摘要:

Purple membranes were imaged dry and in water with the atomic force microscope. Slowly air‐dried purple membranes showed large cracks on one side and narrow cracks on the other side. Purple membranes that were imaged in water adsorbed to mica showed no cracks. The hexagonal arrangement of the bacteriorhodopsin molecules could be seen in the two‐dimensional Fourier transform from images obtained in water. Often spots to the fifth order corresponding to about 1.1 nm resolution were observed.

ISSN:0734-211X    

DOI:10.1116/1.585245

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A scanning tunneling microscopy (STM) study of the lipoprotein ice nucleator (LPIN) from hemolymph of the cranefly,Tipulatrivittata, showed strong organization of the individual LPINs into chain structures. Each strand of the chain is two lipoproteins wide with the lipoproteins arranged in aligned conformation. The size of the spherical LPINs within the strands (diameter of 90–120 Å) agrees with the value of 135±29 Å obtained from transmission electron microscopy (TEM). A non‐ice‐nucleating lipoprotein fromManducasextawas used as a control. TheManducalipoprotein does not exhibit any organizational tendency, but sometimes forms large aggregates. The two apolipoproteins of the LPIN, Apo‐I (MW=265 000) and Apo‐II (MW=82 000) were also imaged. The apolipoproteins exist as isolated individuals with platelike morphology, indicating the possibility of protein unfolding.

ISSN:0734-211X    

DOI:10.1116/1.585246

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) images have been obtained for three different types of uncoated helical flagella of bacteria, salmonella typhimurium SJW1103: intact flagella, sonicated flagella, and disassembled flagella (i.e., flagellin). Glycerol has been added to the desalinated sample solutions to prevent the aggregation of the sample in the solution, and to adhere to the samples onto the graphite surface. Freeze drying has been used to prevent the aggregation of the sample in the drying process. The molecular arrangement observed by STM is similar to that of the reported structure for straight flagella determined by x‐ray diffraction.

ISSN:0734-211X    

DOI:10.1116/1.585247

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy has been used to obtain images in constant current mode in air at molecular resolution of the polysaccharides: cellulose azure, hydroxypropylcellulose (hpc), and xanthan. The molecules were deposited from solution onto a graphite substrate. The hpc samples were observed to form readily ordered molecular arrays on the substrate. The molecular dimensions of width and repeat distance along the molecule were found to be close to values previously determined by x‐ray diffraction. The observed axial periodicity of 2 nm for xanthan is close to that expected for a double‐helix molecule.

ISSN:0734-211X    

DOI:10.1116/1.585248

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have developed an underwater atomic force microscope (AFM) based on detection by tunneling for investigations of single living cells. The AFM setup allows compensation of the electrochemical potentials involved and is integrated into a high magnification optical microscope. Small living cells are sucked onto a microcapillary and are brought into contact with a cantilever for imaging. The cells are kept alive under appropriate physiological conditions while maintaining high resolution to image their molecular structures. For the first time, images of red blood cells made under these conditions with resolution down to about 10 nm are shown. In addition, changes induced by higher salt concentration and by the sticking of antibodies to the cell surface were observed. This indicates the wide range of possibilities of this method for studying dynamical processes of living organismsinsituwith high spatial resolution.

ISSN:0734-211X    

DOI:10.1116/1.585206

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We demonstrate that a scanning tunneling microscope can be used to obtain structural information on membrane proteins in their natural environment and of isolated protein molecules deposited on graphite. We focused on ion channel forming proteins, i.e., gramicidin and the nicotinic acetylcholine receptor. The latter is a well described membrane channel in the neuromuscular synapse. To get more than topological information we developed a fast and stable method to characterize the changes of the current/voltage curvature while scanning over a sample. This results in a material‐dependent image color which is also sensitive to variations of chemical structure inside the molecule. The method was first tested with liquid crystals on graphite clearly showing their atomic structure in the STM image. In a second step the method was applied to obtain structural information about gramicidin adsorbed on graphite.

ISSN:0734-211X    

DOI:10.1116/1.585207

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Two globular proteins, lysozyme and chymotrypsinogen A, were imaged on graphite using a scanning tunneling microscope. In contrast to the isolated molecules typically seen, long‐range order was observed in both of these systems when the protein concentration of the solution deposited on the graphite was sufficient for multilayer coverage. For lysozyme, regular two‐dimensional arrays of protein molecules were seen, with periodicities ranging from about 40 (the approximate size of a lysozyme molecule) to about 150 Å. These length scales depend on the lysozyme concentration in the initial solution. For chymotrypsinogen A, two‐dimensional structures that covered a much smaller area of the graphite were observed. The structural features observed suggest such possibilities as protein structure determination using surface structural techniques and epitaxial growth of protein crystals on these two‐dimensional structures.

ISSN:0734-211X    

DOI:10.1116/1.585208

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) is used to image fine surface detail of cytokeratin α‐helical protein. Resolution of molecular structure increased with extended exposure of partially purified cytokeratin protein to cold temperatures from 12 to 48 h. Surface of a cytokeratin tetrameric units resolved by STM depicts 2 nm diam wraps of cytokeratin proteins.

ISSN:0734-211X    

DOI:10.1116/1.585209

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy images of uncoated purple membrane are easily obtained at tunneling currents lower than 1 pA and tunneling voltages above ∼7 V. However, the images sometimes show positive, sometimes negative contrast. This effect appears to depend only on the shape of the tunneling tip. A simple model, assuming a constant voltage drop across the purple membrane, is proposed which can explain this observation.

ISSN:0734-211X    

DOI:10.1116/1.585210

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We propose a general model for the interaction between a scanning tunneling microscope tip and a surface being imaged in air. The van der Waals force and a liquid bridge formed from condensation cause a net attraction between the tip and sample. If the sample is flexible or weakly bound to the scanning tunneling microscopy (STM) base our model predicts this attraction can lead to a significant amplification of the height of surface features. STM images of a freeze‐fracture replica of a mica surface clearly show the amplification. Freshly made replicas of an atomically smooth mica surface had a standard deviation in their heights of 0.51 nm, but this increased to 0.61 nm after five days in a Petri dish and to 1.64 nm after one day of exposure to air. Methods of further reducing the amplification are discussed.

ISSN:0734-211X    

DOI:10.1116/1.585211

出版商:American Vacuum Society    

年代:1991

数据来源: AIP