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ENZYME entry: EC

Accepted Name
Alternative Name(s)
(28S-rRNA)-guanosine-adenosine 5'-hydroxy-guanosine-ribonucleotide- 3'-(RNA fragment)-lyase (cyclicizing; (RNA fragment)-3'-adenosine- 2',3'-cyclophosphate-forming and hydrolyzing).
rRNA endonuclease.
Reaction catalysed
A 28S rRNA containing guanosine-adenosine pair + H(2)O <=> an (RNA fragment)-3'-adenosine-3'-phosphate + a 5'-a hydroxy-guanosine-3'-(RNA fragment)
  • Ribotoxins are rRNA endonucleases that catalyze the cleavage of the phosphodiester bond between guanosine and adenosine residues at one specific position in 28S rRNA.
  • The enzyme secreted by Aspergillus giganteus specifically cleaves rat 28S rRNA between G(4325) and A(4326) and displays cytotoxic activity toward animal cells.
  • It can also act on bacterial rRNAs.
  • The enzyme catalyzes a two-stage endonucleolytic cleavage.
  • The first reaction produces 5'-hydroxy-phosphooligonucletides and 3'-phosphooligonucleotides ending with 2',3'-cyclic phosphodiester, which are released from the enzyme.
  • The enzyme then hydrolyzes these cyclic compounds in a second reaction that takes place only when all the susceptible 3',5'-phosphodiester bonds have been cyclised.
  • The second reaction is a reversal of the first reaction using the hydroxyl group of water instead of the 5'-hydroxyl group of ribose.
  • The overall process is that of a phosphorus-oxygen lyase followed by hydrolysis to form the 3'-nucleotides.
PRIAM enzyme-specific profiles4.6.1.23
KEGG Ligand Database for Enzyme Nomenclature4.6.1.23
IUBMB Enzyme Nomenclature4.6.1.23
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