Purification and Characterization of the Cell Wall Proteinase of Lactobacillus casei Subsp. casei IFPL 731 Isolated from Raw Goat's Milk Cheese

A cell wall proteinase from Lactobacillus casei subsp. casei IFPL 731 has been released in the presence of ethylenediaminetetraacetic acid and purified by ammonium sulfate precipitation, hydrophobic interaction, and ion exchange chromatography. Its molecular mass estimated by SDS−PAGE was about 150 kDa. Maximum activity was reached at pH 6.0 and 40 °C. Activity was completely inhibited by phenylmethanesulfonyl fluoride, suggesting that the enzyme belongs to the serine group of proteinases. It was very unstable even at 4 °C, and the Ca 2+ ion was ineffective as a stabilizing agent. It preferentially hydrolyzed β-casein and clove mainly bond 9−10 of the α s1 -casein(1−23) peptide. On the basis of its specificity toward caseins, an α s1 -casein(1−23) fragment, and two different charged chromophoric peptides, the proteinase can be classified as a mixed-type variant different from those identified with lactococcal proteinases.