Proline-specific dipeptidyl peptidase-like (DPP IV; EC 3.4.14.5) activity in bovine serum has attracted little attention despite its ready availability and the paucity of useful proline-cleaving enzymes. Bovine serum DPP IV-like peptidase is very tolerant of organic solvents, particularly acetonitrile: upon incubation for 1 h at room temperature in 70% acetonitrile, 47% dimethylformainide, 54% DMSO and 33% tetrahydrofuran (v/v concentrations) followed by dilution into the standard assay mixture, the enzyme retained half of its aqueous activity. As for thermal performance in aqueous buffer, its relative activity increased up to 50 degrees C. Upon thermoin activation at 71 degrees C, pH 8.0 (samples removed periodically, cooled on ice, then assayed under optimal conditions), residual activities over short times fit a first-order decay with a k-value of 0.071 +/- 0.0034 min(-1). Over longer times, residual activities fit to a double exponential decay with k(1) and k(2) values of 0.218 +/- 10.025 min(-1) (46 +/- 4% of overall decay) and 0.040 +/- 0.002 min(-1) (54 +/- 4% of overall decay), respectively. The enzyme's solvent and thermal tolerances suggest that it may have potential for use as a biocatalyst in industry. Kinetic analysis with the fluorogenic substrate Gly-Pro-7-aminoiiiethylcoumarin over a range of pH values indicated two pK values at 6.18 +/- 0.07 and at 9.70 +/-0.50. We ascribe the lower value to the active site histidine; the higher may be due to the active site serine or to a free amino group in the substrate. (c) 2007 Elsevier Inc. All rights reserved.