Editing Exoenzyme

{{Short description|Enzyme that functions outside the cell it is secreted from}}
[[File:Organelles of the Secretory Pathway.png|thumb|upright=1.5|Organelles of the secretory pathway involved in the secretion of exoenzymes]]

An '''exoenzyme''', or '''extracellular enzyme''', is an [[enzyme]] that is secreted by a [[cell (biology)|cell]] and functions [[extracellular|outside that cell]]. Exoenzymes are produced by both [[prokaryotic]] and [[eukaryotic]] cells and have been shown to be a crucial component of many [[biological process]]es. Most often these enzymes are involved in the breakdown of larger [[macromolecule]]s. The breakdown of these larger macromolecules is critical for allowing their constituents to pass through the [[cell membrane]] and enter into the cell. For [[human]]s and other complex organisms, this process is best characterized by the [[digestive system]] which breaks down solid [[nutrients|food]]<ref>{{cite journal |vauthors= Kong F, Singh RP |title= Disintegration of solid foods in human stomach |journal= Journal of Food Science |volume= 73 |issue= 5 |pages= R67–80 |date= June 2008 |pmid= 18577009 |doi= 10.1111/j.1750-3841.2008.00766.x|doi-access= free }}</ref> via exoenzymes. The small molecules, generated by the exoenzyme activity, enter into cells and are utilized for various cellular functions. [[Bacteria]] and [[fungi]] also produce exoenzymes to [[digestion|digest]] [[nutrient]]s in their [[environment (biophysical)|environment]], and these organisms can be used to conduct laboratory [[assay]]s to identify the presence and function of such exoenzymes.<ref name=assays/> Some [[pathogenic]] species also use exoenzymes as [[virulence factor]]s to assist in the spread of these [[pathogen|disease-causing]] [[microorganism]]s.<ref name=virulence/> In addition to the integral roles in biological systems, different classes of [[microorganism|microbial]] exoenzymes have been used by humans since [[prehistory|pre-historic times]] for such diverse purposes as [[food processing|food production]], [[biofuel]]s, [[textile manufacturing|textile production]] and in the [[pulp and paper industry|paper industry]].<ref name=geobiology>{{cite book |last=Thiel|first=ed. by Joachim Reitner, Volker|title=Encyclopedia of geobiology|publisher=Springer|location=Dordrecht|isbn=9781402092121|pages=355–359}}</ref> Another important role that microbial exoenzymes serve is in the natural ecology and [[bioremediation]] of [[ecoregion#Terrestrial|terrestrial]] and [[ecoregion#Marine|marine]]<ref>{{cite journal |vauthors= Arnosti C |title= Microbial extracellular enzymes and the marine carbon cycle |journal= Annual Review of Marine Science |volume= 3 |issue= 1 |pages= 401–25 |date= 15 January 2011 |pmid= 21329211 |doi= 10.1146/annurev-marine-120709-142731|bibcode= 2011ARMS....3..401A }}</ref> environments.

==History==
Very limited information is available about the original discovery of exoenzymes. According to [[Merriam-Webster]] dictionary, the term "exoenzyme" was first recognized in the English language in 1908.<ref name=Dictionary>{{cite web |title=Merriam-Webster|url=https://www.merriam-webster.com/dictionary/exoenzyme|accessdate=2013-10-26}}</ref> 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.<ref name=Lexic>{{cite web |title=Lexic.us|url=https://www.lexic.us/definition-of/exoenzymes|accessdate=2013-10-26}}</ref> 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.<ref name="history">{{cite web |last=Vernon|first=Horace|title=Intracellular Enzymes: A Course of Lectures Given in the Physiological|url=https://archive.org/stream/intracellularen00verngoog/intracellularen00verngoog_djvu.txt|accessdate=2013-10-26}}</ref>

==Function==
In [[bacteria]] and [[fungi]], exoenzymes play an integral role in allowing the organisms to effectively interact with their environment. Many bacteria use digestive enzymes to break down nutrients in their surroundings. Once digested, these nutrients enter the bacterium, where they are used to power cellular pathways with help from [[endoenzyme]]s.<ref name="bacteria exoenzymes">{{cite web|last=Kaiser|first=Gary|title=Lab 8: Identification of Bacteria Through Biochemical Testing|url=http://faculty.ccbcmd.edu/courses/bio141/labmanua/lab8/lab8.html|work=Biol 230 Lab Manual|accessdate=9 December 2013|archive-date=11 December 2013|archive-url=https://web.archive.org/web/20131211073425/http://faculty.ccbcmd.edu/courses/bio141/labmanua/lab8/lab8.html|url-status=dead}}</ref>

Many exoenzymes are also used as [[virulence factor]]s. [[Pathogen]]s, both bacterial and fungal, can use exoenzymes as a primary mechanism with which to cause [[disease]].{{citation needed|date=April 2021}} The [[metabolic activity]] of the exoenzymes allows the bacterium to invade [[host (biology)|host]] organisms by breaking down the host cells' defensive outer layers or by [[necrotizing]] body [[tissue (biology)|tissue]]s of larger organisms.<ref name=virulence>{{cite book |last=Duben-Engelkirk|first=Paul G. Engelkirk, Janet|title=Burton's microbiology for the health sciences|year=2010|publisher=Wolters Kluwer Health/Lippincott Williams & Wilkins|location=Philadelphia|isbn=9781605476735|pages=173–174|edition=9th}}</ref> Many [[gram-negative bacteria]] have [[injectisome]]s, or [[flagella]]-like projections, to directly deliver the virulent exoenzyme into the host cell using a [[type three secretion system]].<ref name="type III sec">{{cite journal |vauthors= Erhardt M, Namba K, Hughes KT |title= Bacterial nanomachines: the flagellum and type III injectisome |journal= Cold Spring Harbor Perspectives in Biology |volume= 2 |issue= 11 |pages= a000299 |date= November 2010 |pmid= 20926516 |doi= 10.1101/cshperspect.a000299 |pmc=2964186}}</ref> With either process, pathogens can attack the host cell's structure and function, as well as its nucleic DNA.<ref>{{cite journal |vauthors= McGuffie EM, Fraylick JE, Hazen-Martin DJ, Vincent TS, Olson JC |title= Differential sensitivity of human epithelial cells to Pseudomonas aeruginosa exoenzyme S |journal= Infection and Immunity |volume= 67 |issue= 7 |pages= 3494–503 |date= July 1999 |doi= 10.1128/IAI.67.7.3494-3503.1999 |pmid= 10377131 |pmc=116536}}</ref>

In [[eukaryotic]] cells, exoenzymes are manufactured like any other [[enzyme]] via [[protein synthesis]], and are transported via the [[secretory pathway]]. After moving through the [[rough endoplasmic reticulum]], they are processed through the [[Golgi apparatus]], where they are packaged in [[vesicle (biology and chemistry)|vesicles]] and released out of the cell.<ref name="sec path">{{cite book |last=Lodish|first=Harvey|title=Molecular cell biology|year=2008|publisher=Freeman|location=New York [u.a.]|isbn=978-0716776017|edition=6th ed., [2nd print.].}}</ref> In [[human]]s, a majority of such exoenzymes can be found in the [[digestive system]] and are used for [[metabolic]] breakdown of [[macronutrient]]s via [[hydrolysis]]. Breakdown of these nutrients allows for their incorporation into other [[metabolic pathway]]s.<ref>{{cite web |last=Andrews|first=Lary|title=Supplemental Enzymes for Digestion|url=http://www.donttouchme.com/web/sites/enzymesinc/enzymeswhitepaper/hhr_paper.html|work=Health and Healing Research|accessdate=9 December 2013|url-status=dead|archive-url=https://web.archive.org/web/20130727190532/http://www.donttouchme.com/web/sites/enzymesinc/enzymeswhitepaper/hhr_paper.html|archive-date=27 July 2013}}</ref>

==Examples of exoenzymes as virulence factors==

Source:<ref name=virulence/>

[[File:Necrotizing fasciitis - intermed mag.jpg|200px|thumbnail|right|Microscopic view of necrotizing fasciitis as caused by ''Streptococcus pyogenes'']]

===Necrotizing enzymes===
[[Necrotizing]] enzymes destroy cells and tissue. One of the best known examples is an exoenzyme produced by ''[[Streptococcus pyogenes]]'' that causes [[necrotizing fasciitis]] in humans.

===Coagulase===
By binding to [[prothrombin]], [[coagulase]] facilitates [[clotting]] in a cell by ultimately converting [[fibrinogen]] to [[fibrin]]. Bacteria such as ''[[Staphylococcus aureus]]'' use the enzyme to form a layer of fibrin around their cell to protect against host [[defense mechanism]]s.
{{Clear}}
[[File:Staphylococcus aureus, 50,000x, USDA, ARS, EMU.jpg|175px|thumbnail|left|Fibrin layer formed by ''Staphylococcus aureus'']]

===Kinases===
The opposite of coagulase, [[kinase]]s can dissolve clots. ''S. aureus'' can also produce staphylokinase, allowing them to dissolve the clots they form, to rapidly diffuse into the host at the correct time.<ref>{{cite web |last=Todar|first=Kenneth|title=Mechanisms of Bacterial Pathogenicity|url=http://textbookofbacteriology.net/pathogenesis_4.html|work=Todar's Online Textbook of Bacteriology|publisher=Kenneth Todar, PhD|accessdate=12 December 2013}}</ref>

===Hyaluronidase===
Similar to collagenase, [[hyaluronidase]] enables a pathogen to penetrate deep into tissues. 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.

===Hemolysins===
[[Hemolysin]]s target erythrocytes, a.k.a. [[red blood cell]]s. Attacking and [[lysing]] these cells harms the host organism, and provides the microorganism, such as the fungus ''[[Candida albicans]]'', with a source of iron from the lysed [[hemoglobin]].<ref>{{cite journal |vauthors= Favero D, Furlaneto-Maia L, França EJ, Góes HP, Furlaneto MC |title= Hemolytic factor production by clinical isolates of Candida species |journal= Current Microbiology |volume= 68 |issue= 2 |pages= 161–6 |date= February 2014 |pmid= 24048697 |doi= 10.1007/s00284-013-0459-6|s2cid= 253807898 }}</ref> Organisms can either by [[alpha-hemolytic]], [[beta-hemolytic]], or [[hemolysis (microbiology)#Gamma|gamma]]-hemolytic (non-hemolytic).
{{Clear}}

==Examples of digestive exoenzymes==
===Amylases===
[[File:Pancreatic alpha-amylase 1HNY.png|150px|thumb|Pancreatic alpha-amylase 1HNY]]
[[Amylase]]s are a group of extracellular enzymes ([[glycoside hydrolase]]s) that catalyze the [[hydrolysis]] of [[starch]] into [[maltose]]. These enzymes are grouped into three classes based on their [[amino acid]] sequences, mechanism of reaction, method of [[catalysis]] and their structure.<ref>{{cite journal |last1= Sharma |first1= Archana |first2= T. |last2= Satyanarayana |name-list-style= vanc |title= Microbial acid-stable alpha-amylases: Characteristics, genetic engineering and applications|journal=Process Biochemistry|year=2013|volume=48 |issue= 2 |pages=201–211|doi=10.1016/j.procbio.2012.12.018}}</ref> The different classes of amylases are [[α-amylase]]s, [[β-amylase]]s, and [[glucoamylase]]s. The α-amylases hydrolyze starch by randomly cleaving the 1,4-a-D-glucosidic linkages between [[glucose]] units, β-amylases cleave non-reducing chain ends of components of starch such as [[amylose]], and glucoamylases [[hydrolyze]] glucose molecules from the ends of amylose and [[amylopectin]].<ref name="pmid10744959">{{cite journal |vauthors= Pandey A, Nigam P, Soccol CR, Soccol VT, Singh D, Mohan R |title= Advances in microbial amylases |journal= Biotechnol. Appl. Biochem. |volume= 31 |issue= 2| pages= 135–52 |year= 2000 |pmid= 10744959 |doi=10.1042/ba19990073}}</ref> Amylases are critically important extracellular enzymes and are found in plants, animals, and [[microorganism]]s. In humans, amylases are secreted by the pancreas and salivary glands, with both sources of the enzyme required for complete starch hydrolysis.<ref>{{cite journal |last=Pandol|first=Stephen|title=The Exocrine Pancreas|journal=Colloquium Series on Integrated Systems Physiology: From Molecule to Function |year=2010 |volume=3 |issue=2 |pages=1–64 |url=https://www.ncbi.nlm.nih.gov/books/NBK54128/|publisher=Morgan & Claypool Life Sciences|doi=10.4199/C00026ED1V01Y201102ISP014 |pmid=21634067 |accessdate=25 November 2013}}</ref>

===Lipoprotein lipase===
[[Lipoprotein lipase]] (LPL) is a type of [[digestive enzyme]] that helps regulate the uptake of [[triacylglycerol]]s from [[chylomicron]]s and other low-density [[lipoprotein]]s from fatty tissues in the body.<ref name=Mead>{{cite journal |vauthors= Mead JR, Irvine SA, Ramji DP |title= Lipoprotein lipase: structure, function, regulation, and role in disease |journal= Journal of Molecular Medicine |volume= 80 |issue= 12 |pages= 753–69 |date= December 2002 |pmid= 12483461 |doi= 10.1007/s00109-002-0384-9|s2cid= 40089672 }}</ref> The exoenzymatic function allows it to break down the triacylglycerol into two [[free fatty acid]]s and one molecule of [[monoacylglycerol]]. LPL can be found in [[endothelial cell]]s in fatty tissues, such as [[adipose tissue|adipose]], [[cardiac]], and [[muscle]].<ref name=Mead/> Lipoprotein lipase is downregulated by high levels of [[insulin]],<ref>{{cite journal |vauthors= Kiens B, Lithell H, Mikines KJ, Richter EA |title= Effects of insulin and exercise on muscle lipoprotein lipase activity in man and its relation to insulin action |journal= The Journal of Clinical Investigation |volume= 84 |issue= 4 |pages= 1124–9 |date= October 1989 |pmid= 2677048 |pmc= 329768 |doi= 10.1172/JCI114275}}</ref> and upregulated by high levels of [[glucagon]] and [[adrenaline]].<ref name=Mead/>

===Pectinase===
[[Pectinase]]s, also called [[pectolytic]] [[enzyme]]s, are a class of exoenzymes that are involved in the breakdown of [[pectic]] substances, most notably [[pectin]].<ref>{{cite journal |last=Jayani|first=Ranveer Singh|author2=Saxena, Shivalika |author3=Gupta, Reena |title=Microbial pectinolytic enzymes: A review|journal=Process Biochemistry|date=1 September 2005|volume=40|issue=9|pages=2931–2944|doi=10.1016/j.procbio.2005.03.026}}</ref> Pectinases can be classified into two different groups based on their action against the [[galacturonan]] backbone of pectin: de-esterifying and depolymerizing.<ref>{{cite journal |last=Alimardani-Theuil|first=Parissa|author2=Gainvors-Claisse, Angélique |author3=Duchiron, Francis |title=Yeasts: An attractive source of pectinases—From gene expression to potential applications: A review|journal=Process Biochemistry|date=1 August 2011|volume=46|issue=8|pages=1525–1537|doi=10.1016/j.procbio.2011.05.010}}</ref> These exoenzymes can be found in both plants and [[microbial]] organisms including [[fungi]] and [[bacteria]].<ref>{{cite journal |last=Gummadi|first=Sathyanarayana N.|author2=Panda, T.|title=Purification and biochemical properties of microbial pectinases—a review|journal=Process Biochemistry|date=1 February 2003|volume=38|issue=7|pages=987–996|doi=10.1016/S0032-9592(02)00203-0}}</ref> Pectinases are most often used to [[Chemical decomposition|break down]] the pectic elements found in plants and plant-derived products.

===Pepsin===
Discovered in 1836, [[pepsin]] was one of the first enzymes to be classified as an exoenzyme.<ref name=history/> The enzyme is first made in the inactive form, [[pepsinogen]] by [[Gastric chief cell|chief cell]]s in the lining of the [[stomach]].<ref name=Encyclo>{{cite web |title=Encyclopædia Britannica|url=https://www.britannica.com/science/pepsin|accessdate=November 14, 2013}}</ref> With an impulse from the [[vagus nerve]], pepsinogen is [[secreted]] into the stomach, where it mixes with [[hydrochloric acid]] to form pepsin.<ref>{{cite journal |vauthors= Guldvog I, Berstad A |title= Physiological stimulation of pepsin secretion. The role of vagal innervation |journal= Scandinavian Journal of Gastroenterology |volume= 16 |issue= 1 |pages= 17–25 |year= 1981 |pmid= 6785873}}</ref> Once active, pepsin works to break down proteins in foods such as [[dairy]], [[meat]], and [[egg (food)|egg]]s.<ref name="Encyclo"/> Pepsin works best at the [[pH]] of [[gastric acid]], 1.5 to 2.5, and is deactivated when the acid is [[neutralization (chemistry)|neutralized]] to a pH of 7.<ref name="Encyclo"/>

===Trypsin===
Also one of the first exoenzymes to be discovered, [[trypsin]] was named in 1876, forty years after pepsin.<ref name="tryp general">{{cite web |last=Worthington|first=Krystal|title=Trypsin|url=http://www.worthington-biochem.com/TRY/|work=Worthington Biochemical Corporation|accessdate=26 November 2013}}</ref> This enzyme is responsible for the breakdown of large [[globular protein]]s and its activity is specific to cleaving the [[C-terminal]] sides of [[arginine]] and [[lysine]] [[amino acid residue]]s.<ref name="tryp general"/> It is the derivative of [[trypsinogen]], an inactive precursor that is produced in the [[pancreas]].<ref name=dic>{{cite web |title=Trypsin|url=https://www.thefreedictionary.com/trypsinogen|publisher=Free Dictionary|accessdate=26 November 2013}}</ref> When secreted into the [[small intestine]], it mixes with [[enterokinase]] to form active trypsin. Due to its role in the small intestine, trypsin works at an optimal pH of 8.0.<ref>{{cite web |title=Trypsin Product Information|url=http://www.worthington-biochem.com/try/cat.html|work=Worthington Biochemical Corporation|accessdate=26 November 2013}}</ref>
{{Clear}}

==Bacterial assays==
{{Multiple image
|footer= Results of bacterial assays. Left:amylase bacterial assay on a starch medium. A indicates a positive result, D indicates a negative result. Right: lipase bacterial assay on an olive oil medium. 1 shows a positive result, 3 shows a negative result
|width= 200
|image1= Amylase test results.png
|alt1= Amylase test results
|image2= Lipase Assay.png
|alt2= Lipase test results
}}
The production of a particular digestive exoenzyme by a bacterial cell can be assessed using plate [[assay]]s. Bacteria are streaked across the [[agar]], and are left to [[incubator (culture)|incubate]]. The release of the enzyme into the surroundings of the cell cause the breakdown of the [[macromolecule]] on the plate. If a reaction does not occur, this means that the bacteria does not create an exoenzyme capable of interacting with the surroundings. If a reaction does occur, it becomes clear that the bacteria does possess an exoenzyme, and which macromolecule is hydrolyzed determines its identity.<ref name=assays>{{cite web |last=Roberts|first=K|title=Exoenzymes|url=http://academic.pgcc.edu/~kroberts/web/exoenzymes/exoenzymes.htm|publisher=Prince George's Community College|accessdate=8 December 2013|url-status=live|archive-url=https://web.archive.org/web/20130613040514/http://academic.pgcc.edu/~kroberts/web/exoenzymes/exoenzymes.htm|archive-date=13 June 2013}}</ref>

===Amylase===
Amylase breaks down carbohydrates into mono- and disaccharides, so a [[starch]] agar must be used for this assay. Once the bacteria is streaked on the agar, the plate is flooded with [[iodine]]. Since iodine binds to starch but not its digested [[by-product]]s, a clear area will appear where the amylase reaction has occurred. ''[[Bacillus subtilis]]'' is a bacterium that results in a positive assay as shown in the picture.<ref name=assays/>

===Lipase===
Lipase assays are done using a [[lipid]] agar with a [[spirit blue]] dye. If the bacteria has lipase, a clear streak will form in the agar, and the dye will fill the gap, creating a dark blue halo around the cleared area. ''[[Staphylococcus epidermidis]]'' results in a positive lipase assay.<ref name=assays/>
{{Clear}}

==Biotechnological and industrial applications==
[[Microbiological]] sources of exoenzymes including [[amylase]]s, [[protease]]s, pectinases, [[lipase]]s, xylanases, and [[cellulase]]s are used for a wide range of [[biotechnological]] and [[Manufacturing|industrial]] uses including [[biofuel]] generation, [[food]] production, paper manufacturing, [[detergent]]s and [[textile]] production.<ref name=geobiology/> Optimizing the production of [[biofuel]]s has been a focus of researchers in recent years and is centered around the use of [[microorganism]]s 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]].<ref name=biofuel>{{cite journal |vauthors= Alper H, Stephanopoulos G |title= Engineering for biofuels: exploiting innate microbial capacity or importing biosynthetic potential? |journal= Nature Reviews. Microbiology |volume= 7 |issue= 10 |pages= 715–23 |date= October 2009 |pmid= 19756010 |doi= 10.1038/nrmicro2186|s2cid= 7785046 }}</ref> One model of biofuel production is the use of a mixed population of [[bacterial]] [[strain (biology)|strain]]s or a [[consortium]] that work to facilitate the breakdown of [[cellulose]] materials into ethanol by secreting exoenzymes such as cellulases and laccases.<ref name=biofuel/> 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]]. These applications include the breakdown of agricultural and forestry wastes, working as a feed additive to facilitate greater nutrient uptake by livestock, and as an ingredient in bread making to improve the rise and texture of the bread.<ref>{{cite journal |vauthors= Juturu V, Wu JC |title= Microbial xylanases: engineering, production and industrial applications |journal= Biotechnology Advances |volume= 30 |issue= 6 |pages= 1219–27 |date= 1 November 2012 |pmid= 22138412 |doi= 10.1016/j.biotechadv.2011.11.006}}</ref>

[[File:Generic Biodiesel Reaction1.gif|thumb|left|top|upright=1.75|Generic Biodiesel Reaction. Lipases can serve as a biocatalyst in this reaction]]
[[Lipase]]s are one of the most used exoenzymes in [[biotechnology]] and [[Manufacturing|industrial]] applications. Lipases make ideal enzymes for these applications because they are highly selective in their activity, they are readily produced and [[secreted]] by [[bacteria]] and [[fungi]], their [[crystal structure]] is well characterized, they do not require [[cofactor (biochemistry)|cofactor]]s for their [[enzymatic]] activity, and they do not [[catalyze]] side reactions.<ref name=lipase>{{cite journal |last=Jaeger|first=Karl-Erich|author2=Thorsten Eggert|title=Lipases for biotechnology|journal=Current Opinion in Biotechnology|year=2002|volume=13|issue=4|pages=390–397|doi=10.1016/s0958-1669(02)00341-5|pmid=12323363}}</ref> The range of uses of lipases encompasses production of biopolymers, generation of cosmetics, use as a herbicide, and as an effective solvent.<ref name=lipase/> However, perhaps the most well known use of lipases in this field is its use in the production of biodiesel fuel. In this role, lipases are used to convert [[vegetable oil]] to [[methyl]]- and other short-chain [[Alcohol (chemistry)|alcohol]] [[ester]]s by a single [[transesterification]] reaction.<ref>{{cite book |vauthors= Fan X, Niehus X, Sandoval G |chapter= Lipases as Biocatalyst for Biodiesel Production |title= Lipases and Phospholipases |series= Methods in Molecular Biology |volume= 861 |pages= 471–83 |year= 2012 |pmid= 22426735 |doi= 10.1007/978-1-61779-600-5_27 |isbn= 978-1-61779-599-2}}</ref>
{{Clear}}

[[Cellulase]]s, hemicellulases and pectinases are different exoenzymes that are involved in a wide variety of biotechnological and industrial applications. In the [[food industry]] these exoenzymes are used in the production of [[fruit juice]]s, fruit nectars, fruit purees and in the extraction of [[olive oil]] among many others.<ref name=Cellulases>{{cite journal |last=Bhat|first=M.K.|title=Cellulases and related enzymes in biotechnology|journal=Biotechnology Advances|year=2000|volume=18|issue=5|pages=355–383|doi=10.1016/s0734-9750(00)00041-0|pmid=14538100|citeseerx=10.1.1.461.2075}}</ref> The role these enzymes play in these food applications is to partially breakdown the [[plant cell wall]]s and [[pectin]]. In addition to the role they play in [[food production]], cellulases are used in the [[textile industry]] to remove excess [[dye]] from [[denim]], soften [[cotton]] [[fabric]]s, and restore the color brightness of cotton fabrics.<ref name=Cellulases/> Cellulases and hemicellulases (including xylanases) are also used in the [[paper]] and pulp industry to de-ink [[recycled]] [[fiber]]s, modify coarse mechanical pulp, and for the partial or complete [[hydrolysis]] of pulp fibers.<ref name=Cellulases/> Cellulases and hemicellulases are used in these industrial applications due to their ability to hydrolyze the cellulose and hemicellulose components found in these materials.

==Bioremediation applications==
[[File:Runoff of soil & fertilizer.jpg|thumb|left|Water pollution from runoff of soil and fertilizer]]
[[Bioremediation]] is a process in which [[pollutant]]s or [[contaminant]]s in the environment are removed through the use of [[biological]] [[organism]]s or their products. The removal of these often [[hazardous]] pollutants is mostly carried out by naturally occurring or purposely introduced [[microorganism]]s that are capable of [[chemical decomposition|breaking down]] or absorbing the desired pollutant. The types of pollutants that are often the targets of bioremediation strategies are [[petroleum]] products (including oil and [[solvent]]s) and [[pesticide]]s.<ref>{{cite web |title=A Citizen's Guide to Bioremediation|url=https://www.epa.gov/remedytech/citizens-guide-bioremediation|publisher=United States Environmental Protection Agency|accessdate=5 December 2013|date=September 2012}}</ref> In addition to the microorganisms ability to digest and absorb the pollutants, their secreted exoenzymes play an important role in many bioremediation strategies.<ref>{{cite journal |vauthors= Karigar CS, Rao SS |title= Role of microbial enzymes in the bioremediation of pollutants: a review |journal= Enzyme Research |volume= 2011 |pages= 1–11 |year= 2011 |pmid= 21912739 |doi= 10.4061/2011/805187 |pmc=3168789 |doi-access= free }}</ref>

[[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 hydrocarbon]]s (PAHs), [[pesticide]]s, [[synthetic dye]]s, [[chlorophenol]]s, [[explosive]]s, [[crude oil]], and many others.<ref name=fungi>{{cite journal |vauthors= Harms H, Schlosser D, Wick LY |title= Untapped potential: exploiting fungi in bioremediation of hazardous chemicals |journal= Nature Reviews. Microbiology |volume= 9 |issue= 3 |pages= 177–92 |date= March 2011 |pmid= 21297669 |doi= 10.1038/nrmicro2519|s2cid= 24676340 }}</ref> While fungi can breakdown many of these contaminants [[intracellular]]ly, they also secrete numerous [[oxidative]] exoenzymes that work [[extracellular]]ly. One critical aspect of fungi in regards to bioremediation is that they secrete these oxidative exoenzymes from their ever elongating [[hyphal]] tips.<ref name=fungi/> [[Laccase]]s are an important oxidative enzyme that fungi secrete and use [[oxygen]] to [[oxidize]] many pollutants. Some of the pollutants that laccases have been used to treat include dye-containing [[effluent]]s from the textile industry, [[wastewater]] pollutants (chlorophenols, PAHs, etc.), and [[sulfur]]-containing compounds from [[coal]] processing.<ref name=fungi/>
[[File:A simplified model for myosin V (MyoE) function at the hyphal tip in Aspergillus nidulans - journal.pone.0031218.g009A.png|thumb|Exocytic vesicles move along actin microfilaments toward the fungal hyphal tip where they release their contents including exoenzymes]]
[[Bacteria]] are also a viable source of exoenzymes capable of facilitating the bioremediation of the environment. There are many examples of the use of bacteria for this purpose and their exoenzymes encompass many different classes of bacterial enzymes. Of particular interest in this field are bacterial [[hydrolase]]s as they have an [[Intensive and extensive properties|intrinsic]] low [[substrate (chemistry)|substrate]] specificity and can be used for numerous pollutants including solid wastes.<ref name=bacteria>{{cite journal |last=Gianfreda|first=Liliana|author2=Rao, Maria A|title=Potential of extra cellular enzymes in remediation of polluted soils: a review|journal=Enzyme and Microbial Technology|date=September 2004|volume=35|issue=4|pages=339–354|doi=10.1016/j.enzmictec.2004.05.006}}</ref> [[Plastic]] wastes including [[polyurethane]]s are particularly hard to degrade, but an exoenzyme has been identified in a [[Gram-negative]] bacterium, ''Comamonas acidovorans'', that was capable of degrading polyurethane waste in the environment.<ref name=bacteria/> 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.<ref name=bacteria/> In addition to terrestrial based microorganisms, marine based bacteria and their exoenzymes show potential as [[candidate]]s in the field of bioremediation. Marine based bacteria have been utilized in the removal of [[heavy metals]], petroleum/[[diesel fuel|diesel]] degradation and in the removal of polyaromatic hydrocarbons among others.<ref>{{cite journal |vauthors= Dash HR, Mangwani N, Chakraborty J, Kumari S, Das S |title= Marine bacteria: potential candidates for enhanced bioremediation |journal= Applied Microbiology and Biotechnology |volume= 97 |issue= 2 |pages= 561–71 |date= Jan 2013 |pmid= 23212672 |doi= 10.1007/s00253-012-4584-0|s2cid= 253773148 }}</ref>
{{Clear}}

==References==
{{Reflist|33em}}

[[Category:Enzymes]]