Figure 7.

The relationship between the rate and extent of trapping suggests that the S729C mutant disulfide bond has a limited lifetime. A, Bar plot summarizing the rate of trapping for the S729C and L483Y-S729C mutants in different conditions. Trapping is fastest in the presence of 50 μm glutamate. The L483Y mutant slows trapping, and in the presence of CNQX trapping was eliminated; the bar for LY-SC CNQX is an upper estimate of the trapping rate given that we observed no trapping after 360 s. B, Bar plot summarizing the extent of trapping in the steady state for the same conditions as in A. C, The proportion of receptors that were not trapped in steady-state conditions showed a strong negative correlation to the trapping rate. These data were reasonably well described by a simple isotherm where the lifetime of the disulfide trapped conformation was 25 s. The LY-SC CNQX point (open circle) was not included in the fit. Although two disulfide bonds presumably form in a fully trapped tetrameric receptor, we do not know the activity of a singly trapped receptor, and so we did not include this complexity in our fitting.