The phase diagram of the ternary surfactant system tetradecyldimethylamine oxide/heptanol/water is reported for small surfactant concentrations. With increasing cosurfactant/ surfactant ratio X, the generally observed sequence of the phases Li, La, and L3 is found. These single phases are separated by narrow two-phase regions. Detailed investigations show however that the wide L"-phase region consists of at least two subphases, a L«i and a L"h phase which have different macroscopic properties. Freeze fracture electron micrographs which were produced from the Lai phase show clearly multilamellar vesicles which have large holes in their bilayers and are therefore called "perforated vesicles". For small surfactant concentrations around 50 mM, two more isotropic phases are observed besides the Li and L3 phases which are called Li* and L3*. Electron micrographs of the L3 phase show that it consists of continuous bilayers which form a three-dimensional multiply connected network with saddle-shaped structures. Typical for the micrographs are fractures across the tubular bilayers, resulting in oval-shaped patterns. The images furthermore show that the preferred fracture of the L3 phase follows the midplane of the bilayer. The electron micrographs of the L3 phase are reported for concentrations between 50 and 400 mM. The photos show that the typical length scale of the L3 phase, that is, the average diameter across a tubular structure, is of the same size as the interlamellar spacing in the neighboring La phase and varies inversely with the volume fraction of the surfactant (d *=~1 2345). The bilayers in the L3 phase and the La phase which in some cases were produced in the preparation process for freeze fracturing were generally very flat on a local scale and showed no undulations on a microscopic level. The phase boundary between the La and the L3 phases was very sharp and smaller than the length scale of the L3 phase. Electric birefringence data which were obtained on the L3 phase show that both the amplitude and the time constant follow simple scaling laws. The relaxation time is inversely proportional to the third power of the volume fraction while the amplitude is inversely proportional to the second power.

Summary In this study preileal starch digestibility of starchy feeds (oats, corn, barley, potatoes, manioc) was determined in seven jejunofistulated horses. The grains were fed whole (oats, corn), rolled (oats, barley), crushed, ground and expanded (corn); the potatoes were fresh, the manioc rolled. Ground corn was also fed in combination with amylase. The feeds were fed partly isolated or in combination with alfalfa meal or hay (Table 1). At least four horses with a cannula in the terminal jejunum were used for each diet. Two meals per day were offered at 12 h intervals. The starch intake was mostly about 2 g/kg bw/meal, except one period with oats (3.9 g starch/kg bw) and with expanded corn (1.4 g/kg bw). Jejunal chyme was postprandially collected 11 times (from 1st to the 11th h after the morning meal for 15 min). Starch was determined polarimetrically. The preileal digestibility of starch was calculated by the marker method (chromic oxide 0.25% DM) and by estimating the total jejunoileal chyme flow during 12 h postprandially extrapolating the sample volume from the 15 min sampling periods. The results of both methods agreed quite well. Preileal digestibility of oat starch (80–90%) was (independent of doses or preparation or of the combination with hay, Table 4) significantly higher than that of whole or crushed corn (30%) or barley (26%). Grinding of corn significantly increased preileal digestibility to 51%, expanding to 90%. The addition of amylase improved digestion of ground corn by 10% (absolute). The preileal digestibility of potato or manioc was less than 10%. Individual factors in the horse (chewing intensity, amylase activity) had also considerable influence on preileal starch digestibility.

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The peptide sequence B18, derived from the membrane-associated sea urchin sperm protein bindin, triggers fusion between lipid vesicles. It exhibits many similarities to viral fusion peptides and may have a corresponding function in fertilization. The lipid-peptide and peptide-peptide interactions of B18 are investigated here at the ultrastructural level by electron microscopy and x-ray diffraction. The histidine-rich peptide is shown to self-associate into two distinctly different supramolecular structures, depending on the presence of Zn(2+), which controls its fusogenic activity. In aqueous buffer the peptide per se assembles into beta-sheet amyloid fibrils, whereas in the presence of Zn(2+) it forms smooth globular clusters. When B18 per se is added to uncharged large unilamellar vesicles, they become visibly disrupted by the fibrils, but no genuine fusion is observed. Only in the presence of Zn(2+) does the peptide induce extensive fusion of vesicles, which is evident from their dramatic increase in size. Besides these morphological changes, we observed distinct fibrillar and particulate structures in the bilayer, which are attributed to B18 in either of its two self-assembled forms. We conclude that membrane fusion involves an alpha-helical peptide conformation, which can oligomerize further in the membrane. The role of Zn(2+) is to promote this local helical structure in B18 and to prevent its inactivation as beta-sheet fibrils.