chitinase

Chitinivorous organisms include many bacteria{{cite journal | vauthors = Xiao X, Yin X, Lin J, Sun L, You Z, Wang P, Wang F | title = Chitinase genes in lake sediments of Ardley Island, Antarctica | journal = Applied and Environmental Microbiology | volume = 71 | issue = 12 | pages = 7904–9 | date = December 2005 | pmid = 16332766 | pmc = 1317360 | doi = 10.1128/AEM.71.12.7904-7909.2005 | bibcode = 2005ApEnM..71.7904X }} (Aeromonads, Bacillus, Vibrio,{{cite journal | vauthors = Hunt DE, Gevers D, Vahora NM, Polz MF | title = Conservation of the chitin utilization pathway in the Vibrionaceae | journal = Applied and Environmental Microbiology | volume = 74 | issue = 1 | pages = 44–51 | date = January 2008 | pmid = 17933912 | pmc = 2223224 | doi = 10.1128/AEM.01412-07 | bibcode = 2008ApEnM..74...44H }} among others), which may be pathogenic or detritivorous. They attack living arthropods, zooplankton or fungi or they may degrade the remains of these organisms.

Fungi, such as Coccidioides immitis, also possess degradative chitinases related to their role as detritivores and also to their potential as arthropod pathogens.

Chitinases are also present in plants – for example barley seed chitinase: {{PDB|1CNS}}, {{EC number|3.2.1.14}}. Barley seeds are found to produce clone 10 in Ignatius et al 1994(a). They find clone 10, a Class I chitinase, in the seed aleurone during development.{{cite journal | vauthors = Muthukrishnan S, Liang GH, Trick HN, Gill BS | journal=Plant Cell, Tissue and Organ Culture | publisher=Kluwer Academic | volume=64 | issue=2/3 | year=2001 | issn=0167-6857 | doi=10.1023/a:1010763506802 | pages=93–114 | title=Pathogenesis-related proteins and their genes in cereals| s2cid=43466565 }}{{cite journal | vauthors = Gomez L, Allona I, Casado R, Aragoncillo C | title=Seed chitinases | journal=Seed Science Research | publisher=Cambridge University Press (CUP) | volume=12 | issue=4 | year=2002 | issn=0960-2585 | doi=10.1079/ssr2002113 | pages=217–230| s2cid=233361411 }}{{cite journal | vauthors = Waniska RD, Venkatesha RT, Chandrashekar A, Krishnaveni S, Bejosano FP, Jeoung J, Jayaraj J, Muthukrishnan S, Liang GH | display-authors = 6 | title = Antifungal proteins and other mechanisms in the control of sorghum stalk rot and grain mold | journal = Journal of Agricultural and Food Chemistry | volume = 49 | issue = 10 | pages = 4732–4742 | date = October 2001 | pmid = 11600015 | doi = 10.1021/jf010007f | publisher = American Chemical Society (ACS) }} Leaves produce several isozymes (as well as several of β-1,3-glucanase). Ignatius et al 1994(b) find these in the leaves, induced by powdery mildew. Ignatius et al also find these (seed and leaf isozymes) to differ from each other.{{cite book | first= A.S. |last=Basra | title=Handbook of Seed Science and Technology | publisher=Scientific Publishers | year=2007 | isbn=978-93-88148-36-8 | url=https://books.google.com/books?id=mNaBDwAAQBAJ | access-date=2021-11-17 | pages=795 |doi=10.2307/25065722 |jstor=25065722 | section=3. Seed Ecology Chapter 16. Natural defense mechanisms in seeds | s2cid=83869430}} {{ISBN|9788172335731}} {{ISBN|9388148363}}. Some of these are pathogenesis related (PR) proteins that are induced as part of systemic acquired resistance. Expression is mediated by the NPR1 gene and the salicylic acid pathway, both involved in resistance to fungal and insect attack. Other plant chitinases may be required for creating fungal symbioses.{{cite journal | vauthors = Salzer P, Bonanomi A, Beyer K, Vögeli-Lange R, Aeschbacher RA, Lange J, Wiemken A, Kim D, Cook DR, Boller T | display-authors = 6 | title = Differential expression of eight chitinase genes in Medicago truncatula roots during mycorrhiza formation, nodulation, and pathogen infection | journal = Molecular Plant-Microbe Interactions | volume = 13 | issue = 7 | pages = 763–777 | date = July 2000 | pmid = 10875337 | doi = 10.1094/MPMI.2000.13.7.763 | doi-access = free }}

Although mammals do not produce chitin, they have two functional chitinases, Chitotriosidase (CHIT1) and acidic mammalian chitinase (AMCase), as well as chitinase-like proteins (such as YKL-40) that have high sequence similarity but lack chitinase activity.{{cite journal | vauthors = Eurich K, Segawa M, Toei-Shimizu S, Mizoguchi E | title = Potential role of chitinase 3-like-1 in inflammation-associated carcinogenic changes of epithelial cells | journal = World Journal of Gastroenterology | volume = 15 | issue = 42 | pages = 5249–59 | date = November 2009 | pmid = 19908331 | pmc = 2776850 | doi = 10.3748/wjg.15.5249 | doi-access = free }}

1. Endochitinases (EC 3.2.1.14) randomly split chitin at internal sites of the chitin microfibril, forming soluble, low molecular mass multimer products. The multimer products includes di-acetylchitobiose, chitotriose, and chitotetraose, with the dimer being the predominant product.{{cite journal | vauthors= Sahai AS, Manocha MS |date=1993-08-01|title=Chitinases of fungi and plants: their involvement in morphogenesis and host—parasite interaction | journal=FEMS Microbiology Reviews | volume = 11 | issue = 4 | pages = 317–338 | doi = 10.1111/j.1574-6976.1993.tb00004.x |s2cid=86267956 | doi-access= free }}
2. Exochitinases have also been divided into two sub categories:
3. Chitobiosidases ({{EnzExplorer|3.2.1.29}}) act on the non-reducing end of the chitin microfibril, releasing the dimer, di-acetylchitobiose, one by one from the chitin chain. Therefore, there is no release of monosaccharides or oligosaccharides in this reaction.{{Cite journal | vauthors = Harman GE | title=Chitinolytic Enzymes of Trichoderma harzianum: Purification of Chitobiosidase and Endochitinase | journal=Phytopathology|volume=83|issue=3|pages=313|doi=10.1094/phyto-83-313 | year=1993 }}
4. β-1,4- N-acetylglucosaminidases ({{EnzExplorer|3.2.1.30}}) split the multimer products, such as di-acetylchitobiose, chitotriose, and chitotetraose, into monomers of N-acetylglucoseamine (GlcNAc).

Chitinases were also classified based on the amino acid sequences, as that would be more helpful in understanding the evolutionary relationships of these enzymes to each other.{{cite journal | vauthors = Patil RS, Ghormade V, Deshpande MV | title = Chitinolytic enzymes: an exploration | journal = Enzyme and Microbial Technology | volume = 26 | issue = 7 | pages = 473–483 | date = April 2000 | pmid = 10771049 | doi = 10.1016/s0141-0229(00)00134-4 | name-list-style = vanc }} Therefore, the chitinases were grouped into three families: 18, 19, and 20.{{cite journal | vauthors = Henrissat B | title = A classification of glycosyl hydrolases based on amino acid sequence similarities | journal = The Biochemical Journal | volume = 280 ( Pt 2) | issue = 2 | pages = 309–16 | date = December 1991 | pmid = 1747104 | pmc = 1130547 | doi = 10.1042/bj2800309 }} Both families 18 and 19 consists of endochitinases from a variety of different organisms, including viruses, bacteria, fungi, insect, and plants. However, family 19 mainly comprises plant chitinases. Family 20 includes N-acetylglucosaminidase and a similar enzyme, N-acetylhexosaminidase.

And as the gene sequences of the chitinases were known, they were further classified into six classes based on their sequences. Characteristics that determined the classes of chitinases were the N-terminal sequence, localization of the enzyme, isoelectric pH, signal peptide, and inducers.

{{visible anchor|Class I}} chitinases had a cysteine-rich N-terminal, leucine- or valine-rich signal peptide, and vacuolar localization. And then, Class I chitinases were further subdivided based on their acidic or basic nature into {{visible anchor|Class Ia}} and {{visible anchor|Class Ib}}, respectively.{{Cite journal | vauthors = Flach J, Pilet PE, Jollès P | date = August 1992 | title=What's new in chitinase research? | journal = Experientia | volume=48|issue=8|pages=701–716|doi=10.1007/BF02124285 | pmid = 1516675 | s2cid = 37362071 }} Class 1 chitinases were found to comprise only plant chitinases and mostly endochitinases.

{{visible anchor|Class II}} chitinases did not have the cysteine-rich N-terminal but had a similar sequence to Class I chitinases. Class II chitinases were found in plants, fungi, and bacteria and mostly consisted of exochitinases.

{{visible anchor|Class III}} chitinases did not have similar sequences to chitinases in Class I or Class II.

{{visible anchor|Class IV}} chitinases had similar characteristics, including the immunological properties, as Class I chitinases. However, Class IV chitinases were significantly smaller in size compared to Class I chitinases.{{cite journal | vauthors = Collinge DB, Kragh KM, Mikkelsen JD, Nielsen KK, Rasmussen U, Vad K | title = Plant chitinases | journal = The Plant Journal | volume = 3 | issue = 1 | pages = 31–40 | date = January 1993 | pmid = 8401605 | doi = 10.1046/j.1365-313x.1993.t01-1-00999.x | name-list-style = vanc | doi-access = free }}

{{visible anchor|Class V}} and {{visible anchor|Class VI}} chitinases are not well characterized. However, one example of a Class V chitinase showed two chitin binding domains in tandem, and based on the gene sequence, the cysteine-rich N-terminal seemed to have been lost during evolution, probably due to less selection pressure that caused the catalytic domain to lose its function.File:Endochitinase.pngFile:Exochitinase.png

Like cellulose, chitin is an abundant biopolymer that is relatively resistant to degradation.{{cite journal |journal=Journal of Experimental Zoology |vauthors=Akaki C, Duke GE |year=2005 |volume=283 |issue=4–5 |pages=387–393 |title=Apparent chitin digestibilities in the Eastern screech owl (Otus asio) and the American kestrel (Falco sparverius) |doi=10.1002/(SICI)1097-010X(19990301/01)283:4/5<387::AID-JEZ8>3.0.CO;2-W}} Many mammals can digest chitin and the specific chitinase levels in vertebrate species are adapted to their feeding behaviours.{{cite journal | vauthors = Tabata E, Kashimura A, Kikuchi A, Masuda H, Miyahara R, Hiruma Y, Wakita S, Ohno M, Sakaguchi M, Sugahara Y, Matoska V, Bauer PO, Oyama F | display-authors = 6 | title = Chitin digestibility is dependent on feeding behaviors, which determine acidic chitinase mRNA levels in mammalian and poultry stomachs | journal = Scientific Reports | volume = 8 | issue = 1 | pages = 1461 | date = January 2018 | pmid = 29362395 | pmc = 5780506 | doi = 10.1038/s41598-018-19940-8 | bibcode = 2018NatSR...8.1461T }} Certain fish are able to digest chitin.{{cite journal | vauthors = Gutowska MA, Drazen JC, Robison BH | title = Digestive chitinolytic activity in marine fishes of Monterey Bay, California | journal = Comparative Biochemistry and Physiology. Part A, Molecular & Integrative Physiology | volume = 139 | issue = 3 | pages = 351–8 | date = November 2004 | pmid = 15556391 | doi = 10.1016/j.cbpb.2004.09.020 | citeseerx = 10.1.1.318.6544 }} Chitinases have been isolated from the stomachs of mammals, including humans.{{cite journal | vauthors = Paoletti MG, Norberto L, Damini R, Musumeci S | title = Human gastric juice contains chitinase that can degrade chitin | journal = Annals of Nutrition & Metabolism | volume = 51 | issue = 3 | pages = 244–51 | year = 2007 | pmid = 17587796 | doi = 10.1159/000104144 | s2cid = 24837500 }}

Chitinase activity can also be detected in human blood{{cite journal | vauthors = Renkema GH, Boot RG, Muijsers AO, Donker-Koopman WE, Aerts JM | title = Purification and characterization of human chitotriosidase, a novel member of the chitinase family of proteins | journal = The Journal of Biological Chemistry | volume = 270 | issue = 5 | pages = 2198–202 | date = February 1995 | pmid = 7836450 | doi = 10.1074/jbc.270.5.2198 | doi-access = free | hdl = 1887/50684 | hdl-access = free }}{{cite journal | vauthors = Escott GM, Adams DJ | title = Chitinase activity in human serum and leukocytes | journal = Infection and Immunity | volume = 63 | issue = 12 | pages = 4770–3 | date = December 1995 | doi = 10.1128/IAI.63.12.4770-4773.1995 | pmid = 7591134 | pmc = 173683 | url = }} and possibly cartilage.{{cite journal | vauthors = Hakala BE, White C, Recklies AD | title = Human cartilage gp-39, a major secretory product of articular chondrocytes and synovial cells, is a mammalian member of a chitinase protein family | journal = The Journal of Biological Chemistry | volume = 268 | issue = 34 | pages = 25803–10 | date = December 1993 | doi = 10.1016/S0021-9258(19)74461-5 | pmid = 8245017 | doi-access = free }} As in plant chitinases this may be related to pathogen resistance.{{cite journal | vauthors = Recklies AD, White C, Ling H | title = The chitinase 3-like protein human cartilage glycoprotein 39 (HC-gp39) stimulates proliferation of human connective-tissue cells and activates both extracellular signal-regulated kinase- and protein kinase B-mediated signalling pathways | journal = The Biochemical Journal | volume = 365 | issue = Pt 1 | pages = 119–26 | date = July 2002 | pmid = 12071845 | pmc = 1222662 | doi = 10.1042/BJ20020075 }}{{cite journal | vauthors = van Eijk M, van Roomen CP, Renkema GH, Bussink AP, Andrews L, Blommaart EF, Sugar A, Verhoeven AJ, Boot RG, Aerts JM | title = Characterization of human phagocyte-derived chitotriosidase, a component of innate immunity | journal = International Immunology | volume = 17 | issue = 11 | pages = 1505–12 | date = November 2005 | pmid = 16214810 | doi = 10.1093/intimm/dxh328 | doi-access = free }}

Chitinases production in the human body (known as "human chitinases") may be in response to allergies, and asthma has been linked to enhanced chitinase expression levels.{{cite journal | vauthors = Bierbaum S, Nickel R, Koch A, Lau S, Deichmann KA, Wahn U, Superti-Furga A, Heinzmann A | title = Polymorphisms and haplotypes of acid mammalian chitinase are associated with bronchial asthma | journal = American Journal of Respiratory and Critical Care Medicine | volume = 172 | issue = 12 | pages = 1505–9 | date = December 2005 | pmid = 16179638 | pmc = 2718453 | doi = 10.1164/rccm.200506-890OC }}{{cite journal | vauthors = Zhao J, Zhu H, Wong CH, Leung KY, Wong WS | title = Increased lungkine and chitinase levels in allergic airway inflammation: a proteomics approach | journal = Proteomics | volume = 5 | issue = 11 | pages = 2799–807 | date = July 2005 | pmid = 15996009 | doi = 10.1002/pmic.200401169 | s2cid = 38710491 }}{{cite journal | vauthors = Elias JA, Homer RJ, Hamid Q, Lee CG | title = Chitinases and chitinase-like proteins in T(H)2 inflammation and asthma | journal = The Journal of Allergy and Clinical Immunology | volume = 116 | issue = 3 | pages = 497–500 | date = September 2005 | pmid = 16159614 | doi = 10.1016/j.jaci.2005.06.028 }}{{cite journal | vauthors = Zhu Z, Zheng T, Homer RJ, Kim YK, Chen NY, Cohn L, Hamid Q, Elias JA | title = Acidic mammalian chitinase in asthmatic Th2 inflammation and IL-13 pathway activation | journal = Science | volume = 304 | issue = 5677 | pages = 1678–82 | date = June 2004 | pmid = 15192232 | doi = 10.1126/science.1095336 | bibcode = 2004Sci...304.1678Z | s2cid = 19486575 }}{{cite journal | vauthors = Chupp GL, Lee CG, Jarjour N, Shim YM, Holm CT, He S, Dziura JD, Reed J, Coyle AJ, Kiener P, Cullen M, Grandsaigne M, Dombret MC, Aubier M, Pretolani M, Elias JA | title = A chitinase-like protein in the lung and circulation of patients with severe asthma | journal = The New England Journal of Medicine | volume = 357 | issue = 20 | pages = 2016–27 | date = November 2007 | pmid = 18003958 | doi = 10.1056/NEJMoa073600 | doi-access = free }}

Human chitinases may explain the link between some of the most common allergies (dust mites, mold spores—both of which contain chitin) and worm (helminth) infections, as part of one version of the hygiene hypothesis{{cite journal | vauthors = Maizels RM | title = Infections and allergy - helminths, hygiene and host immune regulation | journal = Current Opinion in Immunology | volume = 17 | issue = 6 | pages = 656–61 | date = December 2005 | pmid = 16202576 | doi = 10.1016/j.coi.2005.09.001 }}{{cite journal | vauthors = Hunter MM, McKay DM | title = Review article: helminths as therapeutic agents for inflammatory bowel disease | journal = Alimentary Pharmacology & Therapeutics | volume = 19 | issue = 2 | pages = 167–77 | date = January 2004 | pmid = 14723608 | doi = 10.1111/j.0269-2813.2004.01803.x | s2cid = 73016367 | doi-access = free }}{{cite journal | vauthors = Palmas C, Gabriele F, Conchedda M, Bortoletti G, Ecca AR | title = Causality or coincidence: may the slow disappearance of helminths be responsible for the imbalances in immune control mechanisms? | journal = Journal of Helminthology | volume = 77 | issue = 2 | pages = 147–53 | date = June 2003 | pmid = 12756068 | doi = 10.1079/JOH2003176 | s2cid = 24555145 }} (worms have chitinous mouthparts to hold the intestinal wall). Finally, the link between chitinases and salicylic acid in plants is well established{{explain|reason=What is the content of this link? What does it explain?|date=December 2015}}—but there is a hypothetical link between salicylic acid and allergies in humans.{{cite journal | vauthors = Feingold BF | title = Food additives in clinical medicine | journal = International Journal of Dermatology | volume = 14 | issue = 2 | pages = 112–4 | date = March 1975 | pmid = 1123257 | doi = 10.1111/j.1365-4362.1975.tb01426.x | s2cid = 73187904 }}{{non sequitur|date=August 2021}}

May be used to monitor enzymotherapy supplementation in Gaucher's disease.[https://www.em-consulte.com/article/47075/gaucher-disease-and-chitotriosidase]

Regulation varies from species to species, and within an organism, chitinases with different physiological functions would be under different regulation mechanisms. For example, chitinases that are involved in maintenance, such as remodeling the cell wall, are constitutively expressed. However, chitinases that have specialized functions, such as degrading exogenous chitin or participating in cell division, need spatio-temporal regulation of the chitinase activity.{{cite journal | vauthors = Langner T, Göhre V | title = Fungal chitinases: function, regulation, and potential roles in plant/pathogen interactions | journal = Current Genetics | volume = 62 | issue = 2 | pages = 243–54 | date = May 2016 | pmid = 26527115 | doi = 10.1007/s00294-015-0530-x | s2cid = 10360301 }}

The regulation of an endochitinase in Trichoderma atroviride is dependent on a N-acetylglucosaminidase, and the data indicates a feedback-loop where the break down of chitin produces N-acetylglucosamine, which would be possibly taken up and triggers up-regulation of the chitinbiosidases.{{cite journal | vauthors = Brunner K, Peterbauer CK, Mach RL, Lorito M, Zeilinger S, Kubicek CP | title = The Nag1 N-acetylglucosaminidase of Trichoderma atroviride is essential for chitinase induction by chitin and of major relevance to biocontrol | journal = Current Genetics | volume = 43 | issue = 4 | pages = 289–95 | date = July 2003 | pmid = 12748812 | doi = 10.1007/s00294-003-0399-y | s2cid = 22135834 }}

In Saccharomyces cerevisiae and the regulation of ScCts1p (S. cerevisiae chitinase 1), one of the chitinases involved in cell separation after cytokinesis by degrading the chitin of the primary septum.{{cite journal | vauthors = Kuranda MJ, Robbins PW | title = Chitinase is required for cell separation during growth of Saccharomyces cerevisiae | journal = The Journal of Biological Chemistry | volume = 266 | issue = 29 | pages = 19758–67 | date = October 1991 | doi = 10.1016/S0021-9258(18)55057-2 | pmid = 1918080 | doi-access = free }} As these types of chitinases are important in cell division, there must be tight regulation and activation. Specifically, Cts1 expression has to be activated in daughter cells during late mitosis and the protein has to localize at the daughter site of the septum.{{cite journal | vauthors = Colman-Lerner A, Chin TE, Brent R | title = Yeast Cbk1 and Mob2 activate daughter-specific genetic programs to induce asymmetric cell fates | journal = Cell | volume = 107 | issue = 6 | pages = 739–50 | date = December 2001 | pmid = 11747810 | doi = 10.1016/S0092-8674(01)00596-7 | s2cid = 903530 | doi-access = free }} And to do this, there must be coordination with other networks controlling the different phases of the cell, such as Cdc14 Early Anaphase Release (FEAR), mitotic exit network (MEN), and regulation of Ace2p (transcription factor) and cellular morphogenesis (RAM){{cite journal | vauthors = Nelson B, Kurischko C, Horecka J, Mody M, Nair P, Pratt L, Zougman A, McBroom LD, Hughes TR, Boone C, Luca FC | title = RAM: a conserved signaling network that regulates Ace2p transcriptional activity and polarized morphogenesis | journal = Molecular Biology of the Cell | volume = 14 | issue = 9 | pages = 3782–803 | date = September 2003 | pmid = 12972564 | doi = 10.1091/mbc.E03-01-0018 | pmc = 196567 }} signalling networks. Overall, the integration of the different regulatory networks allows for the cell wall degrading chitinase to function dependent on the cell's stage in the cell cycle and at specific locations among the daughter cells.

Chitinases occur naturally in many common foods. Phaseolus vulgaris, bananas, chestnuts, kiwifruit, avocados, papaya, and tomatoes, for example, all contain significant levels of chitinase, as defense against fungal and invertebrate attack. Stress, or environmental signals like ethylene gas, may stimulate increased production of chitinase.

Some parts of chitinase molecules, almost identical in structure to hevein or other proteins in rubber latex due to their similar function in plant defense, may trigger an allergic cross-reaction known as latex-fruit syndrome.{{cite web | title = Latex-Fruit Syndrome and Class 2 Food Allergy | url = http://dmd.nihs.go.jp/latex/cross-e.html | work = Division of Medical Devices, Japan | access-date = 2017-02-16 | archive-date = 2020-11-11 | archive-url = https://web.archive.org/web/20201111201836/http://dmd.nihs.go.jp/latex/cross-e.html | url-status = dead }}

Chitinases have a wealth of applications, some of which have already been realized by industry. This includes bio-conversion of chitin to useful products such as fertilizer, the production of non-allergenic, non-toxic, biocompatible, and biodegradable materials (contact lenses, artificial skin and sutures with these qualities are already being produced) and enhancement of insecticides and fungicides.{{cite journal | vauthors = Hamid R, Khan MA, Ahmad M, Ahmad MM, Abdin MZ, Musarrat J, Javed S | title = Chitinases: An update | journal = Journal of Pharmacy & Bioallied Sciences | volume = 5 | issue = 1 | pages = 21–9 | date = January 2013 | pmid = 23559820 | pmc = 3612335 | doi = 10.4103/0975-7406.106559 | doi-access = free }} Phaseolus vulgaris chitinase - bean chitinase, BCH - has been transgenically inserted as a pest deterrent into entirely unrelated crops.

Possible future applications of chitinases are as food additives to increase shelf life, therapeutic agent for asthma and chronic rhinosinusitis, as an anti-fungal remedy, an anti-tumor drug and as a general ingredient to be used in protein engineering.

• Ligninase

{{Reflist|refs=

{{cite journal | title=Transgenic potato plants with enhanced resistance to the tomato moth, Lacanobia oleracea: growth room trials | s2cid=23765916 | vauthors = Gatehouse AM, Davison GM, Newell CA, Merryweather A, Hamilton WD, Burgess EP, Gilbert RJ, Gatehouse JA | display-authors = 6 | journal=Molecular Breeding | publisher=Springer Science+Business | volume=3 | issue=1 | year=1997 | issn=1380-3743 | doi=10.1023/a:1009600321838 | pages=49–63}}

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• {{MeshName|Chitinase}}
• [https://web.archive.org/web/20080303025351/http://www.proteinscience.org/cgi/content/abstract/9/3/544 The X-ray structure of a chitinase from the pathogenic fungus Coccidioides immitis]

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Category:EC 3.2.1

Category:Enzymes