X-RAY-SCATTERING IN THE PLANE OF MEMBRANE

We demonstrate a technique for measuring x-ray (or neutron) scattering with the momentum transfer oriented in the plane of a membrane, for t he purpose of studying the lateral organization of proteins and peptid es. As an example, the controversial question of whether gramicidin fo rms aggregates in membrane was investigated. We measured dilauroylphos phatidylcholine (DLPC) bilayers containing gramicidin in the molar rat io of 10:1. Very clear scattering curves reflecting gramicidin channel -channel correlation were obtained. Analysis of the data shows that th e channels were randomly distributed in the membrane. We suggest that oriented proteins may provide substantial x-ray contrast against the l ipid background without requiring heavy-atom labeling. This should ope n up many possible new experiments.