TABLE 2.

Theoretical and observed masses of GC-C ligand peptides

Peptide	Mass (Da)
	Theoretical			Observeda
	Native	Reduced	Reduced and alkylated	Native	Reduced and alkylated
SThb	2,042.3	2,048.3	2,390.5	2,041.6	2,389.8
STpb	1,972.3	1,978.3	2,320.5	1,971.7	2,319.9
Uroguanylin	1,667.9	1,671.9	1,900.0	1,667.7	1,899.8
Guanylin	1,458.7	1,462.7	1,690.8	1,458.6	1,690.6

^aObserved monoisotopic peaks in mass spectrometry. All peptides bound Na⁺ and/or K⁺ to some degree. The reported masses are without binding of ions.

^bSynthetic STh and STp peptides had the same observed masses as those of peptides purified from ETEC.