Editing Β-Galactosidase (section)

== Function  ==
β-Galactosidase is an [[exoglycosidase]] which hydrolyzes the β-[[glycosidic bond]] formed between a [[galactose]] and its organic moiety. It may also cleave [[fucose|fucosides]] and [[Arabinose|arabinosides]] but at a much lower rate.  It is an essential enzyme in the human body. Deficiencies in the protein can result in [[galactosialidosis]] or [[Morquio B syndrome]].  In ''[[Escherichia coli|E. coli]]'', the ''lacZ'' gene is the structural gene for β-galactosidase; which is present as part of the inducible system [[lac operon|''lac'' operon]] which is activated in the presence of [[lactose]] when [[glucose]] level is low. β-Galactosidase synthesis stops when glucose levels are sufficient.<ref>{{Cite book|title=Biochemistry|last=Garrett|first=Reginald | name-list-style = vanc |publisher=Cengage Learning|year=2013|isbn=978-1133106296|location=Belmont, CA|pages=1001}}</ref>

β-Galactosidase has many [[Homologous series|homologues]] based on similar sequences. A few are evolved β-galactosidase (EBG), [[beta-glucosidase|β-glucosidase]], 6-phospho-β-galactosidase, β-mannosidase, and lactase-phlorizin hydrolase. Although they may be structurally similar, they all have different functions.<ref name="IPR017736">{{Cite web| title=Glycoside hydrolase, family 1, β-glucosidase (IPR017736) < InterPro < EMBL-EBI| url=http://www.ebi.ac.uk/interpro/entry/IPR017736| website=www.ebi.ac.uk| access-date=2015-12-11}}</ref> Beta-gal is inhibited by [[Ribose|<small>L</small>-ribose]] and by [[Competitive inhibition|competitive inhibitors]] 2-phenylethyl 1-thio-β-<small>D</small>-galactopyranoside (PETG), <small>D</small>-galactonolactone, [[Isopropyl β-D-1-thiogalactopyranoside|isopropyl thio-β-<small>D</small>-galactoside (IPTG)]], and galactose.<ref name="Juers_2003">{{cite journal | vauthors = Juers DH, Hakda S, Matthews BW, Huber RE | title = Structural basis for the altered activity of Gly794 variants of ''Escherichia coli'' β-galactosidase | journal = Biochemistry | volume = 42 | issue = 46 | pages = 13505–11 | date = November 2003 | pmid = 14621996 | doi = 10.1021/bi035506j }}</ref>

β-Galactosidase is important for organisms as it is a key provider in the production of energy and a source of carbons through the break down of lactose to galactose and glucose. It is also important for [[Lactose intolerance|lactose-intolerant]] people as it is responsible for making lactose-free milk and other dairy products. Many adult humans lack the [[lactase]] enzyme, which has the same function as β-galactosidase, so they are not able to properly digest dairy products. β-Galactose is used in such dairy products as yogurt, sour cream, and some cheeses which are treated with the enzyme to break down any lactose before human consumption. In recent years, β-galactosidase has been researched as a potential treatment for lactose intolerance through gene replacement therapy where it could be placed into the human DNA so individuals can break down lactose on their own.<ref>{{cite journal | vauthors = Salehi S, Eckley L, Sawyer GJ, Zhang X, Dong X, Freund JN, Fabre JW | title = Intestinal lactase as an autologous β-galactosidase reporter gene for in vivo gene expression studies | journal = Human Gene Therapy | volume = 20 | issue = 1 | pages = 21–30 | date = January 2009 | pmid = 20377368 | doi = 10.1089/hum.2008.101 }}</ref><ref>{{cite journal | vauthors = Ishikawa K, Kataoka M, Yanamoto T, Nakabayashi M, Watanabe M, Ishihara S, Yamaguchi S | title = Crystal structure of β-galactosidase from ''Bacillus circulans'' ATCC 31382 (BgaD) and the construction of the thermophilic mutants | journal = The FEBS Journal | volume = 282 | issue = 13 | pages = 2540–52 | date = July 2015 | pmid = 25879162 | doi = 10.1111/febs.13298 | s2cid = 33928719 | doi-access = free }}</ref>