Table 2. Analyses by MALDI-TOF MS of H. pylori ThyX mutant proteins.

Protein substitution	Predicted mass, Da	Observed mass, Da*
None (wild-type)	27,169.9	27,168.2
H48Q	27,159.9	27,155.7
S84A	27,152.9	27,146.9
S84C	27,185.0	27,493.1
Peptide (S84C)	2,375.308†	2,695.320
LSRHRIASLSVKCSRYTLRE

^*The precision of MALDI-TOF measurements was 0.05% for proteins and 0.008% for peptides.

^†The value shown is for a nonderivatized cysteine residue. Expected value for carbamidomethylated C84 would be 2,432.330.