Table 1.

Mass spectroscopic identification of pY53-actin

	Mass, Da
	Observed	Calculated
N-acetyl-actin	41,658.37	41,657.68
N-acetyl-actin plus phosphatase	41,657.47	41,657.68
N-acetyl-pY53-actin	41,737.84	41,737.66
N-acetyl-pY53-actin plus phosphatase	41,657.35	41,657.68
Peptide A	1,197.52	1,197.52*
Peptide B	1,277.49	1,277.48

*Assumes peptide A is residues 51–61, DSYVGDEAQSK, and peptide B is peptide A phosphorylated on Y53. The peptide masses are monoisotopic.