In the current study, we report the cloning and initial characterization of a novel human cytosolic aminopeptidase named adipocyte-derived leucine aminopeptidase (A-LAP). The sequence encodes a 941-amino acid protein with significant homology (43%) to placental leucine aminopeptidase (P-LAP)/oxytocinase. The predicted A-LAP contains the HEX-XH(X)18E consensus sequence, which is characteristic of the Ml family of zinc-metallopep-tidases. Although the deduced sequence contains a hydrophobic region near the N-terminus, the enzyme localized mainly in cytoplasm when expressed in COS-7 cells. Northern blot analysis revealed that A-LAP was expressed in all the tissues tested, some of which expressed at least three forms of mRNA, suggesting that the regulation of the gene expression is complex. When aminopeptidase activity of A-LAP was measured with various synthetic substrates, the enzyme revealed a preference for leucine, establishing that A-LAP is a novel leucine aminopeptidase with restricted substrate specificity. The identification of A-LAP, which reveals strong homology to P-LAP, might lead to the definition of a new subfamily of zinc-containing aminopeptidases belonging to the Ml family of metallopeptidases

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