Imaging biological macromolecules

Imaging biological macromolecules in the transmission electron microscope requires several manipulations which may lead to difficulty in the interpretation of the results. The molecules imaged in the microscope column are far from the state in which they originally adsorbed to the material surface. The electron microscope operates under a vacuum of approximately 10 Torr. Material placed in the column is therefore dry. 

An experimental teclmique that is usefiil for structure studies of biological macromolecules and other crystals with large unit cells uses neither the broad, white , spectrum characteristic of Lane methods nor a sharp, monocliromatic spectrum, but rather a spectral band with AX/X 20%. Because of its relation to the Lane method, this teclmique is called quasi-Laue. It was believed for many years diat the Lane method was not usefiil for structure studies because reflections of different orders would be superposed on the same point of a film or an image plate. It was realized recently, however, that, if there is a definite minimum wavelengdi in the spectral band, more than 80% of all reflections would contain only a single order. Quasi-Laue methods are now used with both neutrons and x-rays, particularly x-rays from synclirotron sources, which give an intense, white spectrum. 

IMB Jena Image Library of Biological Macromolecules http //www.imb-jena.de/lMAGE.htmi... 

SIMS imaging was theoretically invented in 1949 by Herzog and Viehb of the Vienna University in Austria. The first SIMS device was completed by Liebel and Herzog in 1961 with the support of the National Aeronautics and Space Administration (NASA) and was used to analyze metal surfaces. However, it was not suitable for analyzing biological macromolecules because the second electronic ion beam breaks the molecules into atoms. 

Confocal scanning Examination of cells in Cryoelectron Imaging of biological macromolecules in the... 

A King. Image analysis and reconstruction in the electron microscopy of biological macromolecules. Chimica Scripta 14 245 -256, 1978-79. 

See, for example, the Jena library of biological macromolecules at www.fli-leibniz.de/IMAGE. html. 

Protein crystals are three-dimensionally ordered arrays of biological macromolecules. Although the dimensions of these crystals that sparkle and polarize light are measured in only tenths of millimeters, their ability to diffract X-rays provides the experimental data needed to image... 

The idea of increasing the signal-to-noise ratio in electron images of unstained biological macromolecules by averaging was dis-... 

The next milestone, in the history of NMR [Frel], was the extension of the NMR spectrum to more than one frequency coordinate. It is called multi-dimensional spectroscopy and is a form of nonlinear spectroscopy. The technique was introduced by Jean Jeener in 1971 [Jeel] with two-dimensional (2D) NMR. It was subsequently explored systematically by the research group of Richard Ernst [Em 1 ] who also introduced Fourier imaging [Kuml]. Today such techniques are valuable tools, for instance, in the structure elucidation of biological macromolecules in solution in competition with X-ray analysis of crystallized molecules as well as in solid state NMR of polymers (cf. Fig. 3.2.7) [Sch2]. 

The area detector is an electronic device for measuring many diffracted intensities at one time. It is a two-dimensional, position-sensitive detector that records the intensity of a Bragg reflection (diffracted beam) and its precise direction (as a location on the detector) it acts like an electronic substitute for film. This detection device is now used extensively for crystals of biological macromolecules. Such a detector may involve a multiwire proportional counter coupled to an electronic device or a television imaging system both devices permit a recording of the data in a computer-readable form. Alternatively, imaging plates may be used. These have phosphorescent material layered on them and store information on the extent of X-ray exposure until scanned bv a laser, when the intensity and location of the light then emitted is recorded. 

HI. Haggart, R., and Leaback, D. H., Determination of quantitative, luminogenic images of macromolecule components of biological cells and tissues. Anal Chim. Acta 227, 257-265... 

Structural mapping of adsorbate molecules by STM and AFM has been extended to biological macromolecules [49]. These include DNA [50], proteins, and protein complexes [51, and references therm). The natural medium for biological macromolecules is, however, aqueous solution, and water constitutes an integrated element of three-dimensional structure. High-resolution in-situ STM imaging of DNA [50], DNA bases [52], and metalloporphyrins [53] has been achieved recently, but obstacles arise for proteins ... 

---