Download Methods in Membrane Biology by H. P. Zingsheim, H. Plattner (auth.), Edward D. Korn (eds.) PDF

By H. P. Zingsheim, H. Plattner (auth.), Edward D. Korn (eds.)

The contributions of electron microscopy to membrane biology were fundamental and, while, disappointing. Membranes have been identified to exist ahead of the appearance of electron microscopy and basic rules in their composition and molecular association have been deduced from permeability and electric conductivity measurements, polarized mild microscopy, and X-ray diffraction. however, the complexities of the numerous intracellular membranes and membranous organelles have been fairly no longer suspected until eventually they have been saw through the electron microscopist. One then had extra hopes that the excessive answer of the electron microscope (theoretically it may possibly get to the bottom of atomic distances) may let the visualization of the molecular structure of membranes and lead on to an less than­ status of constitution and serve as on the molecular point. This expectation has been principally unrealized. end result of the nice problems encountered within the training of organic fabric, a result of uncertainty of the chemistry of "staining," and thanks to a variety of electron optical artifacts, it's been an enormous problem simply to rationalize the saw photographs by way of the identified proof, not to mention to make use of the pictures to extend our wisdom of the molecular constitution of organic membranes. the numerous adjustments between membranes with recognize to operate and composition are misplaced within the common trilamellar photo. possibly the only significant exception to this, and the key structural contribution of electron microscopy on the molecular point, has come from freeze-etch electron microscopy.

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Riemersma (Riemersma and Booij 1962; Riemersma 1963, 1968) and Stoeckenius and Mahr (1965) notedwith a few exceptions-a stoichiometric I: 1 reaction of Os0 1 with double bonds. Infrared spectra show the formation of a cyclic monoester (Stoeckenius and Mahr, 1965) as shown in Scheme (II). Theoretically compound (23) could hydrolyze to form diols (24) and H 2 0s(VI)0 4 (25), as indicated Electron Microscopic Methods in Membrane Biology 31 by Criegee ( 1938). However, no indication of diol formation in biological materials was found by chromatography.

2), unless glutaraldehyde fixation is supplemented by postfixation with Os0 4 . To what extent does glutaraldehyde fixation affect membrane proteins? Structural and enzymatic changes have been investigated in a variety of enzyme preparations (for review, see Hopwood, 1972). When fixed with glutaraldehyde, a-chymotrypsin retains much of its enzymatic activity, although, according to light-scattering studies, small polymers are formed in a first step. , 1971 ). The formation of small polymers would, therefore, not be a reason for enzymatic inactivation.

Peracchia and Robertson (1971) reported an increased contrast of the outer electron-dense leaflet of nerve cell and organelle membranes upon electrical stimulation; they ascribe the effect to the "unmasking" of reactive sulfhydryl groups. According to circular dichroism measurements, a considerable proportion of the membrane proteins-which are originally in an a-helix-configuration-are unfolded during Os0 4 fixation (Lenard and Singer, 1968), although for these experiments an unusually high concentration (4%) of Os0 4 was used and experiments with 1% Os0 4 would have been more informative.

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