TCDB

The Transporter Classification Database (or TCDB) is an International Union of Biochemistry and Molecular Biology (IUBMB)-approved classification system for membrane transport proteins, including ion channels.

The upper level of classification and a few examples of proteins with known 3D structure:

They include a number of transmembrane -like proteins including (cytochrome bc1 ); ; formate dehydrogenase, respiratory nitrate reductase; succinate - coenzyme Q reductase (fumarate reductase); and succinate dehydrogenase. See electron transport chain.