Premium
Purine Nucleoside and Nucleobase Cell Membrane Transport in Giardia lamblia
Author(s) -
BAUM KENNETH F.,
BERENS RANDOLPH L.,
MARR J. JOSEPH
Publication year - 1993
Publication title -
journal of eukaryotic microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 1066-5234
DOI - 10.1111/j.1550-7408.1993.tb06122.x
Subject(s) - nucleobase , nucleoside , nucleoside transporter , purine , biology , biochemistry , nucleoside analogue , membrane transport , substrate (aquarium) , stereochemistry , chemistry , transporter , enzyme , dna , membrane , ecology , gene
.Giardia lamblia is dependent on the salvage of preformed purines and pyrimidines. This study investigated purine nucleoside and nucleobase transport utilizing rapid uptake determinations. Nucleoside substrate/velocity curves exhibited the hyperbolic kinetics of a saturable carrier‐mediated system. Deoxynucleosides exhibited a much lower affinity for the transporter. Inhibition studies confirmed the relative camer affinities of these ribonucleosides and deoxyribonucleosides. The nucleobase adenine did not exhibit saturation lunetics at a comparable substrate range, and did not inhibit nucleoside transport. Dipyridamole markedly inhibited nucleoside but not nucleobase transport, confirming the separate entry pathways. When cells were depleted of ATP, the velocity of nucleoside and nucleobase transport was unchanged, indicating that it is a non‐energy‐dependent process. Three nucleoside analogs, formycin A, adenine arabinoside and 7–deazaadenosine, were studied. Transport kinetics ranged widely among this group and could not completely account for their cytotoxic effect. When the apparent Km and Vmax of the nucleosides were compared, an approximately linear relationship (r 2 = 0.95) was noted. This suggests that a high affinity of the nucleoside permease for the substrate retards disassociation of the substrate‐carrier complex, slowing net influx.