Magnetic orientation of purple membranes demonstrated by optical measurements and neutron scattering.

Abstract

The observed magnetic orientation of retinal rod outer segments [l] , chloroplasts [2,3] and bacterial chromatophores [4] suggests that this magnetic property may be common to other biological membranes, perhaps even a general feature of membranes. This interesting phenomenon has already found considerable application in optical dichroism, X-ray diffraction and neutron diffraction studies of retinal rod outer segment membranes [S-8] and photosynthetic membranes [2-4,9-131. We report here investigations which demonstrate that the relatively planar pieces of purple membranes from Halobacterium halobium [ 14,151 also orient in magnetic fields. For membranes dispersed in water, orientation was first demonstrated by simple optical experiments with linearly polarized light. We observed both prominent birefringence and a degree of optical dichroism. The dichroism result, together with previous work which correlated optical dichroism and X-ray diffraction data from a specimen oriented by drying [ 151, strongly suggested that the orientation is with the planes of the