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The influx of purines and pyrimidines across the brush border of Hymenolepis diminuta*

Published online by Cambridge University Press:  06 April 2009

Peter W. Pappas ,
Gary L. Uglem  and
Clark P. Read
Peter W. Pappas
Affiliation:
Department of Biology, Rice University, Houston, Texas 77001
Gary L. Uglem
Affiliation:
Department of Biology, Rice University, Houston, Texas 77001
Clark P. Read
Affiliation:
Department of Biology, Rice University, Houston, Texas 77001
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Extract

The kinetics of uracil, thymine, 5-bromouracil, hypoxanthine, guanine and adenine uptake by Hymenolepis diminuta were studied using shortterm (2 min) incubations. The effects of other purines and pyrimidines on the uptake of these compounds was determined. The data suggest that the purine-pyrimidine transport system of H. diminuta contains at least three distinct transport loci and that two of these loci contain multiple substrate binding sites. The three loci are characterized as follows: (1) A thymine-uracil locus which is responsible for the absorption of thymine and uracil via allosteric mechanisms and, therefore, apparently contains two binding sites for these pyrimidines. Adenine and hypoxanthine are non-productively bound to this locus; purine and 6-methyluracil are also bound to this locus, but it is unknown if binding is productive. (2) A locus which transports hypoxanthine (denoted as hypoxanthine locus no. 1), guanine, and adenine. The latter purine is apparently transported by an allosteric mechanism and, therefore, this locus apparently contains two adenine binding sites. Uracil and 5-bromouracil also bind to this locus, however, the nature of binding is uncertain. (3) A second hypoxanthine locus (hypoxanthine locus no. 2) can also be demonstrated which nonproductively binds adenine. Purine is also bound to this locus, but it is unknown if this binding is productive.

Type
Research Article
Information
Parasitology , Volume 66 , Issue 3 , June 1973 , pp. 525 - 538
Copyright
Copyright © Cambridge University Press 1973

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References

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