ATOMIC-FORCE MICROSCOPY OBSERVATIONS OF ACYL CHAINS IN PHOSPHOLIPIDS

The potential use of atomic force microscopy (AFM) to image the mode o f assembly and to measure the corresponding lattice parameters of mode l systems consisting of ordered aggregates of cardiolipin molecules ha s been investigated. An unprecedented resolution of about 0.2 nm has b een achieved on suitably prepared specimens. This enables the orientat ional order and the positional correlations of the individual molecule s in the lattice to be defined, and submolecular details, such as the acyl chains and the polar groups, to be imaged. The structural paramet ers derived from AFM have been compared with those obtained by transmi ssion electron diffraction of the same specimen and found to be in exc ellent agreement. AFM turns out to be a powerful, and probably a uniqu e tool to reveal local phase variations in systems, such as biological membranes, that have non-homogeneous composition and organization.