N6-(Δ2-isopentenyl)adenosine: hydrolysis by a nucleosidase isolated from Lactobacillus acidophilus cells

Abstract

A nucleosidase activity has been isolated from Lactobacillus acidophilus which rapidly hydrolyses N6-(Δ2-isopentenyl)adenosine to its corresponding base, N6-(Δ2-isopentenyl)adenine. The activity can be distinguished from the spleen exzyme (EC. 2.4.2.1), a purine nucleoside transferase, on the basis of its substrate specificity, electrophoretic behavior, and non-dependence on phosphate. The bacterial enzyme hydrolyzes both inosine and isopentenyl adenosine, giving Km values of 63.3 μM and 177 μM respectively. The presence of this enzyme in bacteria accounts for the rapid conversion of the parent nucleoside to isopentenyl adenine, which has been observed in these cells. The enzyme thus assumes importance as one of the catabolic activities available to the cell for metabolizing the cytokinin, N6-(Δ2-isopentenyl)adenosine.