葉緑体におけるピリミジンヌクレオチドの生合成

The localization of de novo and salvage pyrimidine biosynthetic pathways in plastids from radish(Raphanus sativus) cotyledons was investigated. The carbamoylphosphate synthetase(EC 6.3.5.5) and aspartate carbamoyltransferase(EC 2.1.3.2), the first two enzymes of the de novo pathway were detected in etioplasts. Uracil phosphoribosyl transferase(EC 2.4.2.9) and uridine kinase(EC 2.7.1.48), the enzymes involved in the salvage pathway of UMP synthesis, were also demonstrated in isolated chloroplasts. We summarized the concentrations of the substrates for these enzymes in chloroplast stroma. From these and previous results(Plant Physiol.80, 126-129, 1986), we concluded that the de novo as well as salvage pathways for pyrimidine biosynthesis operate properly in plastids.