Biophysical Journal 39: 241-251 (1982)
© 1982 the Biophysical Society

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gruner, S M Articles by Clark, N A Search for Related Content PubMed PubMed Citation Articles by Gruner, S M Articles by Clark, N A

X-ray diffraction and electron microscope study of phase separation in rod outer segment photoreceptor membrane multilayers.

ABSTRACT

Phase separation in artificially stacked multilayers of isolated bovine retinal rod outer segment (ROS) membranes has been examined via x-ray diffraction and electron microscopy. Specimens were prepared by isopotential spin drying followed with partial hydration by equilibration against moist gas streams. Upon dehydration, the multilamellar membrane phase assumes a binary phase composition consisting of concentrated protein-containing lamellae interspersed with microdomains of hexagonally packed tubes of lipid in a HII configuration. The HII lattice is geometrically coupled to the lamellar phase with one set of hexagonal crystal planes co-planar to the local membrane lamellae. The hexagonal microdomains bear a striking resemblance to the "paracrystalline inclusions" observed in fast-frozen, intact frog ROS (Corless and Costello. 1981. Exp. Eye Res. 32:217). The lamellar lattice is characterized by an unusually small degree of disorder. Sharp lamellar diffraction with a 120 A unit cell is observed (at near total dehydration) to a resolution of 6 A. A model consistent with the data is that a multilamellar array of ROS disks is stable as long as the external disk surfaces are kept sufficiently far apart. If the distance between the membranes is allowed to shrink below a certain critical value, the disk lipids spontaneously convert to a nonbilayer phase. This suggests that the structure of the ROS is stabilized by an internal framework that acts to keep the disks apart from one another and from the plasmalemma. Thus, the necessity of avoiding phase separations may provide a rationale for the peculiar morphology of the ROS.

This article has been cited by other articles:

				D. P. Siegel, V. Cherezov, D. V. Greathouse, R. E. Koeppe II, J. A. Killian, and M. Caffrey Transmembrane Peptides Stabilize Inverted Cubic Phases in a Biphasic Length-Dependent Manner: Implications for Protein-Induced Membrane Fusion Biophys. J., January 1, 2006; 90(1): 200 - 211. [Abstract] [Full Text] [PDF]