There are three models that describe the insertion of porins into the outer mitochondrial membrane. The first model suggests that the beta-barrel precursors are folded outside the SAM channel and simultaneously inserted into the outer membrane. The second model proposes that the unfolded precursor passes through the SAM channel. After the subunits have been assembled, a mature porin is lifted over the lowest rim of the SAM channel and then inserted into the membrane. A third model suggests a conformational change in the beta-barrel subunit of the SAM complex called the SAM50. During precursor assembly, SAM50 unfolds its beta-barrel structure. Precursor beta-hairpins get assembled successively between the beta-strands of SAM50 using multiple hydrogen bonds. Hydrogen bond disruption provides the necessary energy for the complete assembly and insertion of the beta-barrel structures. Newly assembled porins are released into the outer mitochondrial membrane as the SAM50 returns to its closed barrel conformation.