Evidence against protein-induced 'internal pressure' in biological membranes. Partition of 8-anilinonaphthalene-1-sulphonate into Triton X-100 micelles and submitochondrial particles.

It has recently been proposed that although small amphiphilic molecules partition into phospholipid vesicles this partition is reduced by a factor of 10(3)-10(4)-fold by the presence of proteins in biological membranes [Conrad & Singer (1979) Proc. Natl. Acad. Sci. U.S.A.76, 5202-5206 and (1981) Biochemistry20, 808-818]. However, the affinity with which 8-anilinonaphthalene-1-sulphonate partitions into, or binds to, Triton X-100 micelles and submitochondrial particles is very similar and therefore does not support this proposal.