Purification and characterization of a proteinase from Lactobacillus plantarum DPC2739

A proteinase from Lactobacillus plantarum DPC2739 was purified by a combination of ion exchange chromatography on DEAE-Sephacel and gel filtration on Sephacryl-S-300 HR and TSK G3000SW. The enzyme had properties typical of an alkaline serine proteinase. It was optimally active at pH 9.5 and between 45 and 50°C. The enzyme was monomeric with a molecular mass of ~ 42 kDa. It was strongly inhibited by phenylmethylsulphonyl fluoride, Cu²⁺ and Zn²⁺. The N-terminal amino acid sequence showed no homology with known Lactococcus or Lactobacillus proteinases. The proteinase hydrolysed both χ(s1)- and β-caseins at approximately the same rate.