By using measurements of the intensity of light scattered from intact calf lenses, we have determined a number of reagents that induce nuclear and cortical opacification at body temperature. Diffusion of buffered saline solutions of glycerol, other glycols, urea, guanidine hydrochloride or glycine into the lens reverses the opacity of all the reagent-induced cataracts. Similar findings are obtained with lens homogenates, which have gel-like properties as determined from viscosity measurements. A 50 % (by volume) glycerol or 5 M urea solution clarifies human pathologic cataractous lenses by reducing the opacification due to light scattering. These findings suggest that it may be possible, in principle, to reverse human lens cataracts chemically in situ . The scattering of laser light from quasi-periodic lattice of normal lens cells produces a regular diffraction pattern containing many Bragg spots whose positions are those predicted from the basis vectors of the cellular lattice. The intensity of the Bragg reflexions increases greatly when cataracts are formed in the calf and human lens, and falls greatly when the lenses are clarified. The spatial variation in the scattered light intensity of the Bragg spots and between these spots contains detailed information on the structure of the scattering elements associated with opacification.
The structure and thermotropic properties of hydrated l-myristoyl-2-palmitoyl-L-phosphatidylcholine (MPPC) and l-palmitoyl-2-myristoyl-L-phosphatidylcholine (PMPC) have been studied by X-ray diffraction and differential scanning calorimetry (DSC). After prolonged storage at -3 °C, hydrated multilamellar dispersions of both MPPC and PMPC show two endothermic transitions of comparable enthalpies on initial heating. MPPC undergoes transitions at 26 °C (AH = 8.0 kcal/mol of MPPC) and 34 °C (AH = 8.1 kcal/mol of MPPC); PMPC exhibits transitions at lower temperatures, 17 °C (AH = 7.7 kcal/mol of PMPC) and 27 °C (AH = 7.8 kcal/mol of PMPC). For both MPPC and PMPC, only the higher temperature transition is readily reversible; the enthalpy associated with the lower temperature transition is progressively recovered with increasing incubation time at low temperatures, suggesting conversions, albeit kinetically complex, between metastable and stable phases. X-ray diffraction data show the presence of bilayer structures and a similar pattern of structural changes on heating for hydrated (50 wt %) MPPC and PMPC. Below the low-temperature transition a Ahe structure and properties of 1,2-diacyl-L-phosphatidylcholines (PC)1 containing identical fatty acyl chains in the 1 and 2 positions on the glycerol backbone have been studied in detail by a wide variety of biophysical methods. A combination of scanning calorimetry and X-ray diffraction methods has been particularly valuable in describing the thermotropic transitions exhibited by hydrated PCs and elucidating the structural changes accompanying these phase changes. For hydrated 1,2-dipalmitoyl-L-phosphatidylcholine (DPPC) and 1,2-dimyristoyl-L-phosphatidylcholine (DMPC), for example, the two reversible transitions at approximately 35 and 41 °C for DPPC and 13 and 24 °C for DMPC correspond to gel -*gel (Lyz -* PSz) and gel -* liquid-crystal (P^--*• La) bilayer transformations (
Our results suggest that there is an ’’intimate relationship’’ between the Doherty–Benedek–Stephen and Phillies theory for the diffusion coefficient of charged macromolecules. By introducing the hard sphere approximation for the radial distribution function between the macromolecules into the Phillies theory, we obtain a good approximation to the Doherty–Benedek–Stephen result. In order to take into account correlations in the positions of the proteins, we have also introduced the more realistic dilute gas approximation for the radial density function into the Phillies theory. Significantly better agreement with the experimental data has been obtained.
The intriguing diversity of published translational diffusion constants for the fibrinogen molecule can hardly be explained, unless interactions between the molecules are postulated. In the present study we have investigated the possible effect of molecular association and electrostatic intermolecular interactions on the Brownian motion. The translational diffusion coefficient DT, the rotational diffusion coefficient around the minor axis DR and the sedimentation coefficient have been measured. The methods used were dynamic light scattering and analytical ultracentrifugation. The samples were solutions of purified human fibrinogen. The correlation-function corresponding to DT deviates from a single exponential. The initial slope is found to depend on concentration, being DT = (1.7 ± 0.3) 10-7 cm2/s at 10mg/ml, pH 7.4 and 0.15 molar Tris-NaCl, and increases at fibrinogen concentrations below 2mg/ml. These results are compatible with a polydispers solution, in which single molecules are in equilibrium with pair and higher aggregates. The nature of the aggregates is end-to-end as indicated from the difference between the two rotational diffusion constants DR = 40000 ± 20% and DR = 10000 ±30% s-1. On the basis of the Hall-Slayter model and assumption of end-to-end association we calculated the ratio of the sedimentation coefficient of single, pair and triplet associates, being 1:1.14:1.20. Therefore, it is difficult to separate them in a sedimentation run. For ionic strength below 0.05 molar and low fibrinogen concentration (0.lmg/ml) a fast decay appears in the correlation, indicating that the Brownian motion is strongly influenced by electrostatic interactions.
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