PARTIAL-PURIFICATION AND CHARACTERIZATION OF A CELL-WALL BOUND PROTEINASE FROM LACTOBACILLUS-CASEI

The cell wall-bound proteinase from Lactobacillus casei NCDO 151 was partially purified and characterized. Its properties appeared to be different from the two proteolytic components of the same strain described by Ezzat et al. (1988). The proteinase has pH optima at 4.8 using haemoglobin and at 5.6 with casein as substrate, temperature optimum at 35-37-degrees-C and is inactivated after 20 min at 50-degrees-C. The molecular weight, as estimated from molecular sieve chromatography, is approximately 150 000. Sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated a tetrameric composition. The isoelectric point is 4.8. Serine proteinase inhibitors strongly inhibit this enzyme, but also metal-chelating compounds affect its activity. The proteinase is thus to be regarded as a serine proteinase. The ions Ca2+ and Co2+ enchance proteinase activity, while Zn2+ and Cu2+ suppress it. The proteinase does not exhibit peptidase activity and it poorly degrades synthetic substrates of other serine proteinases.