THE PHYSIOLOGY AND BIOCHEMISTRY OF THE PROTEOLYTIC SYSTEM IN LACTIC-ACID BACTERIA

The inability of lactic acid bacteria to synthesize many of the amino acids required for protein synthesis necessitates the active functioni ng of a proteolytic system in those environments where protein constit utes the main nitrogen source. Biochemical and genetic analysis of the pathway by which exogenous proteins supply essential amino acids for growth has been one of the most actively investigated aspects of the m etabolism of lactic acid bacteria especially in those species which ar e of importance in the dairy industry, such as the lactococci. Much in formation has now been accumulated on individual components of the pro teolytic pathway in lactococci, namely, the cell envelope proteinase(s ), a range of peptidases and the amino acid and peptide transport syst ems of the cell membrane. Possible models of the proteolytic system in lactococci can be proposed but there are still many unresolved questi ons concerning the operation of the pathway in vivo. This review will examine current knowledge and outstanding problems regarding the prote olytic system in lactococci and also the extent to which the lactococc al system provides a model for understanding proteolysis in other grou ps of lactic acid bacteria.