Table 1. Identification of IgG and Fc fusion protein domains by RP LC-MS.

IgG subclass	Molecule	Domain	Theoretical mass (Da)*	Observed mass (Da)
IgG1	A1	Fc/2 Fd LC	25236 25384 23443	25236 25385 23444
	A2	Fc/2 Fd LC	25236 25754 23278	25236 25754 23278
	A3	Fc/2 Fd LC	25204 25648 23439	25203 25648 23438
	A4	Fc/2 Fd LC	25236 25469 23429	25235 25468 23428
	A5	Fc/2 Fd LC	25204 25459 23412	25203 25459 23412
IgG2	B1	Fc/2 Fd LC	25238 25104 23416	25238 25103 23416
	B2	Fc/2 Fd LC	25238 24964 23439	25238 24966 23439
	B3	Fc/2 Fd LC	25270 25223 22948	25270 25224 22948
IgG4	C1	Fc/2 Fd LC	25220 25514 23745	25219 25514 23744
	C2	Fc/2 Fd LC	25220 25503 23745	25219 25504 23744
Fc fusion	F1	Fc/2	25236	25236

*Mass of fully reduced domains based on cleavage sites shown in Figure 3, G0F glycoform and fully processed C-terminal lysine for Fc/2, and complete conversion of N-terminal Q1 to pE1 for Fd and LC.