Purification and partial characterisation of X-prolyl dipeptidyl aminopeptidase of Lactobacillus helveticus ITG LH1

A X-prolyl dipeptidyl aminopeptidase (EC 3.4.14.5, XPDAP) from Lactobacillus helveticus ITG LH1, a strain used for Swiss-type cheese, was purified by ion exchange and affinity chromatographies. The enzyme appeared to be a 140 kDa monomer. Optimal activity occurred at pH 7 and 40 C, but it was rapidly inactivated above 50 C. The enzyme was activated by NaCl and KCl up to 50-200 mM but its activity levelled off at higher salt concentrations. Its complete inhibition was caused by 0.1 mM HgCl2 1 mM SnCl2 and 2.5 mm CuCl2. It was inactivated by reagents specific for serine proteases, such as phenylmethylsulfonyl fluoride and sulfhydryl group-blocking reagents. The enzyme hydrolysed p-nitroanilide-substituted X-Pro and X-Ala dipeptides, as well as beta-casomorphin 1-4. (C) 2003 Elsevier Science Ltd. All rights reserved.