Exoenzyme
[6] The book "Intracellular Enzymes: A Course of Lectures Given in the Physiological," by Horace Vernon is thought to be the first publication using this word in that year.
[7] Based on the book, it can be assumed that the first known exoenzymes were pepsin and trypsin, as both are mentioned by Vernon to have been discovered by scientists Briike and Kiihne before 1908.
[3] Many gram-negative bacteria have injectisomes, or flagella-like projections, to directly deliver the virulent exoenzyme into the host cell using a type three secretion system.
Bacteria such as Staphylococcus aureus use the enzyme to form a layer of fibrin around their cell to protect against host defense mechanisms.
S. aureus can also produce staphylokinase, allowing them to dissolve the clots they form, to rapidly diffuse into the host at the correct time.
Bacteria such as Clostridium do so by using the enzyme to dissolve collagen and hyaluronic acid, the protein and saccharides, respectively, that hold tissues together.
These enzymes are grouped into three classes based on their amino acid sequences, mechanism of reaction, method of catalysis and their structure.
In humans, amylases are secreted by the pancreas and salivary glands, with both sources of the enzyme required for complete starch hydrolysis.
[19] Pectinases, also called pectolytic enzymes, are a class of exoenzymes that are involved in the breakdown of pectic substances, most notably pectin.
[26] This enzyme is responsible for the breakdown of large globular proteins and its activity is specific to cleaving the C-terminal sides of arginine and lysine amino acid residues.
[4] Optimizing the production of biofuels has been a focus of researchers in recent years and is centered around the use of microorganisms to convert biomass into ethanol.
The enzymes that are of particular interest in ethanol production are cellobiohydrolase which solubilizes crystalline cellulose and xylanase that hydrolyzes xylan into xylose.
[29] One model of biofuel production is the use of a mixed population of bacterial strains or a consortium that work to facilitate the breakdown of cellulose materials into ethanol by secreting exoenzymes such as cellulases and laccases.
[29] In addition to the important role it plays in biofuel production, xylanase is utilized in a number of other industrial and biotechnology applications due to its ability to hydrolyze cellulose and hemicellulose.
In this role, lipases are used to convert vegetable oil to methyl- and other short-chain alcohol esters by a single transesterification reaction.
[33] The role these enzymes play in these food applications is to partially breakdown the plant cell walls and pectin.
[33] Cellulases and hemicellulases are used in these industrial applications due to their ability to hydrolyze the cellulose and hemicellulose components found in these materials.
[34] In addition to the microorganisms ability to digest and absorb the pollutants, their secreted exoenzymes play an important role in many bioremediation strategies.
[35] Fungi have been shown to be viable organisms to conduct bioremediation and have been used to aid in the decontamination of a number of pollutants including polycyclic aromatic hydrocarbons (PAHs), pesticides, synthetic dyes, chlorophenols, explosives, crude oil, and many others.
Of particular interest in this field are bacterial hydrolases as they have an intrinsic low substrate specificity and can be used for numerous pollutants including solid wastes.
[37] Cell-free use of microbial exoenzymes as agents of bioremediation is also possible although their activity is often not as robust and introducing the enzymes into certain environments such as soil has been challenging.
