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Marija Abramic, Detlev Schleuder, Ljerka Dolovcak, Werner Schröder, Kerstin Strupat, Dijana agi, Jasna Peter-Katalinic, Ljubinka Vitale

Human and Rat Dipeptidyl Peptidase III: Biochemical and Mass Spectrometric Arguments for Similarities and Differences

Dipeptidyl peptidase (DPP III) was purified from rat and human erythrocytes using an identical procedure. Electrophoretic analyses revealed the same molecular size and pI for both enzymes. The molecular mass of the human enzyme, measured by matrix-assisted laser desorption/ionization MS, was 82 500 ± 60 Da. Its tryptic peptide mass profile was determined using the same technique, and the amino acid sequence of two internal peptides was obtained by tandem MS and Edman degradation. A search of databases revealed a high similarity between the human erythrocyte and rat liver DPP III: 21 matches out of 34 detected peptides were found, covering 40% of the total sequence. Matched peptides included the peptide harboring the characteristic HELLGH sequence motif, and a stretch of 19 identical amino acids, containing Glu, a putative ligand of active site zinc.

Both enzymes preferred Arg-Arg-2-naphthylamide, and were activated by micromolar Co²⁺, differing in their pH optima and k_cat/K_m. Zn²⁺ ions, sulfhydryl reagents, and aminopeptidase inhibitors, especially probestin, inhibited the rat DPP III more potently. The two enzymes showed the highest affinity for angiotensin III (K_i <1?M) and a preference for a hydrophobic residue at the P₁ site. However, significant differences in the binding constants for several peptides indicated non-identity in the active site topography of human and rat erythrocyte DPP III.

Biological Chemistry, Walter de Gruyter

Print ISSN: 1431-6730
Volume: 381, 12/2000
Pages: 1233 - 1243

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