Microbial enzymes peptidases

Hydrolytic reactions are catalyzed by extracellular hydrolases and mineral surfaces (Chrost, 1990 Hoffman, 1990). For enzymatic reactions, a defined substrate or moiety must match the catalytic site of a specific enzyme. The most studied examples in aquatic systems are glycosidases, peptidases, and phosphatases (Munster and De Hann, 1998 see Chapter 13). In general, hydrolytic reactions break the relatively labile C—N and C—O bonds that link monomers, generating lower molecular weight products more suitable for microbial consumption. 

Cobalt, Co an essential bioelement present in traces in plants, animals and microorganisms. It is important as a constituent of vitamin B12. Traces of Co are required for microbial growth. It is a cofactor or prosthetic group of several enzymes, e.g. pyrophosphatases, peptidases, arginase, as well as certain enzymes involved in nitrogen fixation. 

Methods for eliminating bitter peptides in partial protein hydrolysates are known, but they cause a significant loss of essential amino acids. These procedures usually include additional enzymatic hydrolysis under controlled conditions (a shorter time for the hydrolysis leads to higher peptides that are not bitter) and a selection of suitable proteases, such as aminopeptidases, carboxypeptidases and some other proteases. Enzymes of plant and microbial origin have been successfully used for this purpose. For example, the intracellular peptidases from Lactococcus lactis ssp. cremoris and Brevibacterium linens, which have high proteolytic activity, successfully hydrolyse bitter peptides in cheeses. 

Few microbial proteases acting on n-peptides are known. The alkaline D-peptidase (ADP) from Bacillus cereus is related to Du-carboxypeptidase and p-lactamases. These enz unes have an accessible groove in which the nucleophilic serine and other catalytic amino acids are located. This n-peptidase could be applied for the synthesis of the 92-amino acid peptidyl prolyl cis-trans isomerase from Escherichia coli by condensation of two peptide fragments, of which the 35-amino acid acyl donor was activated as the OGp ester [62]. Thus the D-amino acid-selective enzyme was used for preparing a protein composed of L-amino acids and making the product insensitive to hydrolysis by the coupling enzyme. 

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