Proteinases and Peptidases

Combinations of several enzymes with different specificities are required for complete degradation of proteins into free amino acids. Proteinases and peptidases are found not only in the gastrointestinal tract (see p. 268), but also inside the cell (see below). 

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). 

Gerhartz, B., Nistroj, A.J., and Demuth, H.U. 2002. Enzyme classes and mechanisms. In Proteinase and Peptidase Inhibition, Smith, H.J. and Simons, C., Eds. London Taylor Francis, pp. 1-20. 

Chemical and enzymatic methods for the selective cleavage of peptide bonds are not completely separate either-or propositions. In addition chemical modification may well be combined with enzymatic degradation in a manner which promises new usages and more selectivity for proteinases and peptidases in sequence studies. 

The esterase/lipase system of Lactococcus has received relatively little attention in comparison with its proteolytic system. Unlike the situation with lactococcal proteinases and peptidases, little is known about the genetics of lactoccal lipase/esterase. Isolation of lipase/esterase-negative variants of Lactococcus would permit the significance of these enzymes in cheese ripening to be assessed. 

Proteinases and peptidases from the secondary (adjunct) starter can play an important role in proteolysis in cheese varieties where such adjuncts... 

There are few studies on the proteinase and peptidase activities of Propionibacterium shermanii, the characteristic microorganism in Swiss cheese... 

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. 

The genetic code for cell-wall proteinase of lactococci as well as for some of the peptidases has been described (Kok, 1990). In the future, new mutants with other proteinase and peptidase profiles may be selected after genetic engineering, contributing further to our ability to control cheese quality and reducing the use of additives in the dairy industry. 

Hydrolytic enzymes are classed roughly according to the nature of the substrate acted upon. Proteinases and peptidases catalyze the following reaction ... 

While lipases play a major role in determining the flavor of many cheeses, proteolytic activities are often considered more important to the flavor of some hard cheeses, e.g., Cheddar. The use of proteinases becomes problematic since these enzymes often produce bitter peptides. Thus, the manufacturer typically has to use a balance of proteinases and peptidases the peptidases are necessary to break down the bitter peptides [59]. 

One important feature has been the prevention of racemization of amino acids. Numerous longer peptides, including peptide hormones, have recently been synthesized. Some synthetic peptides, being well-defined substrates, have served in the study of proteinases and peptidases. 

Protein respiration almost certainly involves first a hydrolytic breakdown by proteinases and peptidases to give free amino acids. Of the amino acids of plant cells, only glutamic acid is known to be actively oxidised by an enzyme universally distributed, the glutamic acid dehydrogenase ... 

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