Mediates the insertion of proteins targeted to the outer membrane of chloroplasts. Required for the import of protein precursors into chloroplasts. Forms the voltage-dependent preprotein translocation channels (hydrophilic beta barrel) of the TOC complex in the chloroplastic outer membrane. The narrowest inner diameter of this channel is approximately 14 Angstroms. Part of the TOC core complex that includes a protein for the specific recognition of transit peptides surrounded by a ring composed of four proteins forming translocation channels, and four to five GTP-binding proteins providing energy. This core complex can interact with components of the TIC complex to form a larger import complex. Chloroplastic protein precursors such as prSS (precursor of the RuBisCO small subunit) also interact with these complexes. TOC75 interacts with OEP14, TOC34/OEP34, TOC86/OEP86, TIC55, TIC110/IEP110 and CLPC. Mostly expressed in young leaves, also present in old leaves, roots and stems (at protein level). Transmembrane regions consist mainly of membrane-spanning sided beta-sheets, which are not predicted by sequence analysis tools. Belongs to the TOC75 family.