Hydrodynamic properties of porin isolated from outer membranes of rat liver mitochondria.

The hydrodynamic properties of purified porin (Mr = 30 000), isolated from outer membranes of rat liver mitochondria has been studied. After gel filtration, active porin was eluted in a symmetrical peak with an estimated Stokes radius of 5.4 nm. The sedimentation coefficient (s) and partial specific volume (v) were found to be 2.6 S and 0.908 cm3/g, respectively, for the purified porin-Triton X-100 complex. Based on these determinations, a molecular weight of 170 000 for the porin-Triton X-100 complex was calculated. Correcting for bound Triton X-100, 1.8 g/g of protein, a molecular weight of 60 000 was estimated for the protein portion of the complex. Thus, isolated active porin appears to exist as a dimer.