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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
DOI: 10.2307/3277244
Stable URL: http://www.jstor.org/stable/3277244
Page Count: 7
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Molecular Configuration of Pyrimidines That Causes Allosteric Activation of Uracil Transport in Hymenolepis diminuta
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Abstract

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.

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