Table 2. Diagnostic b and y Ions of Phosphorylated IR Peptides^b.

product	phosphorylation site	tR, min	precursor [M + 3H]3+	b4	b5	y3	y4	y5	immonium ion
IR0		5.99	541.6	X	X	X	X	X
IR0 + p	Tyr9	5.89	568.3	X	X	X	X/p	X/p	pY
IR0 + 2p	mostly Tyr9 + Tyr10	5.65	594.9	X	X/p	X/p	p/2p	p/2p	pY
IR0 + 3p	Tyr5 + Tyr9 + Tyr10	5.19	621.6	X	X/p	p	p/2p	p/2p	pY
IR1		5.71	546.6	X	X	X	X	X
IR1 + p	Tyr9	5.60	573.6	X	X	X	X/p	X/p	pY
IR1 + 2p	mostly Tyr9 + Tyr10	5.30	600.2	X	X	p	p/2p	p/2p	pY and pl-DOPA
IR1 + 3p	Tyr5 + Tyr9 + Tyr10	5.17	626.9	X	X/p	p	2p	2p	pY and pl-DOPA
IR2		5.50	552.3	X	X	X	X	X
IR2 + p	Tyr9	5.37	578.9	X	X	X	X/p	X/p	pY
IR2 + 2p	mostly Tyr9 + Tyr10	5.30	605.6	X	X	X/p	p/2p	2p	pY and pl-DOPA
IR2 + 3p	Tyr5 + Tyr9 + Tyr10	5.15	632.2	X	p	a	2p	2p
IR3		5.24	557.6	X	X	X	X	X
IR3 + p	Tyr9	5.30	584.2	X	X	X	X/p	X/p	pl-DOPA
IR3 + 2p	mostly Tyr9 + Tyr10	5.27	610.9	X	X/p	X/p	p/2p	X/p/2p	pl-DOPA
IR3 + 3p	Tyr5 + Tyr9 + Tyr10	5.13	637.6	X	p	p	p/2p	p/2p	pl-DOPA

^aNot observed.

^bNonphosphorylated fragments are marked with X, singly phosphorylated fragments with p, and doubly phosphorylated fragments with 2p. Present phosphotyrosine immonium ion is marked as pY and phospho-l-DOPA immonium ion as pl-DOPA. Accurate masses, relative abundances, and mass accuracies are provided in Table S5.