FIGURE 5.

A chimeric MS² spectrum revealing a pair of isomeric differently modified α1(V) chain peptides that co-eluted and co-fragmented. Peptides were generated by AspN cleavage of bovine placenta α1(V) chains. MS¹ in the insert was obtained by averaging MS¹ across the elution window. MS² revealed that the two separate cluster peaks in MS¹ belong to peptides with identical primary sequence but to differing degrees of hydroxylation. Peptides with a total of three hydroxylations contain Hyp⁶⁹³, Hyp⁶⁹⁶, and Hyp⁷⁰⁵ (MS² for peptides with a total of 3 hydroxylation in the MS¹ of the inset is not shown here). MS² for peptides with a total of four hydroxylations (shown here) reveals that the extra Hyp can be either Hyp⁶⁹² or Hyp⁶⁹⁵.