TABLE 2.

Anomalous exponent, diffusion rate, and exclusions per unit time for raft-excluded proteins in a membrane

		Diffusion rate		Anomalous exponent		Exclusion rate
Total raft area	Raft diameter (nm)	Mobile	Fixed	Mobile	Fixed	Mobile	Fixed
10%	14	0.722	0.623	0.866	0.853	85.8	72.4
25%	14	0.786	0.842	0.813	0.652	214.0	200.6
50%	14	0.825	0.544	0.745	0.634	377.9	506.0
10%	50	0.556	0.472	0.993	1.017	66.7	64.46
25%	50	0.489	0.5	1.045	0.976	64.0	59.36
50%	50	0.602	0.486	1.024	0.99	64.2	55.7

The first column shows the proportion of the membrane that is raft associated. If rafts are mobile, the diffusion rate is obtained from the Saffman-Delbruck equation (24,33). The expected diffusion rate (units of voxels²/time unit) if no objects are present on the membrane is 0.5. The last column shows the number of exclusion events per unit time in each case, which is approximately inversely proportional to the anomalous exponent, as would be expected. Note that the diffusion rate can exceed 0.5 in some cases. This is caused by proteins moving along “raft-free channels”, in which case their motion is no longer accurately described by the diffusion equation. The anomalous exponent in some cases slightly exceeds 1 for the same reason. The effect of this phenomenon on the reliability of α-values obtained in these cases is insignificant, since the difference from the expected value of D is very small and the log(MSD) − log(time) plots are all linear.