Rapid detection of DPP-IV activity in porcine serum: A fluorospectrometric assay

摘要

Dipeptidyl peptidase IV (DPP-IV) is an aminopeptidase that cleaves the N-terminal dipeptide from peptides bearing proline or alanine residues. Currently, DPP-IV activity is quantified by spectrophotometric or fluorometric methods, which employ Gly-Pro-pNA and Gly-Pro-AMC respectively, as substrate. However, these methods require high enzyme and substrate concentrations. In this study, we adapted the DPP-IV fluorospectrometric assay using NanoDrop 3300, which requires only nanogram levels of the enzyme (30 ng crude DPP-IV) and considerably low substrate concentrations (100 mu M). Fluorescence measurement required a reaction mixture of only 2 mu L, thus eliminating the need for microliter plates or cuvettes.We employed this assay to demonstrate DPP-IV activity in porcine serum for the first time. The enzymatic activity peaked at pH 8.0 in porcine (84 nM/min), human (87 nM/min) and bovine (89.1 nM/min) sera, with the optimum temperature of 37 degrees C. The enzyme showed maximum activity upon incubation for 40 min at 37 degrees C. In contrast, activity in the porcine serum was the highest after incubation for 30 min at the same optimized parameters. The IC50 values of diprotin A against DPP-IV from human, porcine, and bovine sera were 7.83, 8.62, 9.17 mu M, respectively. The present assay procedure is a convenient, sensitive, accurate and high-throughput method suitable for primary screening of DPP-IV inhibitors.