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

The presence of [H-3] 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 (k(1) and k(-1)) were 3.95 +/- 0.57 x 10(8) pH min(-1) and 0.025 +/- 0.002 min(-1), respectively. The number of binding sites was 2,100 +/- 163 fmols/mg protein. [H-3] NBMPR binding was inhibited, in a nanomolar range, by NBMPR (K-I = 0.23 +/- 0.02 nM), OH-NBMPR (K-I = 2.30 +/- 0.55 nM) and HNBTG (K-I = 2.58 +/- 0.33 nM) In the micromolar range, adenosine receptor ligands such as PIA (3.46 +/- 1.36 mu M), 2-chloroadenosine (18.81 +/- 3.36 mu M) and NECA (8.26 +/- 3.90 mu M), and mitochondrial benzodiazepine receptor ligands such as Po 5-4864 (5.15 +/- 1.82 mu M) and PK 11195 inhibited the specific binding of [H-3] NBMPR. These results suggest the existence of a nucleoside transport system in the mitochondrial fraction of rat testis.