title: A kinetic analysis of the uptake of cytosine-beta-D-arabinoside by rat-B77 cells. Differentiation between transport and phosphorylation.
abstract: We present here a differentiation by kinetic methods of the tandem processes of transport and metabolic during uptake of cytosine-beta-D-arabinoside by intact rat fibroblasts. Transport across the cell membrane occurs by a carrier-mediated mechanism displaying a Km of approximately 500 microM and a V of approximately pmol x min-1 x (10(6) cells)-1. The subsequent metabolic trapping (phosphorylation) has a Km of approximately 15 microM and V of approximately 0.25 pmol x min-1 x (10(6) cells)-1. In this system, transport is rate-limiting for the first phase of the uptake process whereas phosphorylation becomes rate-limiting when internal concentration of radioactive labeled substrate exceeds that in the extracellular medium. The duration of the first phase depends on the substrate concentration.
mesh_terms: D000818:Animals; D001358:Avian Sarcoma Viruses; D001693:Biological Transport, Active; D002462:Cell Membrane / Q000378:metabolism; D002472:Cell Transformation, Viral; D003561:Cytarabine / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D010766:Phosphorylation; D051381:Rats; D013997:Time Factors
chemical_list: D003561:Cytarabine