The enzymic phosphorylation of N6-(delta 2-isopentenyl) adenosine in chick liver homogenates.

Abstract

Enzyme preparations from chick kidney and liver rapidly phosphorylate the modified nucleoside, N6-(Δ2-isopentenyl) adenosine. The resulting metabolite behaves electrophoretically as a mononucleotide and is quantitatively hydrolyzed to the nucleoside by 5′-nucleotidase. The isopentenyl side chain is not altered in the phosphorylated derivative. It is concluded that the metabolite is N6-(Δ2-isopentenyl) adenosine-5′-monophosphate. The properties of the enzyme activity responsible for the phosphorylation resemble the properties of adenosine kinase isolated from sarcoma-180 cells, and from rabbit liver, with respect to pH optimum, Km value, and sensitivity to magnesium ion and ATP. Thus, it seems probable that the phosphorylation observed in the chick tissue preparations is due to adenosine kinase. The mononucleotide could not be further phosphorylated in vitro by adenylate kinase. This observation, coupled with the fact that isopentenyladenosine is biosynthesized at the macromolecular level, suggests that the 5′-monophosphate ester may be the form through which some of the biological effects of this modified nucleoside are manifested.A major end product of N6-(Δ2-isopentenyl) adenosine catabolism in chick liver and kidney homogenates is uric acid.