Characterization of a porin from Mycobacterium smegmatis.

A pore-forming protein with an Mr of 40,000 has been extracted from the cell wall of Mycobacterium smegmatis with buffer containing the detergent Zwittergent 3-12 and 0.5 M NaCl and purified on an anion-exchange column. Although the pore diameter was large (2 nm), the specific activity was much lower than those of nonspecific porin channels of enteric bacteria. The channel allowed the permeation of small hydrophilic molecules such as sugars and amino acids. Its N-terminal sequence did not show any similarity to those of other porins sequenced so far.