Uteroferrin and intracellular tartrate-resistant acid phosphatases are the products of the same gene

Uteroferrin (Uf) is a purple acid phosphatase with a bi-iron center. It is the major secretory product of the porcine uterus under the influence of progesterone and supplies iron to the developing fetuses during pregnancy. Tartrate-resistant acid phosphatases (TRAP) are clearly similar to Uf in many of their properties but are generally located intracellularly in lysosomes. To determine whether Uf and intracellular TRAP are distinct gene products, cDNA for the TRAP from pig spleen were compared with Uf cDNA. Although no full-length cDNA for the former were isolated, a TRAP cDNA of 1.1 kilobases was identical in nucleotide sequence to a Uf cDNA (1.42 kilobases) in the region of overlap, which included the entire 3'-end of the transcript and most of the open reading frame. TRAP purified from porcine spleen also had an NH2-terminal amino acid sequence that corresponded to that of Uf purified from uterine secretions and was also similar in sequence to intracellular TRAP isolated from tissues of other species, including ones from human osteoclastomas and spleen. Finally, Southern hybridization analysis with two probes specific for exons 1 and 2 of the Uf gene strongly suggested the presence of only a single gene for acid phosphatases of this class in the pig. A similar analysis performed on human DNA with an exon-specific probe for human TRAP was also consistent with a single gene. It is concluded that the difference in trafficking between a secreted TRAP, such as Uf, and TRAP located in lysosomes is not the result of distinctive primary sequence of the polypeptides and that the variability within species ascribed to such enzymes is most likely the result of minor posttranslational.