Figure 3.

Time course of dATP/ADP exchange and substrate specificity of human DNC. (a) Time course of [α-³⁵S]dATP/ADP exchange in proteoliposomes reconstituted with the recombinant DNC. [α-³⁵S]dATP (1 mM) was added to proteoliposomes containing 10 mM ADP (⋄) or 10 mM NaCl (▿) (b) Dependence of DNC activity on internal substrate. Proteoliposomes were preloaded internally with various substrates (concentration 10 mM). Transport was started by addition of 20 μM [α-³⁵S]dATP and stopped after 2 min. The values are means ± SD of at least three experiments. (c) Inhibition of the rate of [α-³⁵S]dATP uptake by external substrates. Proteoliposomes were preloaded internally with 10 mM ADP. Transport was started by adding 125 μM [α-³⁵S]dATP and stopped after 2 min. External substrates (concentration 0.5 mM) were added together with [α-³⁵S]dATP. The extents of inhibition (%) from a representative experiment are reported. The control value for uninhibited exchange was 0.45 mmol/min per gram of protein.