Abstract
Abstract 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 m m but its activity levelled off at higher salt concentrations. Its complete inhibition was caused by 0.1 m m HgCl 2 , 1 m m SnCl 2 and 2.5 m m CuCl 2 . 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 β -casomorphin 1-4.
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