CYTOCHROME-C-OXIDASE IN PROTEOLIPOSOMES VISUALIZED BY PLATINUM-CARBONAND BY TUNGSTEN-TANTALUM SHADOWING - IMAGE-ANALYSIS

Beef heart cytochrome c oxidase complexes incorporated into phospholip id liposomes were examined by freeze-fracture electron microscopy. Enz yme molecules are inserted into the membrane asymmetrically, with larg er projections on the 'C' side, where cytochrome c binding occurs, tha n on the 'M' (matrix-facing) side. Visualisation of the complexes was improved by: (i) image analysis, to determine details of size and shap e, and (ii) tungsten-tantalum (W/Ta) rather than platinum-carbon (Pt/C ) shadowing, which permits examination of smaller entities. Enzyme mol ecules are incorporated as dimers in the proteoliposomes. Some surface structural details of the embedded molecules can be discerned. Around each complex is seen a small area of modified lipid, the frozen annul us whose existence has been predicted with other methods. (C) 1994 Aca demic Press, Inc.