Cell-wall associated proteinase,

Although in vitro, the cell wall-associated proteinase of the Lactococcus starters is quite active on 8-casein (and that from some strains on asl-casein also), in cheese, they appear to act mainly on casein-derived peptides, produced by chymosin from asl-casein or by plasmin from / -casein. 

Cell wall-associated proteinases of Lactococcus can be classified into three groups, Pj-, Pm-, and mixed-type Pptype proteinases degrade /3- but not asi-casein at a significant rate, while Pm-type proteinases rapidly degrade both a- and /3-caseins (S. Visser etal., 1986). The nucleotide sequences... 

Lactic streptococci initiate casein degradation through the action of cell wall-associated and cell membrane-associated proteinases and peptidases. Small peptides are taken into the cell and hydrolyzed to their constituent amino acids by intracellular peptidases (Law and Sharpe 1978). Peptides containing four to seven residues can be transported into the cell by S. cremoris (Law et al. 1976B). S. lactis and S. cremoris have surface-bound peptidases and thus are not totally dependent on peptide uptake for protein use (Law 1979B). Some surface peptidases of S. cremoris are located in the cell membrane, whereas others are located at the cell wall-cell membrane interface (Exterkate 1984). Lactic streptococci have at least six different aminopeptidase activities, and can be divided into three groups based on their aminopeptidase profiles (Kaminogawa et al 1984). 

The predominant NSLAB in Cheddar and Dutch-type cheeses are meso-philic Lactobacillus, which possess a cell wall-associated and intracellular proteinases. A range of intracellular peptidases, including dipeptidases, aminopeptidases, and endopeptidases, have been identified in Lactobacillus (see reviews by Khalid and Marth 1990a Peterson and Marshall, 1990). Interestingly, carboxypeptidase activity, which has not been found in lacto-cocci, has been reported in Lactobacillus casei (El Soda et al., 1978). 

Gross proteolytic activity of lactic acid bacteria is the sum of proteinase and peptidase activity. Normally, proteinases are plasmid-encoded and the enzymes are, in most cases, associated with the cell wall by a calcium ion-dependent binding. The synthesis of proteinase seems to be regulated by the growth medium (Exterkate, 1985 Bruinenberg et al., 1992). Normally, milk as growth medium forces strains to produce a high level of proteinase. 

It is helpful in the effort to understand activation complexes to consider complex formation, the reactions that occur in the complexes, and the demise of the complexes as proceeding in a sequence. First, a reversible, noncovalent association of proteinase, cofactor protein (strictly, activated cofactor protein), proteinase precursor, and membrane surface occurs to form the activation complex. This spontaneous association occurs as the result of complementary interaction sites on the protein molecules, e.g., the binding sites between proteinase and protein substrate, proteinase and cofactor protein, substrate and cofactor protein, and all three proteins with the membrane surface. Tissue factor normally exists as an integral membrane protein and is always associated with the membranes of cells in the vessel wall. The same processes are involved in the anticoagulant subsystem and, with a different surface, fibrin in the fibrinolytic system as well. 

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