The p13 porin (Ostberg et al. 2002). P13 displays a general (non-specific) channel-forming activity of 0.6 nanosiemens in 1 m KCl, has no preference for either cations or anions and shows no voltage-gating up to ±100 mV. The native P13 protein complex has a high molecular mass of about 300 kDa and is composed only of P13 monomers. The channel diameter was estimated to be about 1.4 nm with a 400-Da molecular mass cut-off (Bárcena-Uribarri et al. 2014).