Probable outer membrane component of the TtgABC efflux pump with unknown specificity. Belongs to the outer membrane factor (OMF) (TC 1.B.17) family. There are 4 nearly identical operons in various strains of P.putida. The ttgABC operon of strain DOT-T1E and the mepABC operon of strain KT2442-TOL function in solvent and antibiotic efflux; however in strain S12 the arpABC operon functions only in antibiotic efflux. This may be due to different protein expression levels. In KT2400 this operon does not seem to function in toluene efflux.