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Purine nucleoside and nucleobase cell membrane transport in Giardia lamblia. 1993

K F Baum, and R L Berens, and J J Marr
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262.

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 carrier affinities of these ribonucleosides and deoxyribonucleosides. The nucleobase adenine did not exhibit saturation kinetics 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 (r2 = 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.

UI MeSH Term Description Entries
D007461 Iodoacetates Iodinated derivatives of acetic acid. Iodoacetates are commonly used as alkylating sulfhydryl reagents and enzyme inhibitors in biochemical research. Iodoacetic Acids,Acids, Iodoacetic
D011687 Purines A series of heterocyclic compounds that are variously substituted in nature and are known also as purine bases. They include ADENINE and GUANINE, constituents of nucleic acids, as well as many alkaloids such as CAFFEINE and THEOPHYLLINE. Uric acid is the metabolic end product of purine metabolism.
D002462 Cell Membrane The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells. Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D000241 Adenosine A nucleoside that is composed of ADENINE and D-RIBOSE. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Adenocard,Adenoscan
D000818 Animals Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA. Animal,Metazoa,Animalia
D001692 Biological Transport The movement of materials (including biochemical substances and drugs) through a biological system at the cellular level. The transport can be across cell membranes and epithelial layers. It also can occur within intracellular compartments and extracellular compartments. Transport, Biological,Biologic Transport,Transport, Biologic
D013868 Thioinosine Sulfhydryl analog of INOSINE that inhibits nucleoside transport across erythrocyte plasma membranes, and has immunosuppressive properties. It has been used similarly to MERCAPTOPURINE in the treatment of leukemia. (From Martindale, The Extra Pharmacopoeia, 30th ed, p503) 6-Mercaptopurine Riboside,NSC-4911,Ribosyl-6-mercaptopurine,6 Mercaptopurine Riboside,Riboside, 6-Mercaptopurine,Ribosyl 6 mercaptopurine
D016829 Giardia lamblia A species of parasitic EUKARYOTES that attaches itself to the intestinal mucosa and feeds on mucous secretions. The organism is roughly pear-shaped and motility is somewhat erratic, with a slow oscillation about the long axis. Giardia duodenalis,Giardia intestinalis,Lamblia intestinalis,Giardia lamblias
D019807 Iodoacetic Acid A derivative of ACETIC ACID that contains one IODINE atom attached to its methyl group. Monosodium Iodoacetate,Monoiodoacetic Acid,Sodium Iodoacetate,Acid, Iodoacetic,Acid, Monoiodoacetic,Iodoacetate, Monosodium,Iodoacetate, Sodium

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