a model, according to which SAM binds exclusively to a compact conformation. In the absence of SAM, the riboswitch seems to be a mixture of open and compact states. Low concentrations of Mg++ or TMAO bind to the open form(s), inhibiting the binding of SAM. At higher concentrations, cooperative binding of Mg++ or molecular crowding by TMAO, transform the riboswitch into the compact form, facilitating the binding of SAM. Further binding of Mg++ increases the affinity of the compact form of the riboswitch for SAM. Hydrodynamic measurements show that the riboswitch is compacted by concentrated TMAO. (iii) Optical studies on the structure of carbon nanotubes.