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::(S)-hydroxynitrile lyase

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{{#invoke:Infobox|infobox}} (S)-hydroxynitrile lyase (EC 4.1.2.47, (S)-cyanohydrin producing hydroxynitrile lyase, (S)-oxynitrilase, (S)-HbHNL, (S)-MeHNL, hydroxynitrile lyase, oxynitrilase, HbHNL, MeHNL, (S)-selective hydroxynitrile lyase, (S)-cyanohydrin carbonyl-lyase (cyanide forming), hydroxynitrilase) is an enzyme with system name (S)-cyanohydrin lyase (cyanide forming).<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> This enzyme catalyses the following chemical reaction

(1) an aliphatic (S)-hydroxynitrile <math>\rightleftharpoons</math> cyanide + an aliphatic aldehyde or ketone
(2) an aromatic (S)-hydroxynitrile <math>\rightleftharpoons</math> cyanide + an aromatic aldehyde

In nature, the liberation of cyanide serves as a defense mechanism against herbivores and microbial attack in plants.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Hydroxynitrile lyases of the alpha/beta hydrolase fold are closely related to esterases. All members of the alpha/beta hydrolase fold contain a conserved catalytic triad (nucleophile-histidine-aspartate).<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> The nucleophile in this case is a serine. In contrast to esterases, serine proteases, lipases and other enzymes in this family, the nucleophile in hydroxynitrile lyases functions as a proton acceptor. <ref name= >{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Key amino acid residues in this reaction are the lysine at position 236 and the threonine at position 11.<ref name="PUB00004958">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Lys236 helps to orient the substrate while Thr11 serves to block the oxyanion hole that would convert the enzyme into an esterase.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Commonly studied (S)-selective hydroxynitrile lyases include MeHNL from Manihot esculenta and HbHNL from Hevea brasiliensis. (R)-selective hydroxynitrile lyases have also been found to exist in Arabidopsis thaliana (AtHNL). AtHNL is thought to catalyze this reaction by a different mechanism.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Not all hydroxynitrile lyases belong to the alpha/beta hydrolase family. PaHNL (Prunus amygdalus), (R)-selective like AtHNL, uses a flavin cofactor to catalyze cyanogenesis.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>


(S)-hydroxynitrile lyase sections
Intro   Natural Substrates of Hydroxynitrile Lyases    Unnatural Substrates    References    External links   

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Journal::pages    Author::volume    Title::lyase    Issue::enzyme    Lyases::cyanide    Gruber::kratky

{{#invoke:Infobox|infobox}} (S)-hydroxynitrile lyase (EC 4.1.2.47, (S)-cyanohydrin producing hydroxynitrile lyase, (S)-oxynitrilase, (S)-HbHNL, (S)-MeHNL, hydroxynitrile lyase, oxynitrilase, HbHNL, MeHNL, (S)-selective hydroxynitrile lyase, (S)-cyanohydrin carbonyl-lyase (cyanide forming), hydroxynitrilase) is an enzyme with system name (S)-cyanohydrin lyase (cyanide forming).<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref><ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> This enzyme catalyses the following chemical reaction

(1) an aliphatic (S)-hydroxynitrile <math>\rightleftharpoons</math> cyanide + an aliphatic aldehyde or ketone
(2) an aromatic (S)-hydroxynitrile <math>\rightleftharpoons</math> cyanide + an aromatic aldehyde

In nature, the liberation of cyanide serves as a defense mechanism against herbivores and microbial attack in plants.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Hydroxynitrile lyases of the alpha/beta hydrolase fold are closely related to esterases. All members of the alpha/beta hydrolase fold contain a conserved catalytic triad (nucleophile-histidine-aspartate).<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> The nucleophile in this case is a serine. In contrast to esterases, serine proteases, lipases and other enzymes in this family, the nucleophile in hydroxynitrile lyases functions as a proton acceptor. <ref name= >{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Key amino acid residues in this reaction are the lysine at position 236 and the threonine at position 11.<ref name="PUB00004958">{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref> Lys236 helps to orient the substrate while Thr11 serves to block the oxyanion hole that would convert the enzyme into an esterase.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Commonly studied (S)-selective hydroxynitrile lyases include MeHNL from Manihot esculenta and HbHNL from Hevea brasiliensis. (R)-selective hydroxynitrile lyases have also been found to exist in Arabidopsis thaliana (AtHNL). AtHNL is thought to catalyze this reaction by a different mechanism.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>

Not all hydroxynitrile lyases belong to the alpha/beta hydrolase family. PaHNL (Prunus amygdalus), (R)-selective like AtHNL, uses a flavin cofactor to catalyze cyanogenesis.<ref>{{#invoke:Citation/CS1|citation |CitationClass=journal }}</ref>


(S)-hydroxynitrile lyase sections
Intro   Natural Substrates of Hydroxynitrile Lyases    Unnatural Substrates    References    External links   

PREVIOUS: IntroNEXT: Natural Substrates of Hydroxynitrile Lyases
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