3
Figure 6-4. Plot of the initial rate of increase of specifically-bound [ H]dexamethasone
(normalized by the receptor concentration B ) as a function of the total ligand
concentration S. for the six experimental determinations of the l H]dexamethasone
association rate constant (k ).
a
The ordinates were determined in two different ways: first, the slope of the line fit by linear
regression to the first three points of the temporal binding curve (e.g., inset to figure 6-1) was
taken as the estimate of dBSp/dt(initial) to generate one set of points ( ); the other set of
points ( ) was generated by calculating the initial slope dB /dt (i.e., equation 6-1: dB /dt=
s p s p
k S,B at t = 0) from the value of k derived from the individual experiment as described in Methods
(e.g., figure 6-1). A line was fit to each set of points by linear regression through a fixed point
(the origin). Although there is considerable scatter in the data, each set of points is at least
consistent with a straight line passing through the origin, indicating that the individual
experiments generated independent measurements of kfl that were not correlated with the ligand
concentrations (S.); furthermore, the two lines were not different. The slope of the line gives
L 5-1-1
an averaged or merged estimate for k : k = 7.02 x 10 M min (from the ^points). Thus, the data
a a
do not support the existence of unobserved transient intermediate states or suggest that incubation
3
times were too long in the experiments performed at the higher [ Hjdexamethasone concentrations.