NS3h_1b(con1) catalyzed DNA unwinding in the presence of an enzyme trap (single turnover conditions). Reactions were performed by rapidly mixing 150 μl from syringe A containing 50 mM MOPS pH 6.5, 10 nM DNA-substrate, 50 nM NS3h, 4 mM MgCl2 with 150 μl from syringe B containing 1 mM NTP and 2 μM of the oligocucleotide dT20 (5′-TTTTT TTTTT TTTTT TTTT-3′). Final concentrations were 25 mM MOPS pH 6.5, 5 nM DNA substrate, 25 nM NS3h, 2 mM MgCl2, 0.5 mM NTP and 1 μM dT20. (a) Three independent reactions (red, green, blue lines) in which unwinding of a 17 bp DNA substrate was monitored in the presence of ATP, dTTP, and GTP. (b) Three independent reactions (red, green, blue lines) in which unwinding of a 30 bp DNA substrate was monitored in the presence of ATP, dTTP, and GTP. Data were fit to a two-phase rate equation (equation (4)) to yield the rate constants and amplitudes summarized in Table 1. Curve fits are shown as solid black lines.