Observed Mass	N-terminus	Possible Product
M – 1	Any	Keto-protein
M + Alk – 19	Any	Oxime
M – 44	Asp	Decarboxylation (still can form oxime)
M – 16	Ser	Beta elimination (still can form oxime)
M – 32	Cys	Beta elimination (still can form oxime)
M + 247	Any	PLP aldol addition
M + 229	Any	PLP aldol addition with dehydration
M + 229	His, Trp	Pictet-Spengler addition of PLP
M – 19	Lys	Cyclic enamine
M + 293	Pro	Ring opening with PLP addition