Summary of 3Hyp occupancy in the (GPP)_n of type I and II collagen α-chains.

<p>The table shows the average number of 3Hyp residues per (GPP)_n motif with the percentage of α-chains containing at least one 3Hyp residue per (GPP)_n given in parentheses. The percentage of each posttranslational variant was determined based on the ratio of the heights of the m/z peaks. For example, the human tendon α1(I) (GPP)_n tryptic peptide, TGDAGPV<b>GPPGPPGPPGPPGPP</b>SAGFDFSFLPQPPQE<b>K</b>, was found to be a mix of eight distinct molecular species giving a hydroxylation (±16 Da) ladder, each representing a posttranslational variant (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093467#pone-0093467-g002" target="_blank">Figure 2</a>). The molecular location of the each hydroxylated residue (3Hyp, 4Hyp and Hyl) was determined using MS/MS (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093467#pone.0093467.s001" target="_blank">Figure S1</a>). The C-terminal lysine was predominantly hydroxylated in all Achilles tendons. In this scroll, the 1270.7³⁺ m/z (peptide species containing four 3Hyp residues and five 4Hyp) represents 9% of the total population and the other variations are as follows: 1265.9³⁺ (three 3Hyp residues and five 4Hyp, 10%); 1260.5³⁺ (three 3Hyp residues and four 4Hyp, 13%); 1254.6³⁺ (two 3Hyp residue and four 4Hyp, 19%); 1249.6³⁺ (one 3Hyp residue and four 4Hyp, 16%); 1244.1³⁺ (no 3Hyp residues and four 4Hyp, 18%); 1238.6³⁺ (no 3Hyp residues and three 4Hyp residue, 10%); 1233.1³⁺ (no 3Hyp residues and two 4Hyp residue, 5%). From these percentages, the average number of 3Hyp residues was estimated per α-chain. In this example the calculation is (4×9%)+(3×10%)+(3×13%)+(2×19%)+(1×16%) = mean content of 1.6 3Hyp per α1(I) from human tendon. The 3Hyp content in mouse tendon type I collagen was observed to vary markedly with animal age, in the range between one and two 3Hyp residues per (GPP)_n as indicated in the table.