Cross Fractures Research Articles

Spherulites, quench fractures and relict perlite in a Late Devonian rhyolite dyke, Queensland, Australia

A Late Devonian rhyolite dyke displays perlitic and other fracture sets, as well as textures generated by crystallisation of the glass. The dyke is less than a metre wide and has sharp contacts with ignimbrite. Although originally glassy, no glass is preserved. Aligned magnetite (after pyroxene?) microlites and trains of small (0.5–1 mm) spherical spherulites crystallised early, at temperatures above the glass transition temperature and before formation of the fracture sets. Long, subplanar fractures oriented perpendicular to the dyke walls extend almost the full dyke width and end by merging with adjacent long fractures. Short, subplanar cross fractures are perpendicular to and terminate at the long fractures. Well-defined perlitic fractures are present within the volumes of rock, generally < 10 × 5 × 5 mm, defined by the long and cross fractures. The geometry of the fracture sets suggests that the long fractures formed first, followed by the cross fractures and finally the perlitic fractures. The long and cross fractures are interpreted to be first- and second-order quench fractures, respectively. The perlitic fractures formed in the closely fractured glass, probably in response to strain inherited from rapid cooling contraction and volume changes associated with low-temperature hydration. Formerly glassy domains now consist of K-feldspar crystals radiating outward from the fractures (similar to axiolitic spherulites) and enclosing areas of polygonal quartz and oligoclase. This assemblage is the result of devitrification of the perlitised glass after initial cooling, most likely promoted by hydration, interaction with groundwater and elevated temperature. Fractures have been accentuated by concentrations of iron oxide deposited during surface weathering.

Alveolar lining layer is thin and continuous: low-temperature scanning electron microscopy of rat lung.

The low-temperature electron microscope, which preserves aqueous structures as solid water at liquid nitrogen temperature, was used to image the alveolar lining layer, including surfactant and its aqueous subphase, of air-filled lungs frozen in anesthetized rats at 15-cmH2O transpulmonary pressure. Lining layer thickness was measured on cross fractures of walls of the outermost subpleural alveoli that could be solidified with metal mirror cryofixation at rates sufficient to limit ice crystal growth to 10 nm and prevent appreciable water movement. The thickness of the liquid layer averaged 0.14 micron over relatively flat portions of the alveolar walls, 0.89 micron at the alveolar wall junctions, and 0.09 micron over the protruding features (9 rats, 20 walls, 16 junctions, and 146 areas), for an area-weighted average thickness of 0.2 micron. The alveolar lining layer appears continuous, submerging epithelial cell microvilli and intercellular junctional ridges; varies from a few nanometers to several micrometers in thickness, and serves to smooth the alveolar air-liquid interface in lungs inflated to zone 1 or 2 conditions.

Mathematical model of methane transport in coal seam

Cannel coals are tough, massive coals with a dull luster that break with an even, compact grain and conchoidal cross fractures. Historically, cannel coals were of significant economic and social importance during the early industrialization of the USA. They were the source for a sophisticated petrochemical industry and a fuel source for heating, gas making, coke making and oil generation. Petrographic data, proximate analysis and ultimate analysis data were obtained for 68 cannel coals from Kentucky to decide how well the cannel coals fit the generally-accepted definitions of a cannel coal. Four maceral assemblages were found—sporinite with abundant medium-grained vitrinite and inertinite, sporinite with abundant fine-grained vitrinite and inertinite of which micrinite is abundant (bituminite may be present), alginite with abundant fine-grained vitrinite and inertinite, and alginite and bituminite with minor vitrinite and inertinite. Volatile matter and H/C ratios are highest for those samples with abundant liptinite with a sample from Breckenridge having the highest value of each. Five samples were analyzed by the Rock-Eval method. The S2 and HI indices show that the coals would make excellent source rocks. Discrepancies between the values for the five samples are related to maceral composition and there may be a good correlation between source rock potential and importance as a feedstock for synthetic crude oil production in the 1800s. The maceral composition of the microlithotypes is related to the environment of deposition. Coal composed of assemblage (i) formed in humic peat swamps in which unusually large numbers of spores were introduced, possibly because of unusual, climatically controlled reproductive cycles. Coals composed of assemblages (ii) to (iv) formed as sapropelic coals in lakes at some stage of peat swamp development.

Buckling deformation in the Highwood Pass, Alberta, Canada

Buckling of beds in the sedimentary rocks in the Highwood Pass, Alberta, Canada, occurs on steep underdip and dip slopes. The modes of buckling are determined by bedding thickness. We distinguish Euler buckles that develop in beds without cross fractures, block-flexure buckles that form with smooth buckled bedding surfaces in beds with cross fractures, and block buckles that develop with large rotations of rock blocks in rock layers more than 0.1 m thick. Chevron buckles resembling chevron folds develop in beds less than 0.1 m thick. Buckles can be displaced further to form roof and wall structures or cascades. Key words : buckling, critical load, slope stability, natural rock slope.

An Optimized Freeze-Fracture Replication Procedure for Human Skin

This in vitro study aimed at substantial modification of the freeze-fracture replication technique (FFRT) which should result in an optimal visualization of the ultrastructure of human skin. The technique was modified in two ways: firstly, the conventional sample holders such as gold cups and copper plates were replaced by silver cylinders (83.5% silver, 16.5% copper) resulting in almost perpendicular cross fractures through the skin. Secondly, the replica cleaning procedure was optimized through the following sequence of treatments. Firstly, a mild tissue destruction was obtained by simultaneous lipid solvation and water extraction with absolute methanol (20 h), followed by protein denaturation with dimethyl sulfoxide (DMSO, 24 h). Subsequently, a final treatment was given using an alkaline sodium hypochlorite solution (20% KOH/13% NaClO; 1:3 v/v, 4 d). After rinsing the replicas for 45 min in aqua bidest, they were mounted on copper grids and examined in the transmission electron microscope (TEM). The combination of the unorthodox fracturing method and the optimized cleaning procedure yielded large, practically undamaged and very clean replicas of near perpendicular cross fractures through human skin. Common handicaps related to current freeze-fracture procedures when applied to skin, such as incomplete cleaning and fragmentation of replicas and oblique or irregular fracturing planes, can largely be avoided in this way. In this paper a complete description of the method is given, and a number of advantages are illustrated with the aid of TEM micrographs.

Batopilas mining district, Chihuahua

The Batopilas mining district is one of the few mining districts where the major ore mineral is native silver. The native silver occurs as fissure vein deposits in granodiorite, fine-grained diorite, and dacite. Orebodies are irregularly shaped pods of massive native silver in calcite and may contain up to 75 wt percent silver. The veins formed along north- and northeast-trending fractures and faults.The geologic history of the district is summarized as follows: intrusion of the Pastrana dacite, Dolores microquartz diorite, and Tahonas granodiorite, sequentially, into preexisting Mesozoic sediments and/or igneous rocks. Some of these intrusive events may have vented to the surface. After the intrusions were eroded, the San Jose, Arenal, and Casas Coloradas flow breccias were deposited. Between each episode of flow breccia deposition, there occurred periods of tectonism and erosion. After a fourth major episode of tectonism and erosion, the massive ignimbrites of the upper volcanic series represented by the Yerbanis Formation were deposited. Contemporaneous with Yerbanis deposition was the intrusion of rhyolite dikes. Numerous andesitc dikes of uncertain age are also present.The native silver orebodies are generally less than 30 m in length with the width varying from a few centimeters to 4.6 m and averaging 0.8 m. The ore-grade mineralization terminates abruptly in both vertical and horizontal directions. The orebodies are connected vertically and along strike by up to 90 m of unmineralized fractures or vein stringers of calcite, sometimes less than 3 mm wide.Flexures in vein orientation and/or cross fractures are associated with some orebodies, whereas other orebodies have no apparent structural control. Most orebodies are hosted by Pastrana dacite and Tahonas granodiorite.Three types of wall-rock alteration are found with the silver mineralization: (1) chlorite-actinolite alteration, (2) silicification, and (3) pyritization. Chlorite-actinolite alteration is often associated with gray and green argillization. The host rocks of many, but not all, orebodies have experienced chlorite-actinolite alteration and pyritization. Silicification occurs in dikelike masses within the Dolores and Pastrana units. These silicified zones are generally less than 9 m wide. Pyritization is found in the intrusions. Minor quartz-pyrite veins are found throughout.Gangue in the Batopiias ores is calcite and is associated with small amounts of sphalerite, galena, and laumontite. Cobalt-nickel arsenides and ruby silvers have been reported, but their presence is not confirmed by this investigation. Pyrite is abundant in the host rocks but is absent from the ores.Two kilometers southwest of the village of Batopilas is an area of approximately 5 km 2 devoid of vegetation, the hillsides and tops have a thick gossan (Corralitos). The underlying Tahonas granodiorite exhibits widespread sericitic alteration, and extensive to almost complete quartz veining and replacement are present. Chalcanthite stalagtites form on many overhangs along the arroyos. This area is interpreted as the Tahonas porphyry copper deposit.A well-developed pattern of mineralogic zonation exists in the district. This zonation is concentric around the Tahonas porphyry copper deposit. Preliminary fluid inclusion studies document homogenization temperatures (T h ) between 217 degrees and 434 degrees C, and salinities over 20 equiv wt percent NaCl for quartz from the Tahonas porphyry copper deposit. Studies on quartz from outlying regions give homogenization temperature ranges of 224 degrees to 351 degrees C, and salinities of from 9 to 18 equiv wt percent NaCl. Studies of the later generation of calcite, silver, and minor sulfides give (T h ) values between 137 degrees and 257 degrees C for calcite and 170 degrees to 196 degrees C for sphalerite. Salinities in calcite are concentrated between 7.6 and 13.2 equiv wt percent NaCl. The estimated 300 million oz (9.3 million kg) of silver produced to date probably was deposited from circulating connate waters adjacent to the Tahonas porphyry copper mineralizing system.

Visualization of contact sites between outer and inner envelope membranes in isolated chloroplasts

Contact sites between outer and inner envelope membranes of isolated chloroplasts have been studied at the ultrastructural level by two different electron microscopical methods, i.e., freeze fracturing and freeze substitution followed by ultrathin sectioning. Both methods demonstrate that approx. 10% of the chloroplast population exhibits blister-like structures. Cross fractures and ultrathin sections of freeze-substituted chloroplasts reveal that the blisters originated from a separation of the outer and inner envelope membranes. Exposure of isolated chloroplasts to hypertonic conditions results in an almost complete separation of the two envelope membranes, except for small regions in which the two membranes are in close contact. These contact sites are clearly recognized in freeze-fracture replicas by ridges of a high density of intramembrane particles. In addition, cross fractures and thin sections of freeze-substituted chloroplasts demonstrate the presence of small vesicles associated with the outer envelope membrane. As indicated by the opacity of the vesicle and demonstrated by immuno-gold labeling, these vesicles, which originate from the inner envelope membrane, contain stroma-derived proteins.

Diagenesis and Structural Control on Production from Devonian Duperow Formation, Tree Top Field, Billings Anticline, North Dakota: ABSTRACT

The Billings anticline is a north-plunging structure in the Williston basin of west-central North Dakota that is covered by most of the Phanerozoic section. Structure and isopach maps of the Duperow Formation suggest that the structure is fault bounded on the east side and apparently crossed by a series of northeast-southwest-trending fractures. Tree Top field is located on the eastern side of the structure. Hydrocarbons are produced from rocks of three different ages in more than four zones, including the Duperow Formation. Tree Top field is one of six fields on the anticline producing from the Duperow Formation. Tree Top field has produced over 350,000 bbl of Duperow oil since its discovery in 1979. Essentially, one well has produced 84% of this oil. The well is located proximal to the junction of the east-bounding fault and one of the apparent cross fractures. Maps of porosity and lithology of the producing zone show lateral porosity pinch-out coincident with lithologic changes from dolomite to limestone. The Duperow Formation consists of numerous complete and incomplete, shallow-water deposition, sediment packages. The producing zone in Tree Top field is in the heavily dolomitized subbank and perilittoral zones of cycle 3. Core analyses show that themore » dominant type of porosity in the dolomite is intercrystalline and is enhanced by molds and microvugs. Intercrystalline porosity is being altered by replacement and infilling by anhydrite and calcite. Core analyses, in conjunction with lithologic, porosity, structure, and isopach maps of the pay zone, suggest that the preservation and enhancement of dolomite porosity may be most effective proximal to fracture zones.« less

リオープン, シャットインおよび水循環によるき裂挙動

The purpose of this report is to discuss how to account for the fracture behaviors in re-opening, shut-in and circulation. Some laboratory re-opening and shut-in tests were conducted under various stress condition, and circulation tests were conducted under various flow rate and stress condition for single and cross hydro-fractures created in Inada granite and Kofu andesite.The results of re-opening tests show that the values of re-opening pressure are of high application to stress evaluation because of the smaller influences of flow rate and permeation. The values of shut-in pressure were recognized to be equal to the normal stresses to fracture with 20% of accuracy for created fractures in 30 cm cubical specimens.The relationship between steady flow pressure and square root of injected flow rate was obtained to be linear by circulation tests for single fracture, and for cross fractures, steady flow pressure were recognized to be limited in spite of increasing of injected flow rate. It is suggested from the comparison of the results of circulation tests and numerical analyses through coupled F. E. M. and D. D. M. on finite element that the existences of the residual aperture of fracture under stressed condition which comes from asperities of the fracture must be taken into consideration in the model for more precise simulation.

Freeze-fracture confirmation of the presence of a core in the specialized tip structure of Mycoplasma pneumoniae.

The presence of a specialized terminal region in Mycoplasma pneumoniae was seen in thin sections viewed in an electron microscope. Actively growing cells were examined by the freeze-fracture technique in the absence of fixation to further establish the core as a significant structural entity. Cross fractures revealed a cytoplasmic matrix surrounding a central core structure of about 54 nm. This structure disappeared rapidly in aging cells. The convex protoplastic faces of the membrane around the core had characteristic 5- to 10-nm intramembrane particles evenly distributed across the cell surface, with no apparent difference in the region of the specialized tip. A periodicity previously noted in negatively stained preparations was clearly defined here in thin sections. Attachment of actively growing cells to sheep erythrocytes was seen primarily as a side attachment rather than attachment at the tip alone. This association between the mycoplasma and the sheep erythrocytes seriously deformed the sheep erythrocytes, but no membrane fusion could be detected.

Nuclear and chromatin structure in rat spermatozoa

AbstractThe nuclei of mature mammalian spermatozoa contain a highly ordered, lamellar substructure, presumably constituting the nucleoprotein of the haploid chromosomal complement. With a view toward constructing a plausible model of chromatin packing in sperm, we have determined some of the quantitative parameters associated with these “nuclear lamellae” in rat spermatozoa. Epididymal sperm from white, Sprague‐Dawley rats were examined by conventional sectioning methods, freeze fracture of fixed and unfixed specimens, and by whole mount replica techniques. Fixation and glycerolation did not significantly alter nuclear structure as seen by freeze fracture. Numerical data obtained from cross fractures of sperm heads indicate that the number of lamellae are quite constant at 10.4 ± 1.8 and that the linear measure of the lamellae is 7.2 ± 2.3 μm per cross fracture. The total area of cross fracture, assuming an elliptical profile is 2.3 k 0.7 μm2 and the thickness of the lamellae is 18.2 ± 3.5 nm with a range of 13.5 to 25.5 nm. An estimate of the total surface area of the nuclear lamellae could be made from measurements of projected nuclear area (from replicas and sections) as 173 ± 15 μm2. From these data and the known amount of DNA in the rat sperm nucleus, a model can be proposed for the organization of the nucleoprotein in these lamellar sheets. It is suggested that the chromatin is arranged in a coiled‐coil configuration closely associated together in a side‐by‐side fashion and continuous in extent. Approximate calculations based on this simple model are within a factor of 2 or 3 of predicting the correct amount of DNA in the sperm nucleus.

Description of the mitochondria—axoneme junction in sea urchin spermatozoa: Presence of a flagellar necklace

Freeze—fracture electron microscopy has been used to investigate the morphology of the plasma membrane of the midpiece region in the Arbacia lixula sea urchin spermatozoon. The proximal part of the flagellum which is anchored in the nuclear depression is hidden in a cavity delimited by the mitochondrial ring. Longitudinal fractures of the plasma membrane never proceeded inside this cavity. However by distorting the mitochondrial ring, it was possible to unfold and expose to the fracture the plasmic membrane thus showing the existence of a flagellar necklace at the head—flagellar junction. Its actual location was determined on nondistorted sperm from observations of cross fractures of the midpiece revealing the very proximal part of the flagellum within the cavity. The three strands of particles of the flagellar neclace were located on the P face of the plasmic membrane covering the flagellum at less than 50 nm from its emergence from the nuclear depression.

Specialized intramembrane organizations of the cone presynaptic membrane in the pigeon retina. Freeze-fracture study.

The presynaptic membranes of the cone cell endings of the pigeon retina were investigated using the freeze-fracture technique. En face views of the cytoplasmic leaflet (P-face) of the split presynaptic membrane revealed several specialized membrane organizations, 1. membrane particle aggregates composed of 10-20 particles which were larger than the usual ones seen in the cell membrane, 2. fenestration-like circular structures of 30-50 nm in diameter which were not surrounded by membrane particles. 3. similiar circular structures as described above but which were accompanied by a few membrane particles on the circular margin and were considered to be an intermediate form of the first and second membrane structures. These three structures appeared simultaneously in one fracture plane of the presynaptic membrane; were situated at the same intervals from one another and were approximately equal in size to synaptic vesicles (30-50 nm). These findings strongly suggested that these three structures were serial events in presynaptic membrane organization. When fortuitous cross fractures exposed both the P-face of the presynaptic membrane and the adjacent cytoplasm of the cone ending, fusion of the synaptic vesicles to the presynaptic membrane was observed, and was considered to be the opening of the synaptic vesicle to the synaptic cleft. These openings were also situated at the same distance as the structures described above. These findings demonstrate the process of exocytosis of the synaptic vesicles by which the chemical transmitter is probably released to the synaptic cleft.

The structure of the surface membranes in rat heart muscle mitochondria as revealed by freeze-fracturing

The two surface membranes of rat heart muscle mitochondria are structurally very different. They both also differ structurally from the crista membranes. There is therefore no justification to consider the crista membranes as mere infoldings of the innermost surface membrane. Most of the earlier freeze-fracture studies on intact mitochondria have predominantly involved the innermost surface membrane. The conclusions drawn from these studies therefore cannot be accepted as being relevant to the crista membranes. Of the two surface membranes, the outermost showed the simplest structure. Fish scale-like particles measuring 120 to 240 A in width and a second type of particle measuring 120 A in diameter were distributed over an otherwise mostly smooth surface. The former particles extended through the entire membrane. The innermost surface membrane consisted of closely aggregated particles in a monolayer. Irregularities in the inner surface of this membrane could be related to stalk-like connections extending from this membrane to the inner membranes of the cristae. The thickness of the innermost surface membrane was measured on cross fractures to be 70 A. The distribution of the dimensions of the particles of this membrane deviated from that of the inner membranes. Particles with diameters measuring 100 to 150 A in directions parallel to the plane of the membrane thus dominated in the innermost surface membrane. The distinguishing of three structurally different types of membranes in heart muscle mitochondria agrees with the observations made by Sjostrand (1977, J. Ultrastruct. Res. 59, 292–319) on material that had been prepared according to the low denaturation techniques. The thicknesses of the surface membranes measured on the freeze-fractured material also agree with those determined on material prepared according to the low denaturation techniques.

Similarity of junctions between plasma membranes and endoplasmic reticulum in muscle and neurons.

The structure of membranes at junctions between the plasma membrane and underlying cisterns of endoplasmic reticulum in amphioxus muscle and mouse cerebellar neurons was studied using the freeze-fracture technique. In amphioxus muscle, subsurface cisterns of sarcoplasmic reticulum form junctions with the surface membrane at the level of the sarcomere I bands. On the protoplasmic leaflet of the sarcolemma overlying these junctions were aggregates of large particles. On the protoplasmic leaflet of the membranes of cerebellar basket, stellate and Purkinie cells there were similar aggregates of large particles. In both tissues, the corresponding external membrane halves had arrays of pits apparently complementary to the aggregates of large particles. Cross fractures through junctions showed that the particle aggregates in neuronal and muscle membranes were consistently located over intracellular cisterns closely applied to the plasma membrane. Thus, a similar plasma membrane specialization is found at subsurface cisterns in mammalian neurons and amphioxus muscle. This similarity supports the hypothesis that subsurface cisterns in neurons, like those in muscle, couple some intracellular activity to the electrical activity of the plasma membrane.

Freeze-etch and histochemical evidence for cycling in crayfish photoreceptor membranes.

Freeze-etched rhabdoms and adjacent cytoplasmic cytoplasmic organelles from crayfish compound eyes have been studied for evidence of photoreceptor membrane cycling. The protoplasmic leaflet face (PF) of split photoreceptor membrane of the microvilli is richly particulate. The particles (92 +/- 16 A in diameter in surface fractures; 70 +/- 9 A in cross fractures; density about 8000/mum2) probably indicate rhodopsin molecule localization. Closely similar particles appear in membranes of pinocytotic vesicles, multivesicular bodies (MVB) and secondary lysosomes. In contrast other retinular cell membranes like plasma membrane remote from the rhabdom are quite distinct (60 +/- 23 A particle diameter, density ca 1000/mum2.) Histochemical tests for acid phosphatase demonstrate its presence in well-developed (but not early stage) MVBs, mixed lamellar vesicular bodies (LVB) and lamellar bodies. Density of PF particles decreases from 8000 in MVB to roughly 4500/mum2 in LVB indicating a degradative sequence from rhabdom to lamellar bodies. Membrane leaflet orientations show that primary endocytosis from microvilli must be followed by secondary endocytosis of fused coated vesicles to form MVB. Morphological evidence for photoreceptor membrane resynthesis has not been found yet in crayfish but some has been obtained in other crustaceans.

Trans-glial channels in ventral nerve roots of crayfish.

The sheath around the roots of the sixth abdominal ganglion in the ventral nerve cord of the crayfish consists of concentric layers of thin glial processes alternating with wide clefts containing filamentous connective tissue. Regions of each glial lamella are perforated by single, short, tubular channels: the trans-glial channels. In thin plastic sections examined in the electron microscope, the channels appear as slits that are 240 A wide and 450-550 A long which traverse glial lamellae less than 1,500 A thick. Branched tubular channels cross glial sheets that are thicker than 1,500 A. The thickest glial wrap is adaxonal; it closely encapsulates individual axons and its cell membrane is separated from the axolemma by a collagen-free space of only 150 A. The adaxonal glial cytoplasm contains unique, three-dimensional networks of interconnected tubules. Separate tubular lattices occur along these thicker processes. In replicas of freeze-fractured sheaths, the outer half of the plasma membrane belonging to the thin glial sheets exhibits many volcano-like protrusions which represent cross fractures through the necks of trans-glial channels. Corresponding depressions on the inner half of these membranes are sites where the plasma membrane invaginates to form the channels. Although some channels are randomly dispersed, others are lineraly positioned in restricted areas across successive glial layers. The number of channels is far more readily appreciated in replicas than in thin sections. The average frequency of channels is 16 per mu2 (range 8 to 33) in normal roots and does not differ significantly from the average of 13 per mu2 in proximal stumps of roots fixed three to four weeks after the roots were cut. The channels are not precisely aligned from one glial layer to the next but do appear to coincide approximately with the adaxonal tubular lattice. The combination of trans-glial channels and adaxonal tubular lattices may provide a complex conduit that could facilitate a rapid, passive flow of electrolytes and nutrients across the nerve sheath to the axonal surface. Horseradish peroxidase solutions bathing the ventral roots enter the trans-glial channels, extracellular clefts and finally the tubular lattices. This distribution supports the proposed role of the channels in a rapid extracellular passage of solutes. The channel profiles have a range of forms consistent with the supposition that they are not static but continually reforming. There are indications that, proximal to the cut, the areas of glial plasma membrane with channel profiles contain more junctional complexes between regenerating cells than between glial cells of normal sheaths. The channel profiles and aggregates of particles belonging to junctions are closely associated when they occupy the same region of the membrane.

Fenestrae in golgi and endoplasmic reticulum cisternae of human brain tumours

Fenestrae were found in freeze-fractured cisternae of the Golgi apparatus and endoplasmic reticulum of glioblastoma, oligodendroglioma, ependymoma, medulloblastoma, medulloepithelioma, meningioma, cerebellar sarcoma, hemangioblastoma, and chromophobe adenoma. They were about 200--400 A in diameter and often diffusely distributed or concentrated in groups in Golgi cisternae, while they were around 300--600 A in size and scattered in distribution in cisternae of endoplasmic reticulum. They appeared as conical protrusions or circular broken-off necks of face A and as circular holes on face B in tangential fractures, and as several constrictions of cisternae in cross fractures.

Freeze-fracture of microtubules and bridges in motile axostyles.

A freeze-fracture study of the motile axostyles of the flagellate protozoa Saccinobaculus and Pyrsonympha has been undertaken in order to obtain a view of the relationships of microtubules and their cross bridges not dependent on conventional preparative procedures. Reactivation studies using isolated axostyles prepared for freeze-fracture and then thawed demonstrate that we are observing the structure of a potentially functional axostyle. Cross fractures through the axostyle demonstrate more extensive interrow bridging than expected on the basis of observations of thin-sectioned material. Each microtubule has approximately sixfold bridge-binding sites with connections to as many as four interrow bridges. Measurements of microtubule diameter and spacing are significantly larger than those made from sectioned material and may indicate that conventional processing for electron microscopy results in the loss of structurally important water within the microtubule in addition to loss of intertubule material. Longitudinal fractures through the axostyle at various orientations demonstrate a minimum longitudinal periodicity of 160 A for both the spacing of the globular subunits within the microtubule wall and the spacing of the intrarow bridges. While intrarow bridges are strictly periodic and always oriented in parallel, interrow bridges are not strictly periodic and can be oriented at varying angles to the microtubule axis.

The structure of cytochrome oxidase membranes

Two preparations of oxidized membranous cytochrome oxidase were examined using both the negative stain and freeze fracture techniques of electron microscopy. The cholate preparation, containing 27% phospholipid by weight, appeared as membrane sheets. With the freeze fracture technique, cross fractures of the sheets showed particles abutted one against another. The Triton preparation, containing 42% phospholipid by weight, was decidedly vesicular and only particulate membrane fracture surfaces were usually seen. In the case of membranous cytochrome oxidase it is proposed that fractures follow the surface rather than a centre plane through the hydrophobic interior of the membrane. The observed particles appeared as prolate spheroids of 135 A X 68 A with the long axis extended through the membrane. From the size shape relationships, a molecular weight of 244 000 was calculated which is in agreement with values reported for dispersed cytochrome oxidase using other physical techniques. At least 50% of the protein is exposed to the aqueous environment. Cytochrome oxidase is a lipoprotein that spontaneously forms membranes under conditions of low ionic strength and the absence of detergents. Sun et al. [ 1 ] showed that these membranes were trilaminate structures 55 A thick when examined by conventional thin section techniques. Negatively stained preparations showed a membrane surface covered with 50 A particles. Seki and Oda [2] have shown