Properties and specificity of a cell-wall proteinase from Lactobacillus helveticus

Abstract

A cell-wall proteinase activity was extracted from cells of Lactobacillus helvetieus grown on MRS medium. The enzyme was characterized after DEAE-Trisacryl chrornatography and gel filtration on Ultrogel AcA 34 column. Two proteolytic fractions of different molecular weights were isolated. Their enzyme properties and specificity were clearly similar indicating that these fractions represented the same enzyme. It is a serine proteinase displaying optimum activity at pH 7.5-8.0 and 42 oc. Peptide bonds cleaved in œs l and {3casein had no corn mon feature and no clear specificity can be defined. The six main peptides obtained after {3-casein hydrolysis were identified (Arg.-Leug, HisI06-PheI19, LYS'~6-GlnlSZ' ArglsrPhel9o, LeuI9,-Valzo9' TyrI93-VaIZ09) as weil as the two peptides liberated from œs l-casein (Arg.-Ilec, Arg.-Glus). These peptides whose size varies between 6 and 19 residues have probably to be hydrolysed by membrane-bound peptidases prior to their transport through the cytoplasmic membrane. Sorne of those released from the Cterminal part of {3-casein are potentially bitter.