Regulation of Pyrimidine and Arginine Biosynthesis Investigated by the Use of Phaseolotoxin and 5-Fluorouracil

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Abstract
Purified phaseolotoxin [prepared from Pseudomonas syringae var. Phaseolicola] inhibits the growth of carrot [Daucus carota] cells. Such inhibitions were reversed completely by citrulline but not by arginine. This toxin inhibits ornithine transcarbamylase activity in vitro, which leads to an accumulation of ornithine and a decrease in arginine levels intracellularly. In carrot cells, 5-fluorouracil (5-FU) toxicity was reduced by the addition of purified toxin and citrulline or ornithine. The toxin decreases the incorporation of [14C]uracil and [14C]5-FU into trichloroacetic acid precipitable material by 50%. A 5-FU-resistant line, F5 (Sung ZR et al.) was more sensitive to the toxin than were 5-FU-sensitive cells. One millimolar 5-FU roughly doubled the ability of F5 to tolerate phaseolotoxin. A close regulation apparently is operative between the pyrimidine and arginine pathways in carrots.