We purified dipeptidyl peptidase II (DPP II) to homogeneity from rat kidney and determined its physicochemical properties, including its molecular weight, substrate specificity, and partial amino acid sequence. Furthermore, we screened a rat kidney cDNA library, isolated the DPP II cDNA and determined 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 eDNA. Human quiescent cell proline dipeptidase (QPP) cloned from T-cells is a 58-kDa glycoprotein existing as a homodimer formed with a leucine zipper motif. The levels of amino acid homology were 92.8% (rat DPP 11 vs. mouse QPP) and 78.9% (rat DPP II vs. human QPP), while those of nucleotide homology were 93.5% (rat DPP H vs. mouse QPP) and 79.4% (rat DPP 11 vs. human QPP). The predicted amino acid sequences of rat DPP H and human and mouse QPP possess eight cysteine residues and a leucine zipper motif at the same positions. The purified DPP II showed similar substrate specificity and optimal pH to those of QPP. Consequently, it was thought that DPP H is identical to QPP. Northern blot analysis with rat DPP II cDNA revealed prominent expression of DPP II mRNA in the kidney, and the order for expression was kidney _??_testis≥heart>brain≥lung>spleen>skeletal muscle≥liver. In parallel with Northern blot analysis, the DPP H antigen was detected by immunohistochemical staining in the cytosol of epithelial cells in the kidney, testis, uterus, and cerebrum.
The Japanese Biochemical Society