Figure 7.

Kinetics of Cl− transport by CLC-ec1 Cl−-dump experiments as in Fig 6 were analyzed in two different ways. (A) Initial-velocity method. Initial rate of Cl− efflux was determined as a function of protein density p in the reconstitution mix. These experiments employed protein densities <0.5 μg/mg, where the plot is linear and initial rates can be measured accurately. Each point represents a single time course. The regression line represents a unitary turnover rate of 4,060 s−1. (B) Poisson method. The "average time constant" 〈τ〉 for CLC-mediated Cl− transport was measured by fitting Cl− efflux traces at the indicated protein densities. Each point represents three to four measurements. Solid curve is fit to the data according to Eq. 7, using nine terms in the infinite sum. The fit value of the 〈τ〉 intercept τ* is 54.3 s, and of p0, which gives the initial slope of the curve, is 0.19 μg/mg.