Kate Koles raised a question of lack of [3H]-L-fucose labeling in double labeling with [14C]leucine. I think the reason may be due to the difference of incor-poration rate between leucine and fucose. The pulse time of 50 min should be
sufficient for leucine to incorporate into protein backbones, whereas fucose
presence takes longer time (it normally occurs on complex typed oligosaccharidesduring the post-translational modification). In my experience, I had to "pulse"for an extended 12 hrs before harvesting. So, prolong the labeling time to see
if it would help the labeling efficiency.
Ke-Wei Zhao, Ph.D.
Dept. of Biol. CHem.
UCLA School of Medicine