Figure 3.

Fluorescence emission intensity vs. 6-IATR-labeled myosin concentration on the motility surface. (A) Only the y-polarized fluorescence from a mixture of labeled and unlabeled myosin on the motility surface is shown at 1-ms integration rate for mixtures containing 0, 0.5, 1.0, and 10 μg/ml of labeled myosin. The peak fluorescence of 248 counts at 10 μg/ml labeled myosin is not shown so that the ordinate could be the same for all traces. At 0.5 μg/ml-labeled myosin, quantal photobleaching events are apparent. A more detailed view of unitary photobleaching events for both the x- (○) and y-polarized (•) emission at 1.0 μg/ml-labeled myosin in the mixture is shown. (B) The log of peak fluorescence emission intensity vs. the log of labeled myosin concentration in the myosin surface mixture plotted with linear regressions through the data between 0 and 0.25 μg/ml and between 0.13 and 100 μg/ml. Data points are presented as the mean (•) and standard error for at least seven measurements per concentration. The numbers next to the data points are the estimated number of labeled myosin molecules that exist in the excitation spot based on previous myosin surface density estimates (27).