A farnesylated protein, Peroxin 19 (peroxisomal farnesylated protein, PxF or HK33), localizes to the outer surface of peroxisomes. Specifically, Peroxin 19 localizes to the cytoplasmic surface of peroxisomes in liver cells. Peroxin 19 is the human homolog of Pex19p, an oleic acid-inducible, farnesylated protein that is essential for peroxisome biogenesis in Saccharomyces cerevisiae. The carboxy-terminal part of Peroxin 19, including the CAAX homology box, is required for its biologic function. Moreover, Peroxin 19 is apparently involved in the initial stage of peroxisome membrane assembly, before the import of matrix protein.