FIGURE 8.

Determination of the E_act of denaturation for native and cross-linked rhodopsin in disk membranes. Representative thermograms and plots of ln() versus 1/T_m for (A and D) unbleached native disk membranes, (B and E) 16% dimeric rhodopsin in cross-linked disk membranes, and (C and F) 34% dimeric rhodopsin in cross-linked disk membranes. The thermograms were acquired at scan rates of 1.5°/min (solid curves), 1.0°/min (dashed curves), 0.5°/min (dotted curves), and 0.25°/min (dashed-dot-dashed curves). The scan rates and T_ms of each endothermic (solid circles) and exothermic (open circles, for the cross-linked samples only) transition were used for the modified Arrhenius plots. At least two T_m values for each transition were used. The E_acts for the transitions were determined from the slope of each ln() versus 1/T_m plot according to the equation ln() = const. − E_act/R(1/T_m) (20,24) (see Materials and Methods). Lines are best fit as determined by linear regression.