Papain: Difference between revisions
From Proteopedia
Jump to navigationJump to search
No edit summary |
No edit summary |
||
| Line 46: | Line 46: | ||
===Function=== | ===Function=== | ||
As a cysteine protease, Papain utilizes a nucleophilic cysteine thiol as part of its catalytic triad. Papain's Cys-25 is deprotonated by its His-159. The now nucleophilic Cys-25 attacks the carbonyl carbon of the peptide backbone, forming an acyl enzyme intermediate in which the peptide's amino terminal is free. Also in this step, His-159 is returned to its deprotonated form. The intermediate is then deacylated by a water molecule, and it releases the carboxyl terminal of the peptide to produce the product and regenerate the active enzyme. This entire mechanism is shown below: | As a cysteine protease, Papain utilizes a nucleophilic cysteine thiol as part of its catalytic triad. Papain's Cys-25 is deprotonated by its His-159. The now nucleophilic Cys-25 attacks the carbonyl carbon of the peptide backbone, forming an acyl enzyme intermediate in which the peptide's amino terminal is free. Also in this step, His-159 is returned to its deprotonated form. The intermediate is then deacylated by a water molecule, and it releases the carboxyl terminal of the peptide to produce the product and regenerate the active enzyme. This entire mechanism is shown below: | ||
[[Image:jrip.jpg| | [[Image:jrip.jpg|400px|center|thumb|Papain Mechanism]] | ||
<ref>Image from: | <ref>Image from: | ||
http://upload.wikimedia.org/wikipedia/commons/5/5c/Cysteinprotease_Reaktionsmechanismus.svg</ref>]] | http://upload.wikimedia.org/wikipedia/commons/5/5c/Cysteinprotease_Reaktionsmechanismus.svg</ref>]] | ||
