PubMed · 5704347
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G N Ramachandran, B B Doyle, E R Blout. 1968. Single-chain triple helical structure.. https://doi.org/10.1002/bip.1968.360061213
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The energy-dispersive X-ray reflectometry and turbidity measurements are used to investigate the kinetics of concanavalin A binding onto the distearoylphosphatidylcholine/distearoylphosphatidylethanolamine-+ ++maltobionamide (DSPC/DSPE-mal1) or distearoylphosphatidylcholine/distearoylphosphatidylethanolamine-+ ++maltotetrabionamide (DSPC/mal3) mixed monolayer at the air-water interface. The resulting adsorbed layer of this sugar-binding protein near the membrane with one or three hexoses in the lipid head-group is 3.9 nm or 9.7 nm thick, respectively. The different thicknesses of the adsorbed layer can be correlated with the diverse orientations of the adsorbed proteins. These lay flat on the surface containing DSPE-mal1 and 'perpendicular' to the surface containing DSPE-mal3. The monolayer structure is little affected by concanavalin A binding, but the incorporation of sugar lipids decreases the chain tilt and the interfacial thickness marginally. The binding is quasi-exponential with the time constant between some minutes and several hours depending on the concanavalin A and vesicle concentrations in the bulk. The experimental resolution of the time-resolved measurements made with the laboratory-based instrument is 15 min and the spatial resolution is between 0.05 nm and 0.5 nm, depending on the electron contrast. It is estimated that the high-brilliance synchrotron X-ray source combined with the detection method outlined in this work, could permit the kinetic measurements on the time-scale of < 1 minute.
Hydrophobically modified dextrans, benzoyl dextran and valeryl dextran, have been used to study the interactions between tryptophan residues and benzoyl or valeryl groups by partitioning of tryptophan, tryptophan-tryptophan, (tryptophan)3, poly(lysine, tryptophan), beta-galactosidase and lysozyme in polymer aqueous two-phase systems. The two-phase systems used were polyethylene glycol (PEG)-benzoyl dextran, PEG-valeryl dextran, dextran-benzoyl dextran and dextran-valeryl dextran. Interaction between tryptophan residues and benzoyl or valeryl groups was observed by partitioning of tryptophan containing compounds to the phase containing hydrophobically modified dextran. At a certain phase composition the interactions were increased with increasing number of tryptophan per molecule. In a PEG-dextran system the partitioning of tryptophan peptides to the PEG phase was increased with increased number of tryptophan. In a PEG-benzoyl dextran system the opposite effect was obtained. At similar conditions benzoyl groups showed stronger interactions with tryptophans compared to valeryl groups. The partition coefficient of salts (sodium phosphate, NaCl, Nal and NaClO4) was determined in PEG-benzoyl dextran and PEG-valeryl dextran aqueous two-phase systems. The effect of addition of these salts on partitioning of poly(lysine, tryptophan), beta-galactosidase and lysozyme was studied. Salt effects on partitioning could be explained by the relative affinities of the ions for the polymers in the system. Charged molecules containing tryptophan were to an increasing degree partitioned to the phase for which the counterions had highest affinity. Strong effects on the partitioning of positively charged poly(lysine, tryptophan) and lysozyme were obtained with the ions I- and ClO4-.
Excitable media, which range from autocatalytic chemical systems to biological cells and tissues, can maintain organized structures in the form of rotating spiral waves of excitation. The dynamics of spiral waves in two-dimensional systems have been shown to be susceptible to control by external fields (such as electric, thermal and optical). In three dimensions, the analogues of spiral waves are scroll waves. Here we show that an external field--a temperature gradient--can be used to control a particular class of scroll waves called scroll rings. The gradient allows scroll rings to be precisely oriented in space, and their spontaneous shrinkage to be accelerated, decelerated or even reversed (so that the ring expands). The temperature gradient also influences the lifetimes of the scroll rings. We suggest that these dynamics are likely to be generic to other types of field gradients and other excitable media.