N6-(DELTA2-ISOPENTENYL) ADENOSINE . BIOSYNTHESIS IN TRANSFER RIBONUCLEIC ACID IN VITRO

Several molecular species of transfer ribonucleic acid contain an N6-(∆2-isopentenyl)adenosine residue adjacent to the 3′ end of the anticodon. The biosynthesis of this component has been investigated. Yeast and rat liver contain an enzyme that catalyzes in vitro the transfer of the ∆2-isopentenyl group from ∆2-isopentenyl pyrophosphate to a receptor adenosine residue in homologous suitably treated transfer ribonucleic acid resulting in the synthesis of the N6-(∆2-isopentenyl)adenosine component of transfer ribonucleic acid. The enzyme has been purified 50-100-fold from yeast. ∆3-isopentenyl pyrophosphate is not a substrate. The enzyme does not catalyze the attachment of the isopentenyl group to the native transfer ribonucleic acid but does catalyze the reaction with permanganate-treated transfer ribonucleic acid. The permanganate treatment is specific for cleavage of the ∆2-isopentenyl groups of transfer ribonucleic acid leaving adenosine residues. Therefore, a specific adenosine residue in the transfer ribonucleic acid serves as the receptor site of the ∆2-isopentenyl group. Support for this conclusion comes from an experiment in which the N6-(∆2-isopentenyl)adenosine residues are rendered insensitive to permanganate oxidation. The transfer ribonucleic acid is treated with iodine which reacts specifically with the N6-(∆2-isopentenyl)adenosine residues and prevents further reaction with permanganate. Transfer ribonucleic acid treated first with iodine and then with permanganate does not serve as a substrate. The enzyme systems from both yeast and rat liver catalyze a significant incorporation of ∆2-isopentenyl groups into untreated transfer ribonucleic acid from Escherichia coli B. © 1969, American Chemical Society. All rights reserved.