Chromogenic Substrates


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What is a chromogenic Substrate?

Proteolytic Enzymes

Serine Proteases

Proteolytic Mechanism

Specificity and Selectivity

Enzyme Kinetics

Substrates in Practice

Selectivity Tables

Kinetic Tables

Protein Concentrations in Plasma

Theoretical Basis for Calculation

International Units and Enzyme Activity




Proteolytic enzymes

In the living organism, proteolytic enzymes (proteases) are produced to degrade and modify proteins. A main task for proteolytic enzymes is to degrade proteins into peptides or amino acids to be used either as an energy source or as building blocks for resynthesis of proteins. Furthermore, proteolytic enzymes modify cellular environments and facilitate cell migration in connection with wound repair and cancer, ovulation and implantation of the fertilized egg, embryonic morphogenesis, and involution of mammary glands after lactation.

Another important function of the proteases is their role as regulators in processes such as inflammation, infection and blood clotting. Most proteolytic enzymes are highly specific for their substrates. The classification of proteases, however, is not based on their choice of substrate but on their mechanism of action.

Four different groups of proteolytic enzymes, named after the active site amino acid residue responsible for the catalytic activity, are generally distinguished: the aspartic proteases (e.g. pepsin), the cystein proteases (e.g. cathepsin B and cathepsin H), the serine proteases (e.g. trypsin, thrombin and plasmin) and metalloproteases (e.g. collagenases and gelatinases).Although the members of each group of proteolytic enzymes may have very diverse biological functions, amino acid analysis often shows a high degree of structural similarity between them. Detailed knowledge of the structure and mechanism of action of one enzyme can in many cases reveal an understanding of the structure and functions of other enzymes within the same group.

Classes of proteases


active site

serine proteases

Ser His Asp*

cystein proteases

Cys His Asp*

aspartic proteases

Asp Asp

metallo proteases

His His Zn2+

*Asp not always present



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