Purification, molecular cloning, and immunohistochemical localization of dipeptidyl peptidase II from the rat kidney and its identity with quiescent cell proline dipeptidase

We purified dipeptidyl peptidase II (DPP II) to homogeneity from rat kidney and determined its physicochemical properties, including its molecular wei ght, substrate specificity, and partial amino acid sequence. Furthermore, w e screened a rat kidney cDNA library, isolated the DPP II cDNA and determin ed its structure. The cDNA was composed of 1,720 base pairs of nucleotides, and 500 amino acid residues were predicted from the coding region of cDNA. Human quiescent cell proline dipeptidase (QPP) cloned from T-cells is a 58 -kDa glycoprotein existing as a homodimer formed with a leucine zipper moti f. The levels of amino acid homology were 92.8% (rat DPP II vs, mouse QPP) and 78.9% (rat DPP II vs. human QPP), while those of nucleotide homology we re 93.5% (rat DPP II vs. mouse QPP) and 79.4% (rat DPP II vs. human QPP). T he predicted amino acid sequences of rat DPP II and human and mouse QPP pos sess eight cysteine residues and a leucine zipper motif at the same positio ns. The purified DPP II showed similar substrate specificity and optimal pH to those of QPP. Consequently, it was thought that DPP II is identical to QPP. Northern blot analysis with rat DPP II cDNA revealed prominent express ion of DPP II mRNA in the kidney, and the order for expression was kidney > > testis greater than or equal to heart > brain greater than or equal to lu ng > spleen > skeletal muscle > liver. In parallel with Northern blot analy sis, the DPP II antigen was detected by immunohistochemical staining in the cytosol of epithelial cells in the kidney, testis, uterus, and cerebrum.