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Characterization of nitrobenzylthioinosine binding sites in the mitochondrial fraction of rat testis

Abstract:

The presence of [3H] NBMPR binding sites in the mitochondrial fraction of rat testis is described. The dissociation constant (K(D)) from saturation studies was 0.16 ± 0.04 nM. The association and dissociation rate constants (k1 and k-1) were 3.95 ± 0.57 x 108 M-1 min-1 and 0.025 ± 0.002 min-1, respectively. The number of binding sites was 2,100 ± 163 fmols/mg protein. [3H] NBMPR binding was inhibited, in a nanomolar range, by NBMPR (K1 = 0.23 ± 0.02 nM), OH-NBMPR (K1 = 2.30 ± 0.55 nM) and HNBTG (K1 = 2.58 ± 0.33 nM). In the micromolar range, adenosine receptor ligands such as PIA (3.46 ± 1.36 μM), 2-chloroadenosine (18.81 ± 3.36 μM) and NECA (8.26 ± 3.90 μM), and mitochondrial benzodiazepine receptor ligands such as Ro 5-4864 (5.15 ± 1.82 μM) and PK 11195 inhibited the specific binding of [3H] NBMPR. These results suggest the existence of a nucleoside transport system in the mitochondrial fraction of rat testis.