TABLE 3.

Membrane penetration depths of the tryptophan residue in single-tryptophan analogs of gramicidin by the parallax method

Gramicidin analog	Depth from the center of the bilayer zcF (Å)
Gramicidin (channel)*	11.0
Gramicidin (nonchannel)*	7.3
W(11,13,15)BgA	1.3
W(9,13,15)BgA	5.5
W(9,11,15)BgA	10.7
W(9,11,13)BgA	12.5

Depths were calculated from fluorescence quenchings obtained with samples containing 15 mol % of 5-PC and 12-PC and using Eq. 1. Samples were excited at 280 nm, and emission was monitored at 335 nm. The gramicidin/total lipid ratio was 1:50 (mol/mol). See Materials and Methods for other details.

^*From Rawat et al. (28).