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The Molecular Configuration of Pyrimidines That Causes Allosteric Activation of Uracil Transport in Hymenolepis diminuta
Austin J. MacInnis and Robert K. Ridley
The Journal of Parasitology
Vol. 55, No. 6 (Dec., 1969), pp. 1134-1140
Stable URL: http://www.jstor.org/stable/3277244
Page Count: 7
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A plot of the uptake rate of thymine by H. diminuta was sigmoidal, indicating an allosteric activation of the transport rate. Thymine also stimulated the uptake of uracil, and a Hill plot of these data had a slope of 1.2, suggesting that there are at least 2 binding sites on the purine-pyrimidine permease. From the effects of various pyrimidine analogs on uracil transport, it was concluded that the addition of a methyl group on carbon 5 of uracil gave a structure that caused more activation than 5-amino or 5-bromo groups; when the methyl group was on carbon 6 of uracil, the structure caused inhibition of uracil transport. No effect on uracil transport was observed in the presence of 5-hydroxymethyluracil or 5-carboxyuracil. A plot of the uptake rate of uridine gave typical saturation kinetics, but the presence of thymine stimulated uridine transport. Attempts to show exchange of uracil for other base analogs were negative. Activation of pyrimidine transport by thymine may provide a way to increase permeability of analogs that are effective inhibitors of nucleic acid synthesis.
The Journal of Parasitology © 1969 The American Society of Parasitologists