Proteases

Abstract

Proteases (also called peptidases, proteinases, or proteolytic enzymes) are enzymes that hydrolyze peptidyl bonds. They are of great importance in all physiological processes involving maturation and activation of proteins or their degradation (proteolysis) and are found in all biological kingdoms. Each protease is assigned to a family on the basis of a significant identity in amino-acid sequence, and to a clan which gathers families that display a common origin (Rawlings et al. 2006). Proteases are frequently classified according to their catalytic type, which is related to the chemical groups involved in the catalysis of the peptidyl bond. There are currently six clans of proteases. The better characterized clans are the serine proteases, the cysteine proteases, the aspartic proteases, and the metalloproteases. The "threonine proteases" and the "glutamyl proteases" clans contain only one family each. Identification of proteases in egg white encounters several difficulties due the presence of numerous antiproteases (see Chapter 8) that inhibit their enzymatic activity. No protease could be identified among the major proteins of egg white that have been already identified and characterized, which means that proteases must be present at very low concentration, as minor components, and are likely to be inhibited by antiproteases. To our knowledge, only two reports describe the isolation and the biochemical characterization of two different proteases named "glutamyl aminopeptidase" (Petrovic and Vitale 1990) and "methioninepreferring broad specificity aminopeptidase" (Skrtic and Vitale 1994). Genomic and amino acid sequences are not known and no identification can be made at this time. The biological role of these two proteases has not been investigated yet and no data has been reported as to their isolation from other biological fluids. According to their enzymatic activity, they could be members of the metalloprotease family, in which some such enzymes are known to participate in several processes involving tissue remodeling, such as embryogenesis. © Springer-Verlag Berlin Heidelberg 2007.