obsolete receptor porin activity true receptor porin activity This term was made obsolete because it combines two functions that are not linked. OBSOLETE. A porin of the bacterial outer membrane that forms transmembrane pores and transports relatively large molecules from the external milieu to the periplasm in an energized process. Energizing of transport across the outer membrane requires a heterotrimeric complex of proteins, the TonB-ExbB-ExbD complex, or in some cases, the TolA-TolQ-TolR complex. Energizing requires proton motive force across the cytoplasmic membrane. GO:0015477 molecular_function