摘要:

Enzymes can be immobilized at a solid–liquid interface and observed with a scanning tunneling microscope (STM) using the inherent charge of proteins and an external potential applied to the STM substrate. Phosphorylase kinase, and dimers and oligomers of phosphorylasebhave been observed at the interface of aqueous solutions and highly oriented pyrolytic graphite (HOPG). The lateral dimensions of phosphorylase kinase determined by STM at the solid–liquid interface are from 74%–78% of the dimensions determined by STM at the solid–air interface [Biochem.28, 4939 (1989); Biophys. J. (in press)]. The phosphorylaseblateral dimensions of both enzymes are between 1.9 and 2.5 nm greater than the dimensions determined by x‐ray crystallography. The vertical dimensions determined by STM at the solid–liquid and solid–air interfaces are in reasonable agreement with each other. Mixtures of the two enzymes show aggregates in which the complexes of the two enzymes are identifiable. This technique will make it possible to use STM to study the structure of protein systems at nearly physiological conditions and the nature of the interaction of proteins with surfaces.

ISSN:0734-211X    

DOI:10.1116/1.585212

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

This paper describes techniques used to image the cell sheath of the archaebacterium methanospirillum hungatei. Scanning tunneling microscope (STM) studies were done on hoop‐shaped components separated from the cell sheath by chemical treatment. High‐quality images were only obtained when the hoops were dispersed on highly oriented pyrolytic graphite and overcoated with a conductor, although hopping scans occasionally could image uncoated sheath fragments. Atomic force microscope (AFM) studies of the entire sheath showed the characteristic surface corrugation that was also seen in STM and in electron microscope images. We suggest that the STM imaging of any large biological structures may be limited principally by low electrical conductivity, although tip‐sample interactions and poor adhesion to the substrate also contribute to difficulties in the technique.

ISSN:0734-211X    

DOI:10.1116/1.585213

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The muscle glycogenolytic complex is responsible for providing access to the reserve carbohydrate energy stores in skeletal muscle during times of vigorous exercise. The complex is a set of enzymes and regulatory factors that are bound to the carbohydrate storage polymer, glycogen. These components provide the ordered synthesis and utilization of that stored form of glucose. Glycogen and the enzyme proteins, phosphorylase and phosphorylase kinase, have been imaged by atomic force microscopy (AFM) or scanning tunneling microscopy (STM). The images of all three generally correlated well with the known features of those molecules, as measured by traditional physicochemical methods. The exception for all three polymers is that the measured height by STM is in error. In each case, the molecules appear to be only about 30% of their true thickness, as measured by height above the graphite surface. It is clear that both AFM and STM will play important roles in biomedical investigation of macromolecular structures and complexes.

ISSN:0734-211X    

DOI:10.1116/1.585214

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We describe and give results for a metallic replica technique in which biological structures are first deposited on a flat graphite substrate and then overcoated with a thick metallic film. The metallic film is then peeled off the graphite, and its underside is imaged by the scanning tunneling microscope (STM), which shows indentation‐type replicas. We have used the technique on the cell sheath of the bacteriummethanospirillumHungatei, and find that the surface detail of the replica image is as good as that for a metal‐coated sheath. We also find that the biological structures stay in the indentations during the peeling‐off process, which gives the possibility of imaging bare structures that would normally be pushed along a flat substrate by the STM or atomic force microscope (AFM) tip.

ISSN:0734-211X    

DOI:10.1116/1.585215

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Conventional preparation techniques as used in electron microscopy have been used to separate chloroplasts. While still in a buffer solution they have been electrochemically deposited on a gold substrate. Scanning tunneling microscope images of the grana and lamellae of spinach chloroplasts have been found to be consistent with evidence from electron microscopy of their external structure. Possible contact sites, where proteins are imported selectively into the membrane, have been observed, some supporting linear molecular chains approximately 10 nm long.

ISSN:0734-211X    

DOI:10.1116/1.585216

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Atomic level structural and electronic analysis of titanium passivated by an oxide film is crucial for understanding the biocompatible properties of this transition metal. Scanning tunneling microscope (STM) images of electropolished titanium samples show a rather smooth surface in the nanometer range with structure attributed to surface defects induced by the electropolishing technique.I–Vspectra were performed with the STM using W, PtIr, and Au tips. These spectra completed by normalized conductivities spectra are compared and discussed in order to determine surface electronic properties of the oxide film and to estimate the influence of the STM tip. The surface band gap of this amorphous thin film mainly composed of TiO2is shifted to positive tip voltage and is similar to the one of ann‐type semiconductor with band bending bringing the valence band closer to the Fermi level. The surface band gap extends from −0.5 to +0.8 eV for a Au tip and from −0.1 to 0.7 eV for a W tip, which shows that W induces states in the band gap. Reproducible peaks in the local density of states of our Ti oxide surface appear both for Au and W tips at the same energies and are clearly apparent in the normalized conductivity curves.

ISSN:0734-211X    

DOI:10.1116/1.585217

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have examined two preparations of biomolecules labeled with colloidal gold markers using scanning tunneling microscopy. In the first preparation, we studied gold labeled IgG antibodies. In the second preparation, we studied unlabeled IgG antibodies which were complexed with gold labeled antigen (bovine serum albumin). Images of these noncrystalline biological specimens, obtained under atmospheric conditions, revealed features on a nanometer scale. The images show details of molecular organization in addition to the classical antibody configuration.

ISSN:0734-211X    

DOI:10.1116/1.585218

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Images of three different synthetic DNAs have been obtained by scanning tunneling microscopy (STM) following their deposition on graphite using a voltaic pulse. DNA applied to the STM tip is desorbed during a 4 V/10 μs pulse and deposited intact onto the surface of highly oriented pyrolytic graphite. Images of 22, 47, and 100 base‐pair molecules show that deposition occurs in close proximity to the tunneling tip and that the molecules appear to deposit singly or in highly oriented groups.

ISSN:0734-211X    

DOI:10.1116/1.585219

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy (STM) imaging has been performed on the HPI layer (hexagonally packed intermediate layer), freeze‐dried and coated with Pt–Ir–C. The HPI layer is a highly corrugated regular protein monolayer, found outermost in the cell wall of the bacterium Deinococcus radiodurans. The average structure of each of the two surface aspects of HPI layer has been determined from STM data using correlation averaging. The signal‐to‐noise ratio of the raw data obtained from STM of the HPI layer is in the range of 1.5 to 2, values much higher than those usually encountered in data obtained by transmission electron microscopy (TEM). In order to discuss reliability and accuracy of STM imaging, the reliefs obtained by STM are compared to reconstructed reliefs derived from TEM micrographs of freeze‐dried and metal‐coated specimens.

ISSN:0734-211X    

DOI:10.1116/1.585220

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Atomic force microscope (AFM) images of single‐stranded deoxyribonucleic acid (DNA) showing nucleotide resolution have been obtained using two sample preparation methods: DNA covalently attached to a polymerized lipid monolayer and then imaged under water and DNA on mica rinsed with a Ba(NO3)2solution and then imaged under ethanol. Some of the bases were identified in the AFM image of DNA on polymerized lipid. Current problems in sequencing DNA with the AFM include movement of the DNA during imaging and the difficulty of reproducing experiments.

ISSN:0734-211X    

DOI:10.1116/1.585221

出版商:American Vacuum Society    

年代:1991

数据来源: AIP