Parameter compensations affecting binding parameter identifiability for three-site binding curves. (A and B, top) Fit-error curves for shape parameter a (A) and shape parameter b (B) for three-site binding curve (curve A in Fig. 10) for which (a, b) = (10, 0.1). Dashed horizontal lines indicate 5% rms error level. (A, middle) Examples of fits to synthetic data curve from selected points labeled A–G on curve in A (top). Fits were obtained using nonlinear regression while holding shape parameter a fixed to the value indicated by the corresponding letter in A (top) and varying parameters p1 and b to achieve best fit. (B, middle) Same as A (middle), except fits are from selected points on curve in B (top), and fits were performed holding shape parameter b fixed while p1 and a were varied to achieve best fit. (A and B, bottom) Trajectories of parameters a, b, and p1 for all fits used to construct fit-error curves in A and B (top). (C and D, top) Fit-error curves for shape parameter a (C) and shape parameter b (D) for three-site binding curve (curve B in Fig. 10) for which (a, b) = (10−4, 10−4). (C, middle and bottom) Same as for A (middle and bottom), except fits and parameter trajectories were from points in C (top). (D, middle and bottom) Same as for B (middle and bottom) B3, except fits and parameter trajectories were from points in D (top). Spacing parameter Δ2 is illustrated for binding curve in A (middle). Synthetic data curves in A–D (middle) are indicated by red dots.
