Part of a putrescine export transport system, does not play a role in resistance to antimicrobial peptides (PubMed:27803167). Does not stimulate K(+) uptake ability of TrkH on its own, but increases K(+) uptake by 20% in the presence of SapD; has no effect of TrkG (PubMed:11700350). Single mutation, decreased extracellular putrescine, in an sapBCDF operon deletion no change in resistance to antimicrobial peptide LL-37. Belongs to the ABC transporter superfamily.