Paracrystalline nature of myelin

Hybl, Albert

doi:10.1107/s0021889877013132

Cited by 11 publications

(8 citation statements)

References 8 publications

(10 reference statements)

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“…Hosemann (1951) applied his paracrystal theory to the interpretation of X-ray diffraction patterns from (t-and fl-keratin and from collagen. More recently the stacking of lipid bilayers in the myelin sheaths of nerves has been described as paracrystalline with disorder of the second kind (Blaurock & Nelander, 1976;Nelander & Blaurock, 1978;Hybl, 1976Hybl, , 1977. Collagen fibrils have recently been described as paracrystals by Hosemann, Dreissig & Nemetschek (1974).…”

Section: Introductionmentioning

confidence: 99%

Description of irregularity in biological structures

Woodhead-Galloway¹,

Young²,

Hukins³

1980

Acta Cryst Sect A

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A systematic theoretical analysis is made of the kinds of structural irregularity which occur in biological systems. The theoretical problems investigated were: (1) the precise meaning of the term 'paracrystar when applied to biological systems such as tropomyosin tactoids, collagen fibrils, keratin and the myelin sheath of nerve; (2) the relationship between the paracrystal and liquid-theory descriptions of disorder which have recently been applied to the structure of collagen fibrils; (3) how structural irregularity affects the diffraction patterns (X-ray, neutron and electron) which are commonly used to investigate the structure of these systems experimentally. The conclusions are: (I) paracrystalline disorder of the first kind refers to a spatially disordered crystal but for biological systems it would generally be impracticable to distinguish this from thermal disorder; (2) paracrystalline disorder of the second kind provides a conceptually clumsy method for describing liquid-like systems; (3) paracrystal models are not strictly valid for finite systems; (4) modern liquid theory, as applied, for example, to the structure of the collagen fibrils, provides an elegant and economical alternative to paracrystal theory for disorder of the second kind; (5) the presence of peaks in diffraction patterns from biological systems does not necessarily imply that the system has very much regularity, i.e. it is not evidence for the existence of a lattice.

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Section: Introductionmentioning

confidence: 99%

Description of irregularity in biological structures

Woodhead-Galloway¹,

Young²,

Hukins³

1980

Acta Cryst Sect A

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“…The assumption of a normal Gaussian distribution for the distance statistics is regarded as a first approximation. The analysis of Hybl (1977), based on the measurement of the thickness variances of the myelin lamellae from the electron micrograph of fixed myelin, suggests that the thickness distribution may not be normal. However, it is well established that fixation affects the stacking period and the lamellar thickness of myelin.…”

Section: Choice Of Gaussian Distribution For the Least-squares Refinementioning

confidence: 99%

“…Recent investigations (Blaurock & Nelander, 1976;Gbordzoe, 1977;Hybl, 1977) have shown that the nerve myelin membrane system in the swollen, fixed and, to some extent, even in the natural states shows considerable paracrystalline lattice distortions evident from electron micrographs, line broadening and variation of lattice constant with diffraction order in the intensity profiles of myelin samples.…”

Section: Introductionmentioning

confidence: 99%

Direct X-ray determination of the electron-density profile of the nerve myelin membrane, with paracrystalline lattice distortions taken into account

Gbordzoe¹,

Kreutz²

1978

J Appl Cryst

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Paracrystalline lattice distortions in the nerve myelin membrane system lead to the distortion of the Q function of the membrane stack and the Qo function of the unit cell. The Q function can be expressed as a convolution polynomial of the electron density distribution and the distance-statistics functions between neighbouring membranes. Fitting this model Q function to the experimental Q function in a non-linear least-squares refinement procedure, one obtains the electrondensity profile of the myelin stack and the distance-statistics functions. Elimination of the distance statistics permits the calculation of the undistorted Qo function, the deconvolution of which makes possible a unique determination of the electron density distribution of the unit cell.

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“…The presence of disorder in the nerve myelin membrane system has been receiving increased attention in the recent past: Hybl (1977), Blaurock & Nelander (1976), Gbordzoe (1977). Small-angle X-ray diffraction and electron-microscopical experiments, performed in the Institute of Biophysics and Radiation Biology, University of Freiburg im Breisgau, demonstrate that the two techniques may not lead to the same results, especially with regard to measuring the distance statistics in the system and determining the electron density distribution.…”

mentioning

confidence: 99%

Comments on the paracrystalline nature of myelin

Gbordzoe¹,

Kreutz²

1978

J Appl Cryst

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Varying degrees of distortion of the Q functions of myelin samples in different states – native, fixed, swollen, dehydrated etc. – suggest that disorder in the membrane system may appropriately be classified into intrinsic and nonintrinsic components. Quantitative estimates of the paracrystallinity in such biological systems (especially in the native state) from small‐angle X‐ray and neutron scattering experiments may not be directly correlated with similar measurements from electron microscopy. This is because preparative procedures for electron microscopy such as fixation and dehydration not only cause additional disorder but also induce in the membrane system structural changes which are not yet fully understood.

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Paracrystalline nature of myelin

Cited by 11 publications

References 8 publications

Description of irregularity in biological structures

Description of irregularity in biological structures

Direct X-ray determination of the electron-density profile of the nerve myelin membrane, with paracrystalline lattice distortions taken into account

Comments on the paracrystalline nature of myelin

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