Characterization of peroxisomal Pex5p from rat liver - Pex5p in the Pex5p-Pex14p membrane complex is a transmembrane protein

Pex5p is the receptor for the vast majority of peroxisomal matrix proteins. Here, we show that about 15% of rat liver Pex5p is found in the peroxisoma l fraction representing 0.06% of total peroxisomal protein. This population of Pex5p displays all the characteristics of an intrinsic membrane protein . Protease protection assays indicate that this pool of Pex5p has domains e xposed on both sides of the peroxisomal membrane. The strong interaction of Pex5p with the membrane of the organelle is not affected by mild protease treatment of intact organelles, conditions that result in the partial degra dation of Pex13p. Cytosolic Pex5p is a monomeric protein. In contrast, virt ually all peroxisomal Pex5p was found to be part of a stable 250-kDa protei n assembly. This complex was isolated and shown to comprise just two subuni ts, Pex5p and Pex14p.