Figure 4. LTQ quantitation of tandem mass spectra of Aß from human in vivo labeling with two amino acids.
(a) Tandem MS spectra of Aβ17-28 from human CSF thirteen hours after in vivo13C6-leucine labeling demonstrate unlabeled Aβ17-28 tandem MS ions (top) and labeled Aβ17-28 tandem MS ions (bottom). The leucine containing tandem MS ions demonstrate the additional six Dalton label, as shown by arrows to leucine containing ions.
(b) Tandem MS spectra of Aβ17-28 from human CSF twelve hours after in vivo labeling with 13C6-phenylalanine demonstrate unlabeled ions (top), singly labeled ions (middle) and doubly labeled ions (bottom), as shown by arrows to phenylalanine containing ions.