Lamellar Profiles Research Articles

Structural aspects of the interaction of bee venom peptide melittin with phospholipids.

AbstractIn aqueous solution, melittin structure, investigated by CD and 1H‐nmr, depends on pH and ionic composition, which also regulate the aggregation state of the peptide. When interacting with phospholipids, however, melittin exhibits a right‐handed helical conformation without any evidence of oligomeric association. The overall bilayer structure of phospholipid aqueous dispersions is also maintained in the presence of melittin, although the permeability to aqueous solutes is considerably increased. Small‐angle neutron‐diffraction analysis of oriented multilayers confirms the existence of a lamellar profile, despite the presence of the peptide throughout each bilayer and exchangeable protons almost reaching the center of the hydrophobic alkyl chains region.

The effects of iron and light treatments on chloroplast composition and ultrastructure in iron‐deficient barley leaves

Abstract The fine structure and major biochemical fractions of iron‐deficient chloroplasts from Hordeum vulgare were examined. Electron micrographic studies of the isolated chloroplasts revealed reduced plastid areas, as well as, reduced thylakoid lamellar profiles. Biochemical analysis of the isolated plastids showed iron involvement in both protein and chlorophyll contents.

On the morphology of melt-crystallized polyethylene - I. Lamellar profiles

The morphology of melt-crystallized polyethylene has been surveyed, and it has been revealed that all specimens are highly lamellar. Classifi­cation of the textures is possible in terms of the lamellar profiles in b -projection, i. e. down the radii of spherulites. For polyethylene crystal­lized as the orthorhombic phase only three types of lamellar profile have been observed for readily accessible growth conditions. There are ridged sheets of alternating {201} facets, planar {201} sheets and S-shaped sheets which are, to a first approximation, derivable from {201} platelets by shear of the lateral regions displacing {100} parallel to c . It is possible, moreover, to distinguish between the first-forming or dominant lamellae which lay down the framework of the texture and the later-forming or subsidiary lamellae which fill the framework. Dominant lamellae may have ridged, planar or S-shaped profiles but subsidiary lamellae appear only ridged or planar. Ridged dominant sheets form under régime I conditions as a consequence of distinct facets on the growth front. The association of ridges and growth facets indicates regularity in folding. S-shaped sheets are usually dominant in régime II growth. They appear to have been deformed from planar {201} sheets by forces associated with the forma­tion of banded spherulites.

On the morphology of melt-crystallized polyethylene - II. Lamellae and their crystallization conditions

The microstructure of melt-crystallized linear polyethylene has been correlated with the variables of crystallization for most readily attainable conditions. All samples are filled with well defined lamellae with an aver­age chain inclination of about 35° to lamellar normals. The lamellar thickness depends upon supercooling rather than directly on crystalliza­tion temperature, which indicates that it is a kinetically determined quantity. The simple assumption that it is a constant multiple of the height given by secondary nucleation is, however, incorrect. Lamellar profiles depend only upon the crystallization temperature and molecular mass of the polyethylene concerned. They are independent of the extent of spherulitic development and are not determined solely by the kinetic régime in which crystals grow. Dominant S-shaped lamellae (Ss) and their associated subsidiary platelets are, nevertheless, the prevalent form for crystallization within régime II, i. e. in most cases of practical import­ance. The distinction between dominant and subsidiary lamellae is linked to fractional crystallization. At low supercoolings it is shown that shorter molecules are concentrated within subsidiary lamellae, and the trend to separate later-crystallizing species is likely to persist, to a lesser degree, even to quenched samples. With the use of added branched molecules this has been demonstrated to occur. The consequences of spatial segre­gation are likely to include increased vulnerability to mechanical and environmentally induced failure.

Aurosomes produced by sodium chloroaurate

Aurosomes were produced in the rabbit synovial membrane by injecting sodium chloroaurate. They contained electron-dense, filamentous, rod-like and lamellar profiles studded with particles and granules. These aurosomes are morphologically indistinguishable from aurosomes produced by sulphur-containing soluble gold salts such as sodium aurothiomalate and aurothioglucose. It is therefore concluded that the sulphur-containing portion of these molecules is not responsible for the characteristic morphology of the aurosome as claimed by others. However, electron-probe x-ray analysis of aurosomes produced by sodium chloroaurate showed the presence of gold, phosphorus and sulphur. It is concluded that the sulphur and phosphorus must have been derived from the biological milieu, since it could not have been derived from the injected compound.

Further observations on spermiogenesis in the shrimp, Crangon septemspinosa. A mechanism for cytoplasmic reduction

In the shrimp (Crangon septemspinosa), spermatid production and storage occur within an extensive syncytium. Reduction of this syncytium results from the reorganization of syncytial materials into elaborate tubuloreticular and lamellar membrane profiles which enclose granular inclusions and mitochondria. In this study, these configurations are referred to as cytoplasmic reduction complexes (CRC) and are present throughout the region of the testes undergoing stage 4 of spermiogenesis. The vacuolated appearance of this segment of the testes is the result of CRC formation. Further reduction of the syncytium and syncytial complexes proceeds according to their relationship with nurse cells. The tubuloreticulum of complexes located near nurse cells is transformed into multilaminate membrane whorls which, subsequently, are phagocytosed by nurse cells. In contrast, the complexes and associated vacuoles not related spatially to nurse cells are further reduced to irregular membrane profiles and paracrystalline lattices. The possible functional significance of these membranous inclusions is discussed.

X-ray gratings: the GMS mount

Using rigorous electromagnetic theory, the interest of the specific off-plane mounting for x-ray gratings is discussed in detail. The optimization of the blaze angle for ruled gratings is considered, as well as the extension of the mounting to sinusoidal and lamellar profiles.

Mitosis in rat thyroid epithelial cells in vivo: I. Ultrastructural changes in cytoplasmic organelles during the mitotic cycle

The ultrastructure of mitosis was studied in polarized, well-differentiated thyroid epithelial cells in vivo following stimulation with the goitrogen, thiouracil, and attention was focused on changes occurring in cytoplasmic organelles. RER cisternae appeared from mid-prometaphase to mid-telophase to undergo a vesicular transformation from lamellar profiles to smaller, rounder profiles with an up to 60% lower concentration of bound ribosomes. The Golgi apparatus underwent a nearly parallel breakdown/reformation process, and Golgi remnants were frequently associated with large clouds of smooth-surfaced 70-nm-diameter vesicles. Apical vesicles, believed to contain thyroglobulin, were found to accumulate during mitosis, reaching about six times their interphase concentration by mid-telophase, when they were observed in large clusters about the spindle poles. Clusters of apical vesicles then appeared to migrate to their usual apical location. Changes in the distribution of lysosomes were noted in late prometaphase, when they became aggregated into clusters, and in early telophase when they accumulated near the cleavage furrow.

Mental retardation, hypotonia, and generalized seizures associated with astrocytic “residual” bodies: An ultrastructural study

Two siblings suffering since birth from convulsions, hypotonia, and mental retardation are presented. In the older sibling (eight and one-half years of age) frontal lobe biopsy revealed abnormal cytosomes with lamellar profiles in astrocytes, macrophages, and to a lesser degree in neurons. Similar cytosomes have not yet been reported in cases of sphingolipidoses or in late infantile-juvenile amaurotic idiocy. These cytosomes stained intensely with silver proteinate, an ultrastructural cytochemical stain for carbohydrate moieties. In contrast, lipofuscin did not stain with silver proteinate. Multilamellar (crescentic curvilinear) cytosomes from a reported case of late infantile amaurotic idocy (Batten-Vogt-Spielmeyer disease) did not stain with silver proteinate. Abnormal cytosomes were not found in blood cells, liver, and peripheral nerve. In the younger sibling (14 months old) postmortem ultrastructural studies of cerebral tissue showed very few abnormal cytosomes. On the basis of the clinical and ultrastructural findings, we conclude that these two cases can be distinguished from those with multilamellar (crescentic-curvilinear) inclusions and from cases of the so-called “neuronal ceroid-lipofuscinosis” syndrome.

Cytochemistry of acid mucosubstance and acid phosphatase in Cryptococcus neoformans.

At the ultrastructural level, dialyzed iron stains only the mucoid capsule in Cryptococcus neoformans, converting it from the most lucent to an extremely dense layer and thus demonstrating its content of acid mucosubstance. After lead staining of thin sections of dialyzed iron treated specimens, the wall exhibits a dense inner and translucent outer layer. The inner layer and mucoid capsule appear thicker in the mother than the daughter cell of budding organisms. C. neoformans cells fixed in suspension and incubated in acid phosphatase substrate medium exhibit at the ultrastructural level activity confined to the mucoid capsule, cell wall, and internal extensions presumed to be plasmalemmasomes. Organisms in small blocks or cryostat sections of pellets fixed in clotted fibrin, when incubated for acid phosphatase, reveal moderate to no reactivity in cell wall and mucoid capsule but strong activity in surrounding fibrin aggregates. In the latter specimens, reaction product indicative of acid phosphatase also is evident in the nuclear envelope, in some of the profiles of presumed granular reticulum, in complex lamellar profiles presumed to be Golgi elements, and in small cytoplasmic bodies and large vacuoles. The morphological specimens disclose counterparts of acid phosphatase reactive structures and show lucent cytoplasm segregated by circular mitochondrial profiles and a difference between the thickness and density of the plasmalemma and other cell membranes.

Hypertrophy of liver cell smooth surfaced reticulum following progesterone administration.

Progesterone given daily for several days to male golden hamsters was shown to promote an increase in liver weight and a striking increase in hepatic smooth endoplasmic reticulum. This increase in smooth reticulum observed by electron microscopy was confirmed biochemically through microsomal phospholipid measurements. The alterations in liver structure brought about by administration of progesterone are comparable to those induced by phenobarbital. Hypertrophy of the smooth reticulum is seen in the form of a delicate system of interwoven tubules which freely anastomose and often are seen in confluence with the lamellar profiles of rough reticulum. Progesterone-induced hypertrophy of the hepatic smooth endoplasmic reticulum demonstrates that this organelle is responsive to an endogenous compound normally present in the circulation, and suggests that stimulation by steroids may be responsible in part for the maintenance of microsomal hydroxylases and smooth reticulum in the normal hepatic cell.

Mechanisms of protein yolk synthesis and deposition in crustacean oocytes

Electron microscope studies on the oocytes of several crustacean species demonstrate that the protein yolk arises within vesicular and lamellar forms of the rough-surfaced endoplasmic reticulum. The vesicular form of the endoplasmic reticulum may have its origin from a blebbing process of the outer layer of the nuclear envelope. Disc-shaped granules, representing precursor elements of the yolk granules, appear within the vesicular and lamellar profiles of endoplasmic reticulum. Autoradiographic results suggest that the ribosomes attached to the endoplasmic reticulum take part in the biosynthesis of yolk proteins. Numerous disc-shaped granules accumulate within the cisternae of the endoplasmic reticulum, but eventually they undergo a transformation into a finely granular yolk granule. Thus, both the origin and growth of protein yolk granules occur within membranes constituting the endoplasmic reticulum. The results provide evidence that intra-ooplasmic synthesis of yolk protein occurs in these oocytes.