ENZYME entry: EC 4.6.1.23

Accepted Name

ribotoxin

Alternative Name(s)

alpha-sarcin

rRNA endonuclease

Reaction catalysed

a 28S rRNA containing guanosine-adenosine pair + H2O = an [RNA fragment]-3'-adenosine-3'-phosphate + a 5'-a hydroxy-guanosine-3'-[RNA fragment]

Comment(s)

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.
Formerly EC 3.1.27.10.

Cross-references

BRENDA

EC2PDB

ExplorEnz

KEGG Ligand Database for Enzyme Nomenclature

IUBMB Enzyme Nomenclature

MEDLINE

MetaCyc

Rhea expert-curated reactions

UniProtKB/Swiss-Prot

C0HLG3, RNAG_CYCAE

P00655, RNAS_ASPGI

All UniProtKB/Swiss-Prot entries referenced in this entry, with possibility to download in different formats, align etc.

All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 4.6.1.-
All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 4.6.-.-
All ENZYME / UniProtKB/Swiss-Prot entries corresponding to 4.-.-.-