X-RAY-DIFFRACTION STUDIES OF THE STRUCTURAL ORGANIZATION OF PROLAMELLAR BODIES ISOLATED FROM ZEA-MAYS

Transmission electron microscopy (TEM) indicates that maize prolamella r bodies (PLBs) are built up of tetrapodal units based on a highly con voluted but continuous lipid bilayer exhibiting diamond cubic (Fd3m) s ymmetry. Such lattices are often described in terms of infinite period ic minimal surfaces (IMPS) exhibiting zero net curvature and dividing the system into two identical subvolumes. IT so, X-ray diffraction mea surements would bt: expected ci to index ore a double-diamond (Pn3m) l attice with a unit cell length half that of the TEM lattice. Our measu rements index on a Fd3m lattice with a similar repeat distance to thr TEM images. The PLB membrane is thus inherently asymmetric, probably a s the result of the distribution of membrane protein. (C) 1998 Federat ion of European Biochemical Societies.