C.R. Worthington

DIRECT STRUCTURE DETERMINATION OF MULTILAYERED MEMBRANE-TYPE SYSTEMS WHICH CONTAIN FLUID LAYERS

The theory of direct methods of structure analysis in the case of multilayered membrane-type systems which contain fluid layers is described. Diffraction formulas for this kind of analysis are derived. Deconvolution methods are used when the centrosymmetrical unit cells contain wide fluid layers. When the membrane systems contain narrow fluid layers, other direct methods are used. These direct methods involve computing either the Fourier series representations or the sampling theorem expressions.

The bilayer nature of deposits occurring in Gaucher's disease.

Abstract Evidence is presented for the structure of the Gaucher cell deposit existing as a series of bilayers that are each 60 A thick and are gradually twisted along their length. This evidence was obtained by freeze-etching studies and by X-ray diffraction studies that were used to calculate possible electron density profiles for each bilayer. A model is presented which shows the probable arrangement of the aggregated glucocerebroside molecules.

Direct Determination of the Lamellar Structure of Peripheral Nerve Myelin at Low Resolution (17 Å)

New X-ray diffraction data from normal nerve and nerve swollen in glycerol solutions have been recorded. Direct methods of structure analysis have been used in the interpretation of the X-ray data, and the phases of the first five orders of diffraction of peripheral nerve myelin have been uniquely determined. The direct methods include deconvolution of the autocorrelation function, sampling theorem reconstructions, and Fourier synthesis comparisons. Electron density profiles of normal and swollen nerve myelin at a resolution of 17 A together with an electron density scale in electrons per cubic angstrom are presented.

The structure of oriented sphingomyelin bilayers

X-ray diffraction from oriented bilayers of sphingomyelin gave up to 14 orders of diffraction of a lamellar repeat of 68.5 A on the merididan and up to eight reflections, including a strong reflection at 4.2 A, on the equator. The diffraction spacings did not change when the sphingomyelin bilayers were exposed to different humidities. A direct analysis of the low resolution X-ray data, using deconvolution is presented. A comparison of the Patterson functions of sphingomyelin with those of phosphatidylcholine and phosphatidylethanolamine suggests that the molecular structure of sphingomyelin in oriented bilayers resembles the structure of both phosphatidylcholine and phosphatidylethanolamine. Molecular model calculations for sphingomyelin bilayers have also been performed. Electron density profiles of sphingomyelin bilayers at resolution of about 6 A and about 2.5 A are presented. Our results indicate that the phosphorylcholine head group of sphingomyelin is in the plane of the membrane and at right angles to the hydrocarbon chains, the hydrocarbon chains are nearly parallel to each other, and there is only a limited, if any, interdigitation of the hydrocarbon chains of the adjacent sphingomyelin molecules in the bilayer.

X-ray diffraction evidence for the presence of discrete water layers on the surface of membranes

X-ray diffraction spacings in multilayered membranes obtained from frog sciatic nerves were found to increase in discrete steps of approx. 5 A during swelling. These observed jumps in the repeat period suggest that the lipid bilayers exist in distinct states of hydration, and perhaps the swelling occurs by step-wise addition of water layers between the polar head groups. Our analysis and statistical tests of this hypothesis are presented.

An X-ray study of the condensed and separated states of sciatic nerve myelin

Low-angle X-ray diffraction patterns of peripheral nerve myelin after modification by either rehydration in various solutions or by chemical treatment have been recorded. These X-ray patterns and the previously reported modified nerve myelin patterns demonstrate that nerve myelin has at least five different states: the normal state, condensed state I and II and separated state I and II. There are two membranes per unit cell in the normal state and in states II whereas there is one membrane per unit cell in states I. Under certain conditions normal nerve can go reversibly into either of states II. With continued treatment the nerve myelin structure moves irreversibly from state II to state I and, once in state I, the nerve myelin layers cannot return to the normal state. Our results demonstrate that there is a reversible transformation between condensed state I and separated state I. Fourier profiles of nerve myelin in the normal state, condensed state I and separated state I are presented.

How muscle may contact

Abstract A new molecular model is proposed for muscle contraction, that involves the electrical charging of the long (C-terminal) α-helical part of the head of the myosin molecule (S1) while the head is attached to actin; as it charges the α-helical part moves in the radial electric field between the filaments. The α-helical part snaps back when the myosin molecule is discharged electrically, at teh moment that ATP binds to the active enzymatic site. This snap-back model explains several puzzling phenomena in contractility, as well as providing a physical explanation for the origin of an impulsive force that drives muscle contraction.

The lamellar structure of nerve myelin after rehydration

Abstract New low-angle X-ray diffraction data have been obtained from nerve myelin after rehydration. The X-ray patterns show the first six orders of diffraction of a lamellar repeat unit of about 100 A. Direct methods of structure analysis have been used to determine uniquely the phases of the first three orders of diffraction. The electron density profile of rehydrated nerve myelin has been obtained on an absolute electron density scale and is compared with the electron density profile of normal nerve myelin at the same resolution of 16–17 A. Possible electron-density profiles of rehydrated nerve myelin at a resolution of 8 A are shown.

Electron density levels of sarcoplasmic reticulum membranes

Abstract Low-angle X-ray diffraction has been recorded from oriented preparations of sacroplasmic reticulum membranes in fluid media containing glycerol solutions in different concentrations. Discrete diffraction orders of a lamellar repeat distance ranging from 200 A to 250 A have been recorded. Fourier synthesis at a resolution of 17 A for 0, 10, 20, and 30% glycerol-treated sarcoplasmic reticulum membranes are described. An electron density scale in electrons/ A 3 for these Fourier syntheses has been determined. The question of the correctness of our asymmetric electron density profile for the sarcoplasmic reticulum membrane is critically examined. A study is made on the choice of phases and on the method used to process the X-ray intensities.

A biochemical study of the protein composition of frog sciatic nerve as a function of pH, heat treatment, and enzyme digestion

Abstract The protein compositions of peripheral nervous system myelin proteins from rat, rabbit, and frog Rana pipiens were examined by gel electrophoresis after discontinuous sucrose gradient purification. The major P 0 protein and the basic proteins P 1 and P 2 were shown to be doublets. Gel patterns of frog sciatic nerve after digestion in trypsin and Pronase are described. The peripheral nervous system myelin protein bands of frog sciatic nerve were unaffected by heat treatment to 65 °C. The effect of pH on frog sciatic nerve was studied over a pH range of 1.0 to 13.0 using gel electrophoresis and sedimentation in a continuous sucrose gradient. Phase transitions at acid pH below 2.5 and at alkaline pH above 11.5 were detected and studied. These phase transitions correlate with the different physical states of frog sciatic nerve previously reported by X-ray diffraction.