Geoffrey Rapp

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By means of x-ray diffraction we show that several sodium salts and the disaccharides sucrose and trehalose strongly accelerate the formation of cubic phases in phosphatidylethanolamine (PE) dispersions upon temperature cycling through the lamellar liquid crystalline-inverted hexagonal (Lalpha-HII) phase transition. Ethylene glycol does not have such an(More)
Collagen type I is among the most important stress-carrying protein structures in mammals. Despite their importance for the outstanding mechanical properties of this tissue, there is still a lack of understanding of the processes that lead to the specific shape of the stress-strain curve of collagen. Recent in situ synchrotron X-ray scattering experiments(More)
By using time-resolved X-ray diffraction we demonstrate that low amounts (5-10 mol%) of a phospholipid with two saturated hydrocarbon acyl chains 14 carbon atoms long and PEG550 chain covalently attached to its phosphoethanolamine polar head group, DMPE(PEG550), induce spontaneous formation of a cubic phase with lattice constant 20.5 nm (cubic aspect #8,(More)
Single muscle fibers at 1 degreesC were subjected to brief tetani (20 Hz) at intervals of between 20 s and 300 s over a period of up to 2 h. A band lattice spacing increased during this period at a rate inversely dependent on the rest interval between tetani. Spacing increased rapidly during the first 10 tetani at a rate equivalent to the production of 0.04(More)
Crystals of Ha-Ras p21 with caged GTP at the active site have been used to investigate the conformational changes of p21 on GTP hydrolysis. The structure of the short-lived p21.GTP complex was determined by Laue diffraction methods. After GTP hydrolysis, substantial structural changes occur in the parts of the molecule implicated in the interaction with(More)
Ceramide has recently been established as a central messenger in the signaling cascades controlling cell behavior. Physicochemical studies have revealed a strong tendency of this lipid toward phase separation in mixtures with phosphatidylcholines. The thermal phase behavior and structure of fully hydrated binary membranes composed of(More)
The temperature dependence of the pressure-induced equilibrium unfolding of staphylococcal nuclease (Snase) was determined by fluorescence of the single tryptophan residue, FTIR absorption for the amide I' and tyrosine O-H bands, and small-angle X-ray scattering (SAXS). The results from these three techniques were similar, although the stability as measured(More)
Collagen is the most abundant structural protein in vertebrates. The specific shape of its stress-strain curve is crucial for the function of a number of organs. Although the macroscopic mechanical behavior of collagen is well known, there is still no explanation of the elastic process at the supramolecular level. We have performed in situ synchrotron x-ray(More)
The pressure-induced unfolding of wild-type staphylococcal nuclease (Snase WT) was studied using synchrotron X-ray small-angle scattering (SAXS) and Fourier-transform infrared (FT-IR) spectroscopy, which monitor changes in the tertiary and secondary structural properties of the protein upon pressurization. The experimental results reveal that application of(More)
Gutta-percha endodontic filling points were found to contain approximately 20% gutta-percha (matrix), 66% zinc oxide (filler), 11% heavy metal sulfates (radiopacifier), and 3% waxes and/or resins (plasticizer). The mechanical properties were indicative of a partially crystalline viscoelastic polymeric material. They were found to obey Hooke's law and(More)