A, typical frequency changes of the DNA-immobilized QCM, in response to the addition of EcoRII. Curve a, 2-site DNA with Mg2+ ions; curve b, 2-site DNA with Ca2+ ions; and curve c, 1-site DNA with Mg2+ ions. ([EcoRII] = 5 nm, [DNA] = 19 ± 1 ng (0.55 ± 0.02 pmol) cm–2 on a QCM, [MgCl2 or CaCl2] = 5 mm, 10 mm Tris-HCl, pH 7.5, 50 mm NaCl, 1 mm DTT, 25 °C). B, curve a, calculated time dependence of the [β-ES] complex as shown in Equation 7 in the text; curve b, calculated time dependence of the [α-ES] as shown in Equations 8 and 9 in the text; curve c, fitted curve obtained from the simultaneous Equations 7, 8, 9; and curve d, experimental curve at [EcoRII] = 5 nm and [2-site DNA] = 19 ng (0.55 pmol) cm–2 on a QCM. C, linear reciprocal plots of the relaxation rate (τ–1) obtained from Equation 7 against the EcoRII concentration. The kon and koff values can be obtained from the slope and the intercept, respectively, according to Equation 5 in the text.