Nitrobenzylthioinosine binding cooperativity in chromaffin tissue membranes.
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.
Casillas
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Departamento de Bioquímica, Facultad de Veterinaria, Universidad Complutense de Madrid, Spain.
Sen
R P
RP
Delicado
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EG
Miras-Portugal
M T
MT
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
D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D013868:Thioinosine; D000255:Adenosine Triphosphate; C001789:4-nitrobenzylthioinosine