Pore‐forming activity in the outer membrane of the chloroplast envelope

The permeability properties of the outer membrane of the chloroplast envelope were studied. The exclusion limit for the penetration of molecules through this membrane into the intermembrane space lies between M r values of about 7000–13 000. This is the largest exclusion limit measured so far for pores of the porin type. In addition, the pore‐forming activity of the outer membrane of the chloroplast envelope was measured by reconstitution experiments. The pore has a single channel conductance of 0.72 nS, which is a linear function of the salt solution in the aqueous phase. The diameter of the chloroplast porin was calculated to be 2.5–3 nm, which is the largest diameter of all known porin pores, e.g., from mitochondria or Gram‐negative bacteria.