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Some humorous suggestions for what to do about the discrepancy between certain chemical names and symbols.

Individual head and neck carcinomas show extreme regional cellular differentiation. Some cells are rich in keratin filaments (T cells) and some have little keratin and a high density of free ribosomes (R or RT cells). We attempted to isolate these two cell types in order to test their relative invasiveness in an in vitro model. The high frequency of mitosis of hyperkeratinized cells showed that there was no constraint on the motility of cell division. High-voltage electron microscopy of serial thick sections and three-dimensional graphic reconstruction demonstrated that keratin cytoskeleton filaments were cross-linked into short, thick bundles. However, the keratin cytoskeleton was absent from some portions of the cytoplasm. In normal differentiated keratinized cells, a more uniform spanning of the whole cell by thin keratin intermediate-filament bundles was evident. The cytoplasm may be more mobile in the keratinized tumor cells. Even heavily keratinized T cells, like the less keratinized cell types, may have invasive motility.

SUMMARY Levels of impairment of electron-microscopic images of biological specimens stemming from radiation damage are assessed in a rapid visual procedure that involves taking a pair of low-fluence micrographs of a specimen area before and after a fraction of the picture area has been more seriously damaged by applying a measured electron fluence. The pair of micrographs is treated as a mock-stereo pair and is given contrasting colours. Lateral displacements of specimen details appear as false relief and changes in electron lucency as false colour.

Methods Water samples were analyzed for asbestos with a transmission electron microscope (TEM) using the interim US Environmental Protection Agency (USEPA) methodology.2 Water samples were filtered through 0.1-/xm-pore polycarbonate filters, and the filter surfaces were then carbon-coated in a vacuum evaporator. Sections were cut from the filters and placed on TEM grids in a chloroform atmosphere so that the filter dissolved, leaving a carbon film with trapped particles on the grid. These were examined at 20,000x and asbestos fibers positively identified by electron High concentrations of asbestos were found in the water supply system of Woodstock, N.Y., following a routine pipe-tapping operation in the fall of 1985. Analysis of a water sample collected 10 days after tapping showed asbestos concentrations in excess of 104 million fibers per litre (MFL). The source of this asbestos was asbestos-cement (AC) pipe, which was so deteriorated that sections of pipe could be easily broken by hand. Although asbestos concentrations decreased rapidly as AC pipe was removed from the system, concentrations as high as 49 MFL were measured during the summer of 1986. Throughout the sampling period, even when concentrations fell below 1 MFL, Woodstock water samples were characterized by fibers with much larger lengths, widths, and masses than those collected in nonproblem areas across New York state.

SUMMARY A user evaluation has been made by electron microscopists of an X-ray film for routine electron microscopy. The recent improvements in mammographic X-ray films, with the attempt to reduce the patient dose required to produce a high-resolution mammogram, have resulted in some useful films for medium- and high-voltage electron microscopy. They can yield essential cytological information with a reduction of the electron fluence (exposure) applied to the specimen of more than an order of magnitude compared with conventional electron-microscope films. Their use is indicated in situations where beam damage is severe.

Asbestos contamination in excess of 10 billion fibers per liter was detected in a community's drinking water. To assess the possibility of waterborne asbestos becoming airborne, air samples were collected from impacted houses receiving contaminated water from three control houses. Collected within each house were three samples on 0.6-micrometer-pore Nuclepore filters and three samples on 0.8-micrometer-pore Millipore filters. In addition, bulk samples of suspect material and water samples were collected. Mean waterborne asbestos concentrations were 24 million fibers per liter (MFL) in the impacted houses versus only 1.1 MFL in the control houses. Transmission electron microscopy revealed that airborne asbestos concentrations were highest in impacted houses, with airborne asbestos concentrations positively correlated with waterborne concentrations. For fiber and mass measurements on both filter types, airborne asbestos concentrations were significantly higher in the impacted houses: mean concentrations in impacted houses were 0.12 fibers/cm3 and 1.7 ng/m3 on Nuclepore filters and 0.053 fibers/cm3 and 2.3 ng/m3 on Millipore filters versus only 0.037 fibers/cm3 and 0.31 ng/m3 on Nuclepore filters and 0.0077 fibers/cm3 and 0.14 ng/m3 on Millipore filters from control houses. Also detected in the air samples from impacted houses were clusters of chrysotile, often with several hundreds of fibers. When estimates of these individual fibers were added to the total fiber count, the difference between the impacted and control houses became even greater. The increased concentrations in impacted houses were due primarily to short (less than 1 micrometer) fibers. Bulk samples did not reveal likely materials within the impacted houses to account for these differences. Thus high levels of waterborne asbestos were apparently the source of increased concentrations of airborne asbestos within these houses.

Calculations of beam spread for 1-MeV electrons within photographic emulsions based on a simplified model of multiple scattering are used to predict the performance of emulsions as a function of the silver-halide content and thickness of the emulsion layer. Experimental results are given for the sensitivity, resolution, figure of merit, and sensitivity per unit emulsion thickness for a range of photographic films exposed to 1-MeV electrons. Multiple scattering of 1-MeV electrons proves not to be the limiting factor that governs the resolution in the tested commercial films having conventional emulsion thicknesses and silver-halide contents. A new film design is proposed in order to mitigate the serious problem of the low sensitivity of the existing photographic films to 1-MeV electrons, which entails inordinate radiation damage to biological specimens during high-voltage micrography. This film would have an enhanced silver-halide content (as much as 65% AgBr by volume) and an increased emulsion thickness (up to 55 μm). As compared with a parent film having an emulsion 20% AgBr by volume and 25 μm thick, the proposed film should provide sensitivity enhanced sevenfold, with only about 17% loss in resolution. The new film should also show improved performance at conventional accelerating voltages (40–100 kV). Especial advantages are expected both in studying intrinsically radiation-sensitive objects and in studying those that require multiple exposures to the same specimen area, as in tilt series or time-lapse series.

The hyperglycemic pancreatic hormone, glucagon, may be crystallized in cubic crystals showing the form {110}, and having the space group P 2 1 3, with a = 47·94 A. There are 12 molecules of molecular weight 3,482 in the unit cell. A weight loss of 41 ± 2·5% on drying shows a degree of hydration typical of protein crystals. The crystals could be grown from phosphate buffers, as well as from glycine buffers, as has been reported in the literature. The space group requires that the molecules be grouped in triads about the three-fold axes. With this principle, and with the assumption that the molecules form unbroken α-helices under the conditions existing in the crystal (as permitted by the amino-acid sequence), a speculative structural model is developed.

Detailed methods are described for preparation of bovine pancreatic ribonuclease (polyribonucleotide 2-oligonucleotidotransferase (cyclizing), EC 2.7.7.16) crystals of Modifications I and II of quality suitable for X-ray diffraction studies. The reasons for choice of solvent and buffers systems are discussed, especial regard being paid to the use of the solvent 2-methyl-2,4-pentanediol and to the application of preserving solutions as media for handling the crystals after growth. Some necessary precautions are specified.

Light meromyosin-C, a fragment from the tail region of myosin prepared by cyanogen bromide cleavage, yields, under suitable conditions, an aggregate having the form of hollow tubes. Both the inclined striation patterns of these tubes and the existence of oblique paths of easy cleavage indicate that the molecules of light meromyosin-C follow helical arcs in these aggregates. From specimen to specimen, the molecular arcs vary widely in their inclination to the tube axes. Thus, they vary also in their radii of torsion and curvature. These data indicate not only that the tail of the myosin molecule is flexible, but also that its equilibrium configuration under certain conditions is non-linear, a situation of some importance in devising models for the thick filament.

Cyanogen bromide selectively cleaves the rod section of the myosin molecule at two specific methionyl residues lying approximately 950 A from the C-terminus. As a consequence, a large segment of the α-helical coiled-coil backbone of myosin (light meromyosin-C) is released fully intact without internal peptide bond interruptions. Since this molecule (unlike light meromyosin produced by tryptic cleavage) is a chemically homogeneous fragment of myosin, its aggregation properties have been examined with the electron microscope over a wide range of solvent conditions in an attempt to prepare true three-dimensional crystals. At least four ordered phases of light meromyosin-C aggregates have been identified. These phases are: (a) unbanded filaments; (b) paracrystalline tactoida which show a 143 A period when stained; (c) paracrystalline square nets with a 685 A repeat distance; (4) true crystals, based upon a stacking of layers of parallel strands running alternately in two mutually perpendicular directions. These reticulated crystals appear in projection as square nets with a repeat distance of 390 ± 10 A, and a plausible model has been built to account for their electron microscopic features.

Publisher Summary This chapter describes the definition and scope of mock stereo. A mock-stereo display is one that generates depth perception from parallax information arising from sources other than a shift of vantage point. Such displays have at times proved effective in various fields of study including electron microscopy and therefore it is interesting to examine the conditions under which such displays can prove advantageous. Mock-stereo displays can include before-and-after pictures of a scene in which some details have become shifted by motion or distortion of objects and comparisons to establish identity or equivalence of objects in two scenes. A criterion for selecting types of images as candidates for mock-stereo treatment is that this method should offer advantages over other modes of display in enhancing recognizability of features. Mock-stereo methods gain another advantage when one wishes to display two different types of disparities in an image pair simultaneously to the observer. One of the types can be assigned to the mock-stereo channel by displaying it as horizontal parallax, and the other.

In an experiment to evaluate the merit of isopycnic centrifugation as a method of separating cell types in human head and neck squamous cell carcinomas, cells have been isolated from four specimens of these tumors and subjected to isopycnic centrifugation in continuous Percoll gradients. Cell types were identified by electron microscopy. The R- (ribosome-rich), T- (tonofilament-rich), and RT- (intermediate) cell types yielded broad bands overlapping extensively with one another, and partially with the bands of leukocytes. The pattern differed for each tumor studied, so that universal density levels separating given cell types could not be found. Isopycnic centrifugation proves less suitable in analyzing cells dispersed from solid tumors than for cells in suspended culture, blood, effusions, etc., probably because of heterogeneous growth conditions of cells in solid tumors.

Publisher Summary This chapter discusses the theory and mechanisms of stereopsis. The view of the stereoptic mechanism that has emerged is one of a cerebral system for analyzing spatial information by integrating a wide variety of both binocular and monocular cues existing in the images seen by the two eyes. Its most potent source of depth cues is the disparity of positions of details in the two images, although many other features such as perspective and motion of objects in the scene also contribute greatly. The role of left-right positional disparities will be central to much of discussion, both because of the intrinsically large part they play in stereopsis and because they constitute the only type of depth information present in many electron microscopic situations, especially in the viewing of micrographs of tissue sections taken in the transmission electron microscope. The limiting angular disparities for breakaway and refusion prove to depend critically on the character of the object being examined and on their direction relative to the vector joining the observer's eyes, which is as the horizontal axis.

Various crystalline forms of bovine pancreatic ribonuclease, heated in their mother liquors, melt to form gels at temperatures characteristic of the crystal forms used. On incubation at 25° C, crystals grow again in the samples, usually of the same form as had originally been melted. Indications were obtained of a type of heterogeneity other than that previously reported in the literature for this protein.

PREVIOUS investigations1,2 of the various crystalline modifications of bovine pancreatic ribonuclease (hereinafter abbreviated as RNase) have shown that the growth of several of these depends on the presence of a metal compound in the crystallization medium. To be reported here are some observations throwing light on the structural role of the metal atoms in one of these modifications, namely, RNase I (space group P212121).

Summary Ribonuclease A (polyribonucleotide 2-oligonucleotidotransferase (cyclizing), EC 2.7.7.16) crystals were chemically modified by reaction with 1,5-difluoro-2,4-dinitrobenzene, which was permitted to diffuse into the crystals. Examination of modified crystals by X-ray diffraction revealed slightly altered lattice parameters and a substantially altered distribution of diffraction intensities as compared with the unmodified crystals, suggesting displacements of the molecules without loss of crystalline order. One monomer and two dimer fractions were isolated in a total of 20% yield from the reacted ribonuclease crystals by Sephadex G-75 gel nitration followed by IRC-50 chromatography. The remainder of the preparation was highly modified insoluble product (40%) and unmodified ribonuclease (33%). The monomeric ribonuclease derivative, while inactive toward cytidine 2′,3′-phosphate, had 2% of the ribonuclease A activity toward yeast RNA. The dimeric ribonuclease derivatives were inactive toward both substrates.

Eine Methode wird entwickelt, welche die Berechnung der Absorptionskorrekturen bei Messungen von Rontgendiffraktionsintensitaten von Kristallen beliebiger Form moglich macht. Dabei wird der Strahlengang auf einer elektronischen Rechenanlage simuliert, in der das Kristallabbild als Binarmuster gespeichert ist.

Both myosin and light meromyosin-C, a fragment prepared by cyanogen bromide cleavage, yield, under suitable solvent conditions, a variety of aggregates that have the form of side-by-side linear arrays. These resemble the segment structures obtained from myosin rods and light meromyosin derived from tryptic digestion (Cohen, Lowey, Harrison, Kendrick-Jones & Szent-Gyorgyi, 1970) and show that alternating antiparallel lateral packing is a common mode of aggregation among molecules containing the tail region of myosin. The aggregates exhibit a variety of overlap distances in response to changes in conditions and show that several patterns of molecular contacts are nearly equivalent energetically. Light meromyosin prepared by cyanogen bromide cleavage yields three segment phases which, when measured, give a molecular length of about 1025 A. These phases differ in overlap length and striation pattern. One of them is a helically twisted ribbon-like structure, and another may be a bilayer. Myosin yields aligned segments , in which the molecular tails are in exact register only at high concentrations of alkaline-earth metals. These structures give a length of 1654 ± 58 A for the myosin molecule. At lower concentrations of calcium or magnesium ions, myosin forms disordered segments and crossed segments in which overcrowding of the myosin heads is partially relieved by a random stagger in alignment of the tails. This process is facilitated by the ease with which myosin adopts alternative packing arrangements, and it throws some light on the morphogenesis of the thick filament of muscle.