title: Nitrobenzylthioinosine binding cooperativity in chromaffin tissue membranes.
abstract: The nucleoside transporter present in chromaffin tissue membranes has been studied by [3H]nitrobenzylthioinosine (NBTI) binding. This ligand presents a high affinity, with a Kd value of 2.1 +/- 0.2 nM and a Bmax of 1.7 +/- 0.2 pmol/mg protein. From the Scatchard and the semilogarithmic graphical representations a positive cooperativity was deduced, with a Hill coefficient of 1.7 +/- 0.4. In displacement studies of NBTI by the non labelled compound, the Hill coefficient was also higher than 1 (1.44 +/- 0.11) in the presence of ATP. This nucleotide seems necessary to maintain the number of high affinity binding sites.
authors.affiliation: Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
authors.forename: T
authors.initials: T
authors.lastname: Casillas
authors.forename: R P
authors.initials: RP
authors.lastname: Sen
authors.forename: E G
authors.initials: EG
authors.lastname: Delicado
authors.forename: M T
authors.initials: MT
authors.lastname: Miras-Portugal
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D007700:Kinetics; D008565:Membrane Proteins / Q000037:antagonists & inhibitors*; D033703:Nucleoside Transport Proteins; D011485:Protein Binding; D013868:Thioinosine / Q000031:analogs & derivatives* / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D013868:Thioinosine; D000255:Adenosine Triphosphate; C001789:4-nitrobenzylthioinosine