Subcellular compartmentation of uridine nucleotides and nucleoside-5' -diphosphate kinase in leaves.

The subcellular compartmentation of nucleoside diphosphate kinase (EC 2.7.4.6) and the uridine nucleotides has been studied in leaves. Membrane filtration of barley (Hordeum vulgare L.) leaf mesophyll protoplasts and differential centrifugation of spinach (Spinacia oleracea L.) leaf extracts showed that about half the nucleoside diphosphate kinase is present in the cytosol. The activity is adequate to account for the turnover of UTP and UDP during photosynthetic sucrose synthesis. Nonaqueous density gradient centrifugation of freeze-stopped, lyophilized spinach leaf material showed that the uridine nucleotides are predominantly located in the cytosol and that the cytosolic UDP-glucose pool is considerably larger than the UTP or UDP pools.