Partial characterization and comparison of cell wall proteinases from 5 strains of Streptococcus lactis

Cell wall proteinases from 5 strains of Streptococcus lactis including one S. lactis subsp.diacetylactis were compared and partially characterized.They shared sorne common enzymatic features: only one activity optimum at 30-40°C, at pH 5.5-6 on casein and 4-4.5 on haemoglobin.Crude cell wall extracts from the S. lactis strains were fully inhibited by DFP, but this inhibition was only partial for the S. lactis subsp.diacetylactis strain.Electrophoregrams of as!, {3 and K-casein hydrolysates obtained with the cell-wall extracts of these strains were quite similar for each protein substrate.{3-caseinwas preferentially broken down; as! and K-caseins were hydrolysed to a lesser extent.The production of proteolytic cell-wall activity was highly affected by the culture medium.The higher the peptide and/or calcium content of the medium, the lower the release of cell-wall proteinase.