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No Effect of 5-Fluorouracil on the Properties of Purified -Amylase from Barley Half-seeds ¹

Michigan State University Energy Research and Development Administration, Plant Research Laboratory Michigan State University, East Lansing, Michigan 48824

-Amylase has been purified from de-embryonated seeds of barley (Hordeum vulgare L. cv. Betzes) which have been incubated on 10^–6 M gibberellic acid (GA₃) following 3 days of imbibition in buffer. Incubation of the half-seeds in up to 10^–2 M 5-fluorouracil (5-FU) during the entire incubation period, including imbibition, had no effect on any of the following characteristics of purified -amylase: thermal stability in the absence of calcium, molecular weight of the enzyme, isozyme composition, specific activity, or the amount of -amylase synthesized by the aleurone tissue. The synthesis of rRNA and tRNA was strongly inhibited by 5-FU, indicating that the analog had entered the aleurone cells. These results are not in agreement with those of Carlson (Nature New Biology 237: 39-41 [1972]) who found that treatment of barley aleurone with 10^–4 M 5-FU prior to the addition of GA₃ resulted in decreased thermal stability of GA₃-induced -amylase and who interpreted this as evidence that the mRNA for -amylase was synthesized during the imbibition of the aleurone tissue and independently of gibberellin action. Results of the present experiments indicate that the thermal stability of highly purified -amylase is not altered by treatment of barley half-seeds with 5-FU, and that 5-FU cannot be used as a probe to examine the timing of -amylase mRNA synthesis.

¹ This research was supported by United States Energy Research and Development Administration Contract EY-76-C-02-1338 and by National Science Foundation Grant BMS 74-23471.