The major porin in this organism, forms a water-filled channel which favors the permeation of cations, amino acids, iron Fe(3+) and less efficiently phosphate. Does not transport Fe-ExoMS, the predominant siderophore. Plays a role in transport of beta-lactamase and hydrophilic fluoroquinolone antibiotics such as norfloxacin as well as chloramphenicol. There are about 2400 porins in wild-type, 800 in an mspA deletion and 150 in a double mspA-mspC deletion. Different conductance values with maxima at 2.3 and 4.6 nanosiemens might be caused by a simultaneous reconstitution of MspA channels into the membrane or by the existence of different MspA conformations.

> 85% as determined by SDS-PAGE.