Scanning electon microscopy/1980/III.
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Animals↗
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Ultrastructural evidence of the formation of synapses by retinal ganglion cell axons in two nonstandard targets.
After unilateral ablation of the optic tectum in the frog (Rana pipiens), retinal ganglion cell axons enter the lateral thalamic neuropil in large numbers. This area is normally a target of the tectal efferent projection but is not innervated directly from the retina in normal frogs nor in frogs undergoing optic nerve regeneration in the presence of an intact tectum. The ability of retinal axons to form synaptic contacts in this nonstandard target, previously suspected only from light microscope studies, has been ultrastructurally verified in the present investigation. Retinal axon terminals were selectively labeled for light and electon microscope study by introducing horseradish peroxidase (HRP) into the optic nerve 73-413 days after unilateral ablation of the contralateral optic tectum. In some of the frogs, the optic nerve had also been crushed to test the ability of retinal axons regenerating over a long distance to form this connection. The HRP-labeled retinal axon terminals had the same untrastructural morphology whether located in the lateral thalamic neuropil or in the correct regions of projection, e.g., the lateral geniculate complex. They contained clear, spherical synaptic vesicles and made Gray type I synapses on the unlabeled postsynaptic dendrites. The magnitude of the projection was disproportionately greater in animals having complete or nearly complete tectal ablation than in a specimen in which the lesion was significantly incomplete. An aberrant projection was also observed in the nucleus isthmi in some of the specimens. These findings have significance for chemoaffinity theories of the specification of synaptic connections in that the ability of retinal axons to synapse in nonstandard targets in this experimental context may be considered evidence for the expression of appropriate cell-surface recognition-molecules by the abnormally targeted postsynaptic neurons. The likelihood that the expression of these postsynaptic labels is normally repressed transynaptically by molecular signals from the intact tectal input is discussed.
Animals↗
Ultrastructural study of myoepithelial cells in breast carcinoma.
This investigation was designed to study the myoepithelium of the human mammary carcinoma. Tissues were obtained from 30 infiltrating ductal carcinomas. Under light microscope, there were no significant changes noted in the myoepithelium. Glutaraldehyde-fixed tissues were examined under electon microscope. In infiltrating carcinoma the myoepithelial cells contained increased endoplasmic reticulum, abundant microfilaments, secretory granules and intracytoplasmic duct formation. This observation suggests that myoepithelium takes an important and active role in the infiltrating stage of the human mammary carcinoma.
Breast Neoplasms↗
X-ray diffraction and electron microscopy studies of frozen erythrocyte membrane preparations.
Well-defined X-ray diffraction patterns have been recorded from erythrocyte membranes in the frozen state. At -40 degrees C, lamellar periodicities range from 19 to 95 nm depending on the glycerol content (0--40%, respectively). Freeze-fracture electon micrographs of samples frozen in two stages to approximate to the diffraction conditions show ice formation external to membrane stacks. The membrane stacks have periodicities of the same order of magnitude as those obtained by X-ray diffraction.
Differential Thermal Analysis↗
Preparation of unilamellar liposomes of intermediate size (0.1-0.2 mumol) by a combination of reverse phase evaporation and extrusion through polycarbonate membranes.
Liposomes can be prepared by a combination of reverse phase evaporation and sequential extrusion through polycarbonate membranes. The vesicles have diameters in the range 0.05-0.5 micron and are mostly unilamellar as indicated by electon microscopy, capture volume, and availability of reactive groups to periodate oxidation. Sequential extrusion leads to a decrease in the encapsulation efficiency by 2-4-fold, depending upon the lipid composition. The inclusion of cholesterol at a 1 : 1 molar ratio of cholesterol-to-phospholipid increases both the mean size and the size heterogeneity of the liposomes as measured by negative-stain electron microscopy. The mean size of vesicles with an equal molar ratio of cholesterol-to-phospholipid after extrusion through a 0.1 micron membrane is 0.140 micron. Vesicles composed of phosphatidylglycerol/phosphatidylcholine (1 : 4) have a mean size of 0.08 micron after extrusion through a 0.1 micron membrane. The intermediate-size (0.1-0.2 micron) vesicles formed by this process have an aqueous space-to-lipid ratio of 3 : 5 and capture between 12 and 25% of the aqueous phase. The procedure is relatively simple, rapid, and yields almost quantitative recovery of vesicles that encapsulate a large percentage of the total aqueous space.
Carbonates↗
The interaction of 7-substituted actinomycin D analogs with DNA.
The interaction of actinomycin D and three new 7-substituted analogs with calf thymus DNA has been studied by a number of physical techniques. The methods utilized in this investigation include visible absorption spectrometry and ultrafiltration methodology for the determination of equilibrium binding constants; viscometry; and circular dichroism. The studies show that the 7-substituted actinomycin D analogs retain the G . C base pair specific DNA binding demonstrated by actinomycin D. The mode of binding to native DNA, despite substitution at position 7, is practically unaltered. The retention of this binding specificity by these analogs seems to be unaffected by changes in the electon properties of the chromophore.
Animals↗
Photo-initiated ion formation from octaethyl-porphyrin and its zinc chelate as a model for electron transfer in reaction centers.
Ion formation from the reaction of triplet (T) and ground state (P) octaethyl-porphyrin (OEP) and zinc octaethyl porphyrin (ZnOEP) and the corresponding cross-reactions have been measured in dry acetonitrile. A uniquely sensitive and fast conductance apparatus and a pulsed dye laser allowed the measurements to be made at the necessarily very low concentrations of T. The hemogeneous reaction of T (ZnOEP) and P (ZnOEP) occurs with rat constant k(1) = 2.0 x 10(8) M(-1)s(-1) and an ion yield of 67%. The similar homogeneous reaction of OEP has k(2) = 1.3 x 10(8)M(-1)s(-1) but an ion yield of only 3%. The cross-reaction of T (OEP) with P (ZnOEP) has k(3) = 1.5 x 10(8) M(-1)s(-1) and an ion yield of 27%, while the inverse cross-reaction of T (ZnOEP) with P (OEP) has k(4) = 3 x 10(8) M(-1)s(-1) and an ion yield of 20%. Thus, the rate constants are only slightly affected but the yields are sensitive to the porphyrin. The possible formation of the heterogeneous ions ZnOEP+ + OEP-, thermodynamically favored by 0.3 V over the homogeneous ions, has little influence on the observed yields. The data are explained by electron transfer and Coulomb field-electon spin-controlled escape of the initial ion-pair.
Electric Conductivity↗
Ultrastructural abnormalities of liver cells in Reye's syndrome.
Electon microscopic observations were made on liver biopsy specimens from nine infants and children diagnosed as having Reye's syndrome by clinical, laboratory, and light microscopic criteria. In addition to excessive fat content, mitochondrial abnormalities were the most frequent abnormal finding in the liver. However, no correlation could be established between the severity of mitochondrial changes and clinical or biochemical data, and two patients with low levels of the first two urea cycle enzymes showed only mild mitochondrial abnormalities. Nonspecific or artifactual factors have been suggested to explain the mitochondrial changes. However, the data of this study suggest that most of the reported mitochondrial abnormalities are not artifacts, and that they can be helpful in the ultrastructural diagnosis of Reye's syndrome.
Adolescent↗
The structure of the glycocalyx of the golden hamster's peritoneal macrophages following antigen stimulation.
Electon-microscopy was used to study the glycocalyx of peritoneal macrophages from hamsters with transplanted melanotic and amelanotic tumours, and from control animals. The growth of transplantable melanomas in hamsters was found to cause a reduction in the amount of the material stainable with ruthenium red on the surface of the macrophages, as well as changes in the structure of the glycocalyx. The changes were more marked in the case of amelanotic melanomas.
Animals↗
Evidence that carbon monoxide is an obligatory intermediate in anaerobic acetyl-CoA synthesis.
Carbon monoxide is produced by several biological reactions. It is proposed to act as an intracellular signaling molecule and can serve as the carbon and electon source for certain bacteria. Direct evidence for a new biological role for CO is presented here. The results strongly indicate that CO is produced as an obligatory intermediate during growth of the acetogenic bacterium Clostridium thermoaceticum on glucose, H2/CO2, or aromatic carboxylic acids. Our results are consistent with earlier hypotheses of the intermediacy of CO during growth of acetogenic bacteria on CO2 and hexoses [Diekert, G., & Ritter, M. (1983) FEMS Microbiol. Lett. 17, 299-302] and methanogenic Archaea on CO2 [Stupperich, E., Hammel, K. E., Fuchs, G., & Thauer, R. K. (1983) FEBS Lett. 152, 21-23]. Therefore, CO production is a key step in the Wood-Ljungdahl pathway of acetyl-CoA synthesis. The carbonyl group of acetyl-CoA is shown to be formed from the carboxyl group of pyruvate by the following steps. (i) Pyruvate undergoes decarboxylation by pyruvate:ferredoxin oxidoreductase to form acetyl-CoA and CO2. (ii) CO2 is reduced to CO by the CODH site of the bifunctional enzyme CO dehydrogenase/acetyl-CoA synthase (CODH/ACS). (iii) CO generated in situ combines with the ACS active site to form a paramagnetic adduct that has been called the NiFeC species, and (iv) the bound carbonyl group combines with a bound methyl group and CoA to generate acetyl-CoA. To our knowledge, this paper represents the first demonstration of a pathway in which CO is produced and then used as a metabolic intermediate.
Acetate-CoA Ligase↗
Palladium-catalyzed amination of aryl halides on solid support.
[reaction: see text] The first examples of the Pd(0)-catalyzed amination of aryl halides using Rink-resins as nitrogen source are described. Pd(2)dba(3)/BINAP/NaO-t-Bu was found to be the most efficient catalyst/base system, while a solvent mixture of dioxane and tert-butyl alcohol was shown to enhance the selectivity toward the desired monoarylation. Moderate to good yields and excellent purities of the amination products were found with electron-poor aryl halides, while electon-rich aryl halides failed to react under these conditions.
Journal Article↗
Ionic disparity of identical molecules in polymorphs.
[structure: see text] Formation of ionic pairs of identical molecules, extremely common in Nature but exceptional for diffractometric observations in the crystalline state, has been found in one of two polymorphs of a nucleobase analogue, 4,6-pyrimidinedione (1). The occurrence of the neutral and ionic polymorphs of 1 in many respects resembles neutral-ionic transitions of electon-donor/acceptor complexes. The ionization affects the reactivity of 1 and illustrates general properties of H-tautomers with low-disproportionation energy.
Journal Article↗
[Theoretical principles of "contactless" tonometry].
The authors present a short recapitulation of the capabilities of modern applanation tonometry and point out its limitations. They discuss the two methods, "non-contact" and "contactless" tonometry. The latter, which has been recently developed in Hungary, differs from Grolman's in that it employs an electonic system to measure the applanation, which is induced by an air jet. With this method the accuracy of the recording enables events lasting only fractions of a second to be studied in a variety of ways while measurements are being made.
Electronics↗
Quasiclassical study of Eley-Rideal and hot atom reactions of H atoms with Cl adsorbed on a Au(111) surface.
Using quasiclassical methods and a potential energy surface based on total energy calculations, we have found that H atoms react with Cl atoms adsorbed onto a Au(111) surface to produce HCl via Eley-Rideal (ER), hot atom (HA), and Langmuir-Hinschelwood (LH) pathways. We observe two ER mechanisms. At small normal incidence energies reaction results from a more or less direct collision with Cl, leading to a large amount of product vibration (nu=8), and relatively cold rotation and translation. In the second mechanism, more dominant at near-normal incidence and/or large incident energies, the H atom passes near Cl, recoils from the metal, and is pulled into orbit about Cl. This leads to broader product state distributions, and a more even distribution of the 3.0 eV of available energy among the product degrees of freedom, similar to products formed via the HA pathway. Overall, ER processes tend to contribute less than 10% to the reactivity, and most of the HCl is formed via HA processes. There is an increase in HCl formation with surface temperature for both the ER and HA mechanisms, but this increase is relatively weak. We observe typically about 12% H atom sticking, which would lead to HCl formation via a LH process in the experiments, above 140 K. We observe a weak forward scattering due to the direct ER component, as in the experiments. However, unlike the experiments, we observe a dip in our product angular distributions about thetaf=0 degrees, which we ascribe to our quasiclassical approximation. While we tend to see more energy in the hot products than in the experiments, our product translational, rotational, and vibrational distributions are in relatively reasonable agreement with those measured. One major disagreement with experiment is that there is apparently a significant sticking of the H atom at low temperatures, leading to a large LH component. In addition, the ER and HA components increase much more strongly with temperature than in the calculations. It is possible that electon-hole pair excitations in the metal strongly relax both the H atom and the excited HCl molecules formed.
Journal Article↗
Lipid degeneration in pheochromocytomas mimicking adrenal cortical tumors.
A case of bilateral adrenal pheochromocytomas with unusual morphologic features is reported in a 27-year-old man with a family history of von Hippel-Lindau disease. In both glands, the medulla was replaced by neoplasms with two distinct gross and microscopic appearances. There was typical pheochromocytoma in areas of dusky red tissue. The yellow nodules noted on gross examination were microscopically composed of large cells with vacuolated cytoplasm. Fat stains confirmed the presence of lipid in these areas. Immunohistochemistry revealed positivity for neuron-specific enolase and chromogranin in the cytoplasm of pheochromocytes, as well as in the perinuclear cytoplasm and processes of cells scattered in the yellow nodules. Ultrastructural examination of the yellow lesions showed characteristics of pheochromocytoma and an extensive accumulation of lipid. Although gross and light-microscopic examination of the yellow tissue suggested adrenal cortical nodules, immunohistochemistry and electon microscopy elucidated lipid degeneration within pheochromocytoma, a finding not previously described.
Adrenal Cortex Neoplasms↗
Macrophages of the bovine heifer mammary gland: morphological features during initiation and resolution of the inflammatory response.
This work characterizes macrophage morphological features during initiation and resolution of an inflammatory response by the bovine mammary gland. The study has been carried out in 20 mammary glands of five virgin heifers by using light microscopy of natural and stained cells and by using transmission electron microscopy (TEM). The inflammatory reaction was induced by an intramammary administration of phosphate-buffered saline (PBS). It has been found that both the initial as well as the resolution phases of the inflammatory reaction are characteristic of the presence of various morphologically different macrophage forms. During the initial phase of the inflammatory response, the major proportion of the macrophage population consisted of monocyte-like macrophages, which represented newly migrated cells. These macrophages were 12-15 mum in size, with spherical or ovoidal shapes, and contained homogenous, fine-granular cytoplasm rich in Golgi complexes, numerous mitochondria, and no lysosomes. The nuclei of the macrophages were kidney-shaped, and surrounded by dark chromatin along the peripheries. Macrophages with phagocytosed apoptotic neutrophils in the cytoplasm were detected already during the initial phase. These macrophages reached the highest proportion 48-72 h after the influx induction and participated in the resolution of the inflammatory reaction. Other cells, also detected during the resolution of the inflammatory reaction, were vacuolized macrophages that formed the largest cells in the lavages of the mammary glands and that were structurally characteristic for the presence of vacuoles in the cytoplasm. In TEM the macrophage vacuoles formed both phagolysosomes with residues of pre-digested material of phagocytosed apoptotic neutrophils and vacuoles that were less electon-dense. Morphologically different forms of macrophages reflected their real-time functions in the inflammation process.
Animals↗
Structure of the regular surface layer of Aquaspirillum serpens MW5.
The structure of the regular surface layer of Aquaspirillum serpens MW5 has been investigated by electon microscopy supplemented by computer image processing and least-squares analysis. The layer has a ribbed appearance, both on the bacterium and in isolated, negatively stained fragments. However, detailed analysis indicated that the layer was composed of two hexagonal sheets having p6mm symmetry and a = 16 nm. One sheet was staggered by one half repeat along a (1,0) line of the p6nm lattice relative to the second so that, in projection, the pattern of the composite layer was a translational moiré, characterized by a series of ribs spaced 16 nm apart. The ribbed layer had cmm symmetry with a = 32 nm and b = 18.5 nm. Analysis of this pattern indicated that the two p6nm hexagonal sheets were unevenly stained, and this was confirmed by using least-squares methods to simulate the observed pattern by combining two hexagonal patterns. The general structure of the layer was consistent with a role as a selective and protective barrier on the cell surface.
Cell Membrane↗
Effect of oxygen on heme and porphyrin accumulation from delta-aminolevulinic acid by suspensions of anaerobically grown Staphylococcus epidermidis.
The effect of various conditions on the accumulation of porphyrins and heme by resting suspensions of anaerobically grown cells of Staphylococcus epidermidis was examined. Anaerobically grown cells contain 10 to 15% of the amount of protoheme found in cells grown aerobically. Resting suspensions of anaerobically grown cells, when incubated aerobically in buffer with delta-aminolevulinic acid and glucose for 60 min, exhibited a fourfold increase in protoheme content. At high levels of delta-aminolevulinic acid, there was also a significant accumulation of porphyrins with the solubility and chromatographic properties of coproporphyrin and uroporphyrin. Protoporphyrin was not accumulated. When oxygen was excluded from the incubation mixture, accumulation of protoheme was prevented, but accumulation of coproporphyrin and total porphyrin was enhanced. Nitrate served as an electon acceptor as indicated by its reduction to nitrite; however, nitrate did not substitute for oxygen in causing the accumulation of protoheme. These results suggested that oxygen is required for one of the late steps of heme synthesis in S. epidermidis, possibly for the conversion of coproporphyrinogen to protoporphyrin. The inability of nitrate to substitute for oxygen suggests a role for molecular oxygen as a substrate rather than as an electron acceptor for heme synthesis.
Chromatography, Thin Layer↗