Table I. Circulating human Oc fragments observed by MSIA in 130 samples from studies A–C.

Truncated Peptide (Descending MW)	Designation in Fig. 1	aMALDI Obs. MH+Avg	Calc. MH+Avg	aESI Obs. MH+Mono	Calc. MH+Mono	bFractional Abundance (S.D.)
Y[1–49]V	A	5798.4	5798.5	5794.65	5794.75	48.9 (9.9)
Y[1–48]P	B	5699.7	5699.3	5695.48	5695.68	4.6 (1.1)
L[2–49]V	C	5635.4	5635.3	5631.50	5631.68	3.6 (0.9)
Y[3–49]V	D	5522.5	5522.1	5518.46	5518.60	17.1 (4.2)
Y[3–48]P	E	5423.8	5423	5419.46	5419.53	4.7 (1.5)
cpE[4–49]V	F	5342.4	5342	5338.53	5338.52	11.4 (3.9)
pE[4–48]P	G	5242.3	5242.8	5239.35	5239.47	1.1 (0.5)
d W[5–49]V	H	5230.6	5230.8	5227.48	5227.48	1.6 (0.7)
W[5–48]P	I	5131.4	5131.7	5128.36	5128.41	1.7 (0.8)
G[7–49]V	J	4930.6	4931.5	eN.O.	4928.31	1.2 (1.0)
Y[1–42]Y	K	4921.4	4922.4	N.O.	4919.27	0.3 (0.5)
fA[8–49]V	L	4873.5	4874.4	N.O.	4871.29	2.3 (2.4)
Y[1–41]A or L[2–42]Y	M	4758.1	4759.3	N.O.	4756.21	1.5 (1.3)

^a For MALDI spectra MH⁺ designates the intact, protonated gas phase ion analyzed by the mass spectrometer. For ESI spectra it represents the charge state-deconvoluted mass of the protonated molecule. Since protein isotopes are not resolved by MALDI-MS, MH⁺_Avg refers to the average molecular mass (in Da). Since protein isotopes are resolved by ESI-MS, MH⁺_mono refers to the monoisotopic molecular mass (in Da). Observed mass values were taken from representative individual spectra. Multiple γ-carboxylated forms of each species were also observed by ESI.

^b Fractional abundance as determined by MALDI-MSIA (which includes, but does not discriminate between all Gla-containing proteoforms); expressed as average percentage ± S.D. for all samples in Supplemental Fig. 5b (n = 130).

^c pE = Pyroglutamic acid, formed spontaneously when Q was at the N-terminus.

^d Previously observed as a product of MMP -1, -2, and -8 digestion of human Oc (41).

^e N.O. indicates fragment not observed.

^f Previously observed in bovine serum (42) and as a product of cathepsin digest (43).