Abstract Dodecyl sulfate complexes of two soluble proteins, serum albumin and fumarase, have been “renatured” with large excesses of the nonionic detergent Triton X-100. The resulting complexes, essentially free of dodecyl sulfate, differ in their sedimentation properties relative to the native protein and in their interaction with Triton X-100. Albumin molecules refold to a form binding only very small amounts of Triton and have a sedimentation coefficient similar to that of the non-denatured protein. On the other hand, refolded fumarase molecules have a lower sedimentation coefficient than that of the native enzyme and bind up to 1.06 mg of Triton/mg protein. It is postulated that the fumarase molecule has been turned “inside-out” by the dodecyl sulfate/Triton treatment, and the implications of such large conformational changes for protein transport across membranes are discussed.