摘要:

SUMMARYParamylon storage granules fromEuglena graciliswere characterized by electron diffraction techniques using electrons of various accelerating voltages: 2 MV for the thick granules and 100 kV for the thinner ones. Intact granules gave well resolved, characteristic (1→3)‐β‐dglucan fibre diffraction diagrams with the glucan molecular orientation parallel to the longer axis of the granule. Hydrated electron diffraction patterns with better resolution were obtained from thinner granules by examination at low temperatures of quench‐frozen specimens. In this case, the pattern indexed on an hexagonal system witha=b= 1·55 + 0·01 nm andc(fibre axis) = 1·86 ± 0·01 nm. Sections of embedded granules provided single crystal‐like electron diffraction patterns corresponding to various sections of the reciprocal lattice of (1→3)‐β‐dglucan (including the hko section). Finally, by scanning electron microscopy, it was shown that the granules swell on contact with water and take up a characteristic ribb

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01206.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYTwo devices for measuring the beam current in an electron microscope are described; a Faraday cage rod for accurate absolute measurements in the specimen position and a collector plate mounted in the viewing chamber, which may be used continuously during experiments, for relative current measurements. Results of experiments to determine the effect of secondary electrons on, and choice of material of, the collector plate are presented. An example of the use of the collector plate as a photometer is given.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01207.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYA cryofixation method is presented which gives excellent ultrastructural preservation of monolayer cell cultures without any chemical pretreatments. Rat hepatocytes in primary culture were used in this study. The equipment needed is inexpensive and easy to manufacture. Cells are grown on a usual tissue culture support material (Thermanox plastic sheets). For cryofixation, samples are prepared essentially by a combined sandwich‐cryogen‐jet technique. 3 mm large discs are punched out and sandwiched with Cu‐ or Au‐object holders of little mass; a 15 μm spacer is put in between. The viability of the cells is not impaired by the manipulations before freezing. The sandwich sample is quickly frozen by shooting a propane jet from a simple pressure chamber on to the metal object holder. The relevant parameters were optimized by parallel freeze‐fracture analyses of 5% glycerol as a model system and by thermocouple measurements. Sandwich samples are then mounted in an appropriate double replication specimen table for further analysis by freeze‐fracturing. It is possible to obtain a certain selectivity of the fracture plane with regard to apical, lateral or basal aspects of the cell layer. Alternatively, disc samples can be processed by chemical fixation methods (including freeze substitution to determine the freeze‐fracture plane), since the support material Thermanox is insensitive to organic solvents and easy to cut. In each case the cells remain attached to their substratum throughout the whole procedure. Thus, the ultrastructural data can be directly correlated with parallel functional analyses obtained from the same

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01208.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYThe replicas obtained from various microemulsions prepared under different freezing conditions were observed by electron microscopy. The difficulties encountered in obtaining proper freezing may be related to the peculiar properties of such systems. A proposal is made for using systems with particular physical characteristics, which preserve the micellar structure during freezing, instead of looking for perfect freezing conditions. This proposal proved to be successful.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01209.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYThe use of zinc uranyl acetate as a sodium precipitant was investigated during conventional fixation and freeze‐substitution preparations; it was superior to antimonate reagents insofar as it only precipitated Na+and K+(Ca2+and Mg2+were not detected) and could be used in conjunction with freeze‐substitution in acet

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01210.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYIn the course of preparing specimens for scanning electron microscopy, both glutaraldehyde and OsO4‐fixed cells exhibit a considerable shrinkage with a reduction of the mean cellular diameter of about 45% after critical point drying. However, if cells are successively treated with glutaraldehyde, OsO4, tannic acid and uranyl acetate solutions, cellular shrinkage of only 5% is observe

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01211.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYThin sections of unfixed kidney, fast frozen without cryoprotectants, were fixed in osmium tetroxide vapour directly after freeze drying or after 30 min in a moist atmosphere. Dry sections fixed in vapour showed ice crystal damage characteristic for the freezing procedure. This was demonstrated with freeze fracture replicas from the same preparation. Ice crystal holes were obscured in serial sections which were freeze dried and allowed to rehydrate in a moist atmosphere. The same ultrastructural appearance was observed in frozen sections brought to room temperature immediately after cutting. Frozen thin sections from unfixed tissue, if freeze dried, are very sensitive to atmospheric conditions and need some form of stabilization (e.g. osmium vapour fixation, sealing with an evaporated carbon film) before electron microscope images can be interpreted as representative for the frozen state. Restoration of ice crystal damage can occur by melting frozen sections or by rehydration of freeze dried frozen sections. Restoration phenomena will impair studies aimed at the localization of diffusible substances by autoradiography or X‐ray microanalysi

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01212.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYMicrocrystals ofB. subtilisα‐amylase have been negatively stained and examined by electron microscopy. The micrographs were then subjected to spatial filtering and averaging using a Fourier transform procedure programmed for a mini computer. From these ‘enhanced’ images refined crystallographic parameters were obtained and a model for the packing of the asymmetric units within the crystal was derived. In addition, these parameters obtained from electron microscopy are compared with those derived from limited X‐ray diffraction data on macrocrystals of the s

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01213.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYSilica microspheres bearing a known surface charge were used to test the adhesive properties of support films and support film treatments commonly used in the electron microscopy of particulate specimens. Adhesion was strongly correlated with surface charge, negatively charged microspheres binding well only to positively charged support films and vice versa in solutions of low ionic strength. This charge dependency could be overcome by increasing the ionic strength to about 100 mmol with monovalent cations; under these conditions, it was not necessary to provide an oppositely charged film surface to obtain adhesion. Chromatin particles (nucleosomes) which have a net negative charge, behaved very much like the negatively charged silica with respect to adhesion, confirming that the microspheres provided an accurate indication of support film surface properties. The chromatin particles showed dramatic structural changes under conditions when adhesion was either poor, or very strong, indicating the need for careful selection of binding conditions for delicate biological specimens. A new and simple method for pretreating carbon films to improve adhesion was developed, and a preliminary account of this technique is presented.

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01214.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY

摘要:

SUMMARYFor accurate photometric measurements linearity between the measured property of the object, e.g. transmittance, reflectance, fluorescence intensity, and the measuring signal plays an important role. Although modern photoelectric equipment is designed to provide practically perfect linearity there may be factors by which linearity is disturbed, e.g. ageing, heating, improper operation of equipment, defects in electric circuits, etc. The three‐polar method described in this paper involves the most convenient and objective testing of linearity by the operato

ISSN:0022-2720    

DOI:10.1111/j.1365-2818.1981.tb01215.x

出版商:Blackwell Publishing Ltd    

年代:1981

数据来源: WILEY