Uptake of uridine by a long-day duckweed, Lemna gibba G3

Abstract

Uptake of uridine by a long-day duckweed, Lemna gibba G3 was examined. Km and Vmax for uptake were in the range of 1 to 2 ×10−5 M and of 5 to 10 ×10−8 moles/g fresh weight/2 hr, respectively. Uptake rate depended on temperature, and the optimum pH was 5.0. Uridine uptake was competitively inhibited by some compounds structurally analogous to uridine. However, the activity of uridine kinase was not affected by these compounds, except for cytidine. Uridine uptake was inhibited by metabolic inhibitors, in which uridine taken up was left unconverted to other forms, especially in the presence of DNP. These results suggest that uridine was taken up into the duckweed celb by a specific transport system and immediately phosphorylated by uridine kinase. Phosphorylation of uridine was not associated with the uridine transport reaction.