Fig. 3.
Processivity and ATP dependence of transport. (A) The amplitude of the transport signal for tandem pSpy4× series with 50 µM pSpy2× (pink) or 10 µM SecAD209N (cyan) added at the same time as the ATP. The equivalent data with only ATP, performed in parallel, are shown in dark pink and blue, respectively (n.b., these overlay very closely, largely obscuring the blue data). The fits are to exponential decay and normalized to the fitted value of A0 with only ATP. (B) Lag as a function of active Pep86 position in the Spy4× series, at a range of ATP concentrations: red = 320 µM, orange = 160 µM, yellow = 80 µM, green = 40 µM, teal = 20 µM, blue = 10 µM, and purple = 5 µM. The fits are to straight lines. (C) The transport rate (black circles) and x intercept (orange squares) extracted from the fits in B as a function of ATP concentration. The transport is fitted to the Michaelis–Menten equation (black line), while the orange line is the mean x intercept. (D) A as a function of [ATP] for the Spy4× series. The lines are global fits to a weak binding equation.