PubMed · 1229378
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S Peter, R L Steere. 1975. [Complementary fracturing in freeze etching].. https://pubmed.ncbi.nlm.nih.gov/1229378/
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Thermodynamically stable vesicle (L(alpha1)) formation from glycolipid biosurfactant sponge phase (L(3)) and its mechanism were investigated using a "natural" biocompatible mannosyl-erythritol lipid-A (MEL-A)/L-alpha-dilauroylphosphatidylcholine (DLPC) mixture by varying the composition. The trapping efficiency for calcein and turbidity measurements clearly indicated the existence of three regions: while the trapping efficiencies of the mixed MEL-A/DLPC assemblies at the compositions with X(DLPC)< or =0.1 or X(DLPC)> or =0.8 were almost zero, the mixed assemblies at the compositions with 0.1 or =0.8 were multilamellar vesicles (L(alpha)) with diameter from 2 to 10 microm. Meanwhile, dynamic light scattering (DLS) measurement revealed that the average size of the vesicles at the composition of X(DLPC)=0.3 was 633.2 nm, which is remarkably small compared to other compositions. Moreover, the mixed vesicle solution at the composition of X(DLPC)=0.3 was slightly bluish and turbid and kept its dispersion stability at 25 degrees C for more than 3 months, indicating the formation of a thermodynamically stable vesicle (L(alpha1)). These results exhibited the formation of a thermodynamically stable vesicle (L(alpha1)) with a high dispersibility from the MEL-A/DLPC mixture. The asymmetric distribution of MEL-A and DLPC in the two vesicle monolayers caused by the difference in geometrical structures is very likely to have changed their self-assembled structure from a sponge phase (L(3)) to a thermodynamically stable vesicle (L(alpha1)).
Freeze fracture direct imaging (FFDI) has been used to image microstructures present in a highly viscous four-component mesophase containing water, isooctane, AOT [bis(2-ethylhexyl) sodium sulfosuccinate], and lecithin. As water is added to a fixed amount of a ternary solution of isooctane and the two surfactants, the microstructure evolves from a water-in-oil microemulsion, to a highly viscous columnar hexagonal, and then to multilamellar vesicles. Each of these microstructures is imaged directly. Previous small-angle neutron scattering measurements have identified the lamellar phase, but the FFDI technique demonstrates that these are onionlike curved multilamellar structures rather than planar bilayers. Freeze fracture direct imaging expands the range of cryo-transmission microscopy to highly viscous, high-organic-content systems that typically have been difficult to visualize.
Mycoplasma mobile is a flask-shaped bacteria that binds to a substrate and glides towards its tapered end, the so-called "head-like protrusion," by an unknown mechanism. To search for cellular structures underlying this motility, the cell-substrate interface of actively gliding cells was visualized by rapid-freeze-and-freeze-fracture rotary-shadow electron microscopy. Novel structures, called "spikes," were observed to protrude from the cell membrane and attach to the glass surface at their distal end. The spikes were on average 50 nm in length and 4 nm in diameter, most abundant around the head, and not observed in a nonbinding mutant. The spikes may be involved in the mechanism of binding, gliding, or both.