Table 1.

Percent oxidations after cold chemical oxidation of apomyoglobin. The %'s were calculated from the ratio of the signal for the modified peptide divided by that for the unmodified peptide; the apomyoglobin was incubated for 2 h with 100 mM H₂O₂ at −80 or −15 °C. The water exposure and % oxidized were calculated as described in the experimental section.

Residue Type	% Ox (−80 °C)	%Ox (−15 °C)	Protein Water Exposure (Å2)
Trp-7	3%	2%	19
Trp-14	Ya	Ya	7
Tyr-103	0.2%	0.2%	28
Tyr-146	6%	6%	18
Met-55	Y	Y	16
Met-131	56%	82%	0
Phe-33	ndb	ndb	6
Phe-106	0.01%	0.01%	36
Phe-123	Y	Y	9
Phe-138	2%	2%	30
Phe-151	Y	Y	38
His-24	1%	0.8%	12
His-36	0.9%	0.8%	29
His-64	Y	Y	28
His-81	xc	xc	64
His-82	x	x	9
His-93	x	x	37
His-97	x	x	38
His-113	Y	Y	48
His-116	0.03%	0.1%	47
His-119	0.2%	0.7%	24
Val-10	nd	nd	0
Val-13	nd	nd	8
Val-17	0.5%	0.2%	0
Val-28	nd	nd	0
Val-67	nd	nd	112
Val-68	0.2%	0.3%	44
Val-114	nd	nd	10

^aY annotation indicates that the oxidized peptide was detected but could not be quantified owing to interference and/or poor chromatographic resolution.

^bThe nd annotation indicates that the modified peptide was not detectable although the unmodified peptide was. The detection limits were in all cases better than 1% and for 80% of the detections, the detection limits were 0.2% or better. Detection limits are variable owing to differences in the ionization efficiencies of the tryptic peptides.

^cThe x annotation indicates that the unmodified peptide carrying the denoted residue was not observed (was not retained on the reverse phase column); therefore, no conclusion regarding the reactive residue can be drawn.