Dear Tim,

thanks a lot. I`m quite limited in the choice of amino acid used for labelling as I want to look at some particular peptides with a modification.

The paper makes a strong case for a limited biosynthesis in presence of an amino acid in the medium and it`s interesting that you also observe that in your lab as well. I might try to do a lysine labelling experiment in parallel with my arginine ones. That should tell if the lower labelling efficincy I observe is due to differences in my method or a lysine vs arginine effect.

Thanks, Michael