Electron-beam induced conformation changes in polypeptide layers: an infrared study

Langmuir-Blodgett type polypeptide monolayers have been irradiated under conditions simulating the hazards of electron microscopic imaging. The damaging effect, i.e. the randomization of the alpha-helical layers, which occurs in the dose range between 50 and 200 e-/nm2, has been monitored by infrered dichroism.

Radiation damage of proteins in the solid state: changes of amino acid composition in catalase

Catalase has been irradiated with 100 keV electrons under conditions simulating the hazards of electron microscopic imaging. Amino acid analysis reveals a definite pattern of amino acid destruction which is well correlated with the particular chemical structures of amino acid side chains. This pattern appears to be distinctly different from the sensitivity pattern for monoamino acid systems, which fact is ascribed to intramolecular energy transfer and selective attack of liberated radicals.

Radiation damage in tripalmitin layers studied by means of infrared spectroscopy and electron microscopy

Structural deteriorations in biomembranes, as inevitably induced while structural information is gathered by electron optical methods, were evaluated by infrared spectroscopy. Tripalmitin model membranes were irradiated with 100 keV-electrons in an electron microscope. The intensity decay of group vibrations over the dose reveals the sequence of damage in the polar and nonpolar part of the molecule. The C-C backbone, being the most important structural feature, shows a significant latency effect up to 0.6 e-/A2 and is completely disordered by 3 e-/A2, corresponding to about three inelastic processes per molecule.

Inactivation of catalase monolayers by irradiation with 100 keV electrons

A catalase monolayer adsorbed on a layer of arachidic acid deposited on a solid support was irradiated with 100 keV electrons simulating the conditions of electron microscopic imaging. Effective doses were calculated taking into account the angular and energy distribution of backscattered electrons. Enzymatic inactivation was chosen as the criterion for damage and was monitored by a rapid and quantifiable but nevertheless sensitive assay. Dose-response curves revealed that inactivation is a one-hit-multiple-target phenomenon, which is consistent with biochemical evidence for a cooperative function of subunits. The experimentally determined target size coincides fairly well with both calculated cross sections for inelastic interactions based on the atomic composition of catalase and with calculated cross sections for ionizing events based on the chemical bonds involved. This legitimates both types of calculations even for complex biomolecules.

Relevance of three-dimensional reconstructions of stain distributions for structural analysis of biomolecules

The relevance of a three-dimensional model of a protein molecule is discussed in the context of artefacts which inevitably occur during the preparation and imaging process. It is emphasized that even under optimistic assumptions, there-construction of a structure complementary to a given spatial stain distribution cannot, at resolutions below 10-15 A, be regarded as being identical with the real protein structure.