TISSUE-SPECIFIC DISTRIBUTION OF A PEROXISOMAL 46-KDA PROTEIN RELATED TO THE 58-KDA PROTEIN (STEROL CARRIER PROTEIN-X, STEROL CARRIER PROTEIN 2 3-OXOACYL-COA THIOLASE)/

The complete sequence of the nonspecific lipid-transfer protein (nsL-T P; sterol carrier protein 2) including the presequence is present at t he C-terminus (residues 405-547) of a 58-kDa protein. To be able to st udy this 58-kDa protein without the interference of nsL-TP, antibodies were raised against predicted epitope regions in the N-terminal part (peptide I, residues 23-43; peptide II, residues 130-149). Using these antibodies, rat tissues were analyzed by immunoblotting. In rat liver , in addition to the 58-kDa protein the antibody against peptide I (al pha-58K(23)) as well as the antibody against peptide II (alpha-58K(130 )) detected a 416-kDa protein. This suggests that both peptide sequenc es are present in this 46-kDa protein. Both the 46- and the 58-kDa-pro teins were abundantly present in liver and adrenals, but could also be detected in brain, kidney, heart, lung, testes, and ovary. This distr ibution. was observed in tissues from both male and female rats. Immun ogold labeling of cryosections of liver showed that alpha-58K(23) labe ls the peroxisomes. From double-labeling experiments using alpha-nsL-T P and alpha-58K(23) We conclude that the 46-kDa protein is peroxisomal , We propose that in the peroxisomes the protease that processes pre-n sL-TP also cleaves the 58-kDa protein giving rise to the 46-kDa protei n and nsL-TP. In addition to the 58- and 46-kDa proteins, an immunorea ctive 44-kDa protein was prominently present in rat heart and at low l evels also in small intestine and brain. Immunogold labeling of cryose ctions of heart and Western blotting of purified mitochondria showed t hat the 44-kDa protein is localized in the mitochondria. The 44-kDa pr otein was shown to be identical to mitochondrial sarcomeric creatine k inase, which has a peptide segment of five amino acid residues in comm on with peptide I. (C) 1996 Academic Press, Inc.