Enables the transfer of a substance, usually a specific substance or a group of related substances, from one side of a membrane to the other. [GOC:jid, GOC:mtg_transport, ISBN:0815340729]
The component of a membrane consisting of the gene products and protein complexes having at least some part of their peptide sequence embedded in the hydrophobic region of the membrane. [GOC:dos, GOC:go_curators]
The directed movement of charged atoms or small charged molecules into, out of or within a cell, or between cells, by means of some agent such as a transporter or pore. [GOC:ai]