TABLE 1.

Theoretical and observed masses of the parent ion containing the phenylhydrazine-derivatized LTQ cross-link

Mass (theoretical)	Mass (observed)	Parent iona,b,c
1739.2	1738.7	(α+β+PH+3H)3+
1304.7	1304.6	(α+β+PH+4H)4+
1043.9	1044.2	(α+β+PH+5H)5+

^a α = peptides 670–690, containing Tyr-689 of the LTQ cofactor, minus 2H⁺.

^b β = peptides 648–669, containing Lys-653 of the LTQ cofactor, minus H⁺.

^c PH = phenyl–N=N–.