Table 1.

Masses of Cys-containing peptides for alkylated, de-N-glycosylated, tryptic digests of NL3-639 proteins ^a

			Observed masses
Disulfide linkages	NL3-639 peptides	Calculated massesb	Wild type	R471C
C106-C141	D98-R195c	6628.56d	6627.69	6628.11
C293e	I282-R309	2974.42	2974.43	2974.40
C340-C351	V338-R353	1749.81	1749.78	1749.76
C510-C544	Y497-K548c	5877.69	5877.85	5876.64f

^a Seventy-three percent of NL3-639 amino acid sequence was accounted for in acquired mass spectra. The small tryptic peptide (471-K472 of the R471C mutant is not observed being below the limit of mass detection.

^b Masses are calculated from amino acid sequence (monoisotopic masses are given below 2000 Da, average masses above 2000 Da).

^c Native Asn is converted to Asp by PNGase F treatment.

^d Numbering includes an alternative splice sequence of 40 aa not found in NL3.

^e Free Cys293 is alkylated by iodoacetamide treatment of NL3 proteins.

^f Weak ionization signal compared with wild type.