Identification of a Ligand-Gated Ion Channel by Photoaffinity Labeling and Microsequencing

It is generally agreed that ion channels are operationally composed of two functional domains: The selectivity filter comprises the part of the protein that determines which ion may pass and which is retained; the gate determines under which conditions the selected ions may pass. Named according to the mechanisms that regulate the gate, the two groups of ion channels are today known as the ligandgated and the voltagegated channels.